[Haskell-cafe] Re: Haddock: Failed to create dependency graph (when adding sections with * or a module heading)
Simple fix (terrible error message): Move the ( up to the line with the module name. Previous bad code: module Data.DualMap -- * The @DualMap@ abstract type ( DualMap () -- * (?) internal? -- exposed for testing purposes, for now... , dmFlip -- * converting to and from DualMap , toList, fromList, map -- * constructing a DualMap , empty, null, insert, union Happy code looks like this: module Data.DualMap ( -- * The @DualMap@ abstract type DualMap () -- * (?) internal? -- exposed for testing purposes, for now... , dmFlip -- * converting to and from DualMap , toList, fromList, map -- * constructing a DualMap , empty, null, insert, union Simple enough. I found this out by downloading DList [1] from hacakge and gutting it and replacing the code with my own code. When DList worked with 'cabal haddock' and mine didn't (when I tried to add some asterisks), I looked at the difference between the files and sure enough my parenthesis was on the wrong line. BTW I highly recommend DList as a starting place for a new Haskell project instead of hnop [2]. Jared. [1] http://hackage.haskell.org/package/dlist-0.5 [2] http://semantic.org/hnop/ On Wed, Aug 19, 2009 at 9:45 AM, Jared Updike jupd...@gmail.com wrote: I compiled and installed haddock-2.4.2 from the tarball source. Adding a few simple comments to the code here: https://dl.getdropbox.com/u/143480/doc/DualMap.hs and running haddock $ haddock -h -o doc Data/DualMap.hs Warning: Data.DualMap: could not find link destinations for: Data.Typeable.Typeable2 GHC.Base.Eq GHC.Show.Show GHC.Base.Ord GHC.Base.Bool Data.Set.Set yields: https://dl.getdropbox.com/u/143480/doc/Data-DualMap.html Things look good. (Note that this module only depends on libs that ship with GHC and no other source modules.) However, when I try to add sections (a la http://www.haskell.org/haddock/doc/html/ch03s04.html#id289234 ) in the comments with -- * test I get: $ haddock -h -o doc Data/DualMap.hs Data/DualMap.hs:20:0: parse error on input `-- * test' haddock: Failed to create dependency graph I have no idea where to begin getting this to work since this error message only tells me that Haddock.Interface.depanal returned Nothing (according to a grep of the haddock sources) but not how to stop the dependency analysis from failing. Perhaps I need some more command line arguments or references to missing link destinations in GHC/base/containers documentation or some haddock config file? Searching Google yielded plenty of cabal build errors of the same ilk for packages on hackage but nothing about how to fix them. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haddock: Failed to create dependency graph (when adding sections with * or a module heading)
I compiled and installed haddock-2.4.2 from the tarball source. Adding a few simple comments to the code here: https://dl.getdropbox.com/u/143480/doc/DualMap.hs and running haddock $ haddock -h -o doc Data/DualMap.hs Warning: Data.DualMap: could not find link destinations for: Data.Typeable.Typeable2 GHC.Base.Eq GHC.Show.Show GHC.Base.Ord GHC.Base.Bool Data.Set.Set yields: https://dl.getdropbox.com/u/143480/doc/Data-DualMap.html Things look good. (Note that this module only depends on libs that ship with GHC and no other source modules.) However, when I try to add sections (a la http://www.haskell.org/haddock/doc/html/ch03s04.html#id289234 ) in the comments with -- * test I get: $ haddock -h -o doc Data/DualMap.hs Data/DualMap.hs:20:0: parse error on input `-- * test' haddock: Failed to create dependency graph I have no idea where to begin getting this to work since this error message only tells me that Haddock.Interface.depanal returned Nothing (according to a grep of the haddock sources) but not how to stop the dependency analysis from failing. Perhaps I need some more command line arguments or references to missing link destinations in GHC/base/containers documentation or some haddock config file? Searching Google yielded plenty of cabal build errors of the same ilk for packages on hackage but nothing about how to fix them. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell Logo Voting has started!
Wow, I had a nice list of all the numbers of my favorites ranked before voting began (like a week ago), and here they are all re-numbered, rendering all that waste of time... even more of a waste of time... Jared. On 3/17/09, Eelco Lempsink ee...@lempsink.nl wrote: Hi there! I updated a couple of logo versions and ungrouped and regrouped the (former) number 31. Other than that, there was nothing standing in the way of the voting to begin imho, so I started up the competition. By now, I suppose everybody should have received their ballot. If you think you should have received it but didn't, please report it, I can resend the invitation. Also, for people not directly subscribed to the haskell-cafe mailing list, you can still send ballot requests until the end of the competition (March 24, 12:00 UTC). Make sure the message contains 'haskell logo voting ballot request' (e.g. in the subject). Depending on the winner of this voting round we can decide whether we need to continue with variations. Jared Updike already offered to donate a bit of time to help create several variations. But for now, good luck with sorting those options! :) -- Regards, Eelco Lempsink ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Logo Preferences
I agree that we should use the first round of voting to learn what the general consensus of the Haskell community is on a logo design idea (and to filter out the non-viable logos). In the spirit of bikeshedding, I would love to see---and would volunteer to spend part of a day editing, say, the top one or two logos, in Photoshop---generating numerous variations on fonts, colors (text, emblem and background), and relative font/emblem sizes. (Alternately, the original author of the favorite logo(s) could produce said variations.) Then I think we should vote on the final minor variations. I can *almost* picture a few of the current logos becoming the Final logo, but not As Is; there are many great ideas but some of them (or combinations of a few of them) could be improved in minor ways, bringing things (at least to me) up to professional level for a logo. (cf. the python.org logo) Jared. On 3/9/09, Ian Lynagh ig...@earth.li wrote: On Mon, Mar 09, 2009 at 11:13:40AM +, Sebastian Sylvan wrote: Another reason condorcet voting is nice is that there is no need to group similar items together. I think the plan is that once a logo class is chosen, we'll have another vote for the actual colour scheme etc to be used, if applicable. Yes, we could have done this in a single vote, but then people would need to spend time creating 30 variants of each logo, and we'd be ranking 3000, rather than 100, options. Thanks Ian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Data.Map: Enumerating ordered subset of keys
I had a similar thought. That will probably do the trick. Jared. On 2/8/09, Svein Ove Aas svein@aas.no wrote: On Mon, Feb 9, 2009 at 8:02 AM, Jared Updike jupd...@gmail.com wrote: It looks like two Map.splits will do what I need except for allowing more exact testing of = vs. (since == elements are left out of both maps...?) If your key is an instance of Enum, you can use succ/pred to work around that little problem. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Data.Map: Enumerating ordered subset of keys
On 2/8/09, Anish Muttreja anishmuttr...@gmail.com wrote: Maybe you wantData.Map.partition (\key - key = key1 key = key2) map This will return what I want, but partition is O(n) and touches all the keys, so if I had a million keys and only 2 of them matched the key1..key2 range, it would still visit all of them before it enumerated the ones that satisify the predicate. I don't believe laziness would help here. HTH, Anish On Sun, 08 Feb 2009 23:02:37 -0800, Jared Updike jupd...@gmail.com wrote: It looks like two Map.splits will do what I need except for allowing more exact testing of = vs. (since == elements are left out of both maps...?) Jared. On 2/8/09, Jared Updike jupd...@gmail.com wrote: I would like to enumerate a subset of keys in a Map satisfying \ key = key1 key = key2 but in the expected, reasonable amount of time (e.g. O(log(n)) + O(m) for n total keys and m keys in the subset). (Or key key1 and/or key key2 or some such combination). Is there an appropriate idiom or combination of library functions to accomplish this, short of digging into the code for Data.Map and writing such a function for a forked version of Data.Map? For example I could try something like a Set.split of a Set.split of Map.keysSet of my original map, but will laziness magically do what I really want? which is to walk down the tree to key1 (or the nearest key key1) and enumerate keys in order until key2 is reached? Data.Map almost looks like what I need if I can do this. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Map: Enumerating ordered subset of keys
On 2/8/09, Evan Laforge qdun...@gmail.com wrote: I have a little util library with various map functions. 'within' is almost what you want, except it's half-open. You can make an inclusive one by pulling the lowest element off the above map. I'm also curious if there's a better way to do this... -- | Like Map.split, except include a matched key in the above map. split_map :: (Ord k) = k - Map.Map k a - (Map.Map k a, Map.Map k a) split_map k fm = (pre, post') where (pre, at, post) = Map.splitLookup k fm post' = maybe post (\v - Map.insert k v post) at -- | Split the map into the maps below, within, and above the given range. -- @low@ to @high@ is half-open, as usual. split3_map :: (Ord k) = k - k - Map.Map k a - (Map.Map k a, Map.Map k a, Map.Map k a) split3_map low high fm = (below, within, way_above) where (below, above) = split_map low fm (within, way_above) = split_map high above within low high fm = let (_, m, _) = split3_map low high fm in m This looks right to me (correct time complexity). It should do what I need. I will test it and see what I discover. Thanks, Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Data.Map: Enumerating ordered subset of keys
I would like to enumerate a subset of keys in a Map satisfying \ key = key1 key = key2 but in the expected, reasonable amount of time (e.g. O(log(n)) + O(m) for n total keys and m keys in the subset). (Or key key1 and/or key key2 or some such combination). Is there an appropriate idiom or combination of library functions to accomplish this, short of digging into the code for Data.Map and writing such a function for a forked version of Data.Map? For example I could try something like a Set.split of a Set.split of Map.keysSet of my original map, but will laziness magically do what I really want? which is to walk down the tree to key1 (or the nearest key key1) and enumerate keys in order until key2 is reached? Data.Map almost looks like what I need if I can do this. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Data.Map: Enumerating ordered subset of keys
It looks like two Map.splits will do what I need except for allowing more exact testing of = vs. (since == elements are left out of both maps...?) Jared. On 2/8/09, Jared Updike jupd...@gmail.com wrote: I would like to enumerate a subset of keys in a Map satisfying \ key = key1 key = key2 but in the expected, reasonable amount of time (e.g. O(log(n)) + O(m) for n total keys and m keys in the subset). (Or key key1 and/or key key2 or some such combination). Is there an appropriate idiom or combination of library functions to accomplish this, short of digging into the code for Data.Map and writing such a function for a forked version of Data.Map? For example I could try something like a Set.split of a Set.split of Map.keysSet of my original map, but will laziness magically do what I really want? which is to walk down the tree to key1 (or the nearest key key1) and enumerate keys in order until key2 is reached? Data.Map almost looks like what I need if I can do this. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Functional MetaPost in 5 Steps
I'm interested in using Functional MetaPost on Mac OS X (or FreeBSD).
I'm looking for a tutorial like:
http://haskell.org/haskellwiki/Haskell_in_5_steps
but for FMP. I can't even get a simple example to show up in a PDF file:
---
import FMP
... (see full code below)
myPicture = text Hello World
main = do
print $ emit $ metaPost 1 myPicture params
--
When run, this emits MetaPost, which, after running through my shell
script, below, won't show up in my PDF... (this same TeX file will
show an .eps figure I made with PyX, the Python equivalent of FMP,
when I change includegraphics to use that file instead of test.1)
What am I missing? If I can get this working I will gladly write the
FMP 5 Step Tutorial. I like the idea of using FMP but I can't for the
life of me understand why running a toy example is so non-trivial.
(Not to mention undocumented... the manual and tutorials are very
compelling but they don't mention how to get a viewable PDF out of any
of the otherwise enticing examples.)
Jared.
Relevant almost working code:
Test.hs:
---
import FMP
params = Parameters {
prolog = verbatimtex\n\
\\\documentclass{article}\n\
\\\begin{document}\n\
\etex\n\n\
\input boxes\n\
\input FuncMP\n\n,
epilog= \n\n\\end,
defaultDX= 3,
defaultDY= 3,
textDX= 2,
textDY= 2,
newmp= True,
funcmpRTS= IGNORE, --+RTS -H40m -K3M -RTS,
funcmpBin= IGNORE, -- ~/FuncMP-1.2/FuncMP,
mpBin= IGNORE -- MPINPUTS=:~/FuncMP-1.2 TEX=latex mpost
}
myPicture = text blah
main = do
print $ emit $ metaPost 1 myPicture params
--
test.tex:
---
\documentclass[12pt]{article}
\usepackage[dvipdfm]{graphicx}
\begin{document}
\section*{Heading}
\begin{figure}
\begin{center}
\includegraphics{test.1}
\end{center}
\end{figure}
\end{document}
---
shell script:
--
#!/bin/sh
ghc --make Test.hs \
./Test test.mp \
mpost test.mp \
latex test.tex \
latex test.tex \
dvipdfm test.dvi \
open test.pdf # MacOS X runs my pdf in preview
---
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Re: [Haskell-cafe] MPFR / FFI - Nefarious (Simple?) bug
If you substitute your mpfr_set_signed_int for the one below, the noworks should become works. Yes, this works perfectly. Thank you for saving my project! (Had I known about HMPFR when I started this project, I would have just used that instead of rolling my own, but it looks like HMPFR was uploaded at the end of September though I started rolling my own bindings in June or July... you know how life goes: work, moving, vacation, wife starting grad school, etc.) Last night I was seriously considering dropping work on my current project and joining the effort to replace GMP in GHC as the only solution. But now I Thanks, Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] MPFR / FFI - Nefarious (Simple?) bug
In order to create an arbitrary precision floating point / drop in
replacement for Double, I'm trying to wrap MPFR (http://www.mpfr.org/)
using the FFI but despite all my efforts the simplest bit of code
doesn't work. It compiles, it runs, but it crashes mockingly after
pretending to work for a while. A simple C version of the code happily
prints the number 1 to (640 decimal places) a total of 10,000 times.
The Haskell version, when asked to do the same, silently corrupts (?)
the data after only 289 print outs of 1.... and after 385
print outs, it causes an assertion failure and bombs. I'm at a loss
for how to proceed in debugging this since it should work.
The code can be perused at http://hpaste.org/10923 (and attached) and
downloaded at http://www.updike.org/mpfr-broken.tar.gz
I'm using GHC 6.83 on FreeBSD 6 and GHC 6.8.2 on Mac OS X. Note you
will need MPFR (tested with 2.3.2) installed with the correct paths
(change the Makefile) for libs and header files (along with those from
GMP) to successfully compile this.
Why does the C version work, but the Haskell version flake out? What
else am I missing when approaching the FFI? I tried StablePtrs and had
the exact same results.
Can someone else verify if this is a Mac/BSD only problem by compiling
and running my code? (Does the C executableworks work? Does the
Haskell executable noworks not work?) Can anyone on Linux and
Windows attempt to compile/run and see if you can get the same
results?
Jared.
P.S. I actually have much more code, having wrapped dozens of
functions from the MPFR library and created instances using
unsafePerformIO and foreignPtrs and all that useful high level
Haskell/pure stuff--- all of which basically works perfectly except
that it doesn't work at all since it crashes mysteriously after
pretending to work at first. I had to narrow it down to something
simple and the Print 1.0... 10,000 times was the best I could
do. If I can get that working, I will then move on to something like
the factorial of 1000 (printing intermediate values), which also works
in C, but not Haskell, and after that, maybe everything will just
work and I can use/publish this library!
- works.c
#include stdio.h
#include stdlib.h
#include string.h
#include gmp.h
#include mpfr.h
#include mpfr_ffi.c
int main()
{
int i;
mpfr_ptr one;
mpf_set_default_prec_decimal(640);
one = mpf_set_signed_int(1);
for (i = 0; i 1; i++)
{
printf(%d\n, i);
mpf_show(one);
}
}
Main.hs --- Doesn't work!
module Main where
import Foreign.Ptr( Ptr, FunPtr )
import Foreign.C.Types( CInt, CLong, CULong, CDouble )
import Foreign.StablePtr ( StablePtr )
data MPFR = MPFR
foreign import ccall mpf_set_default_prec_decimal
c_set_default_prec_decimal :: CInt - IO ()
setPrecisionDecimal :: Integer - IO ()
setPrecisionDecimal decimal_digits = do
c_set_default_prec_decimal (fromInteger decimal_digits)
foreign import ccall mpf_show
c_show :: Ptr MPFR - IO ()
foreign import ccall mpf_set_signed_int
c_set_signed_int :: CLong - IO (Ptr MPFR)
showNums k n = do
print n
c_show k
main = do
setPrecisionDecimal 640
one - c_set_signed_int (fromInteger 1)
mapM_ (showNums one) [1..1]
-- mpfr_ffi.c
// a little bit of wrapper code... this may be where the problem is
// but since the (working) C code uses this and has no problems, I don't
// understand why the Haskell code appears to be corrupting the limbs
(the mantissa)
#include stdio.h
#include stdlib.h
#include string.h
#include gmp.h
#include mpfr.h
void mpf_show(mpfr_ptr x)
{
mpfr_out_str(stdout, 10, 0, x, GMP_RNDN);
printf(\n);
}
#define LOG2_10 3.3219280948873626
#define IEEE_BITS 53
void mpf_set_default_prec_decimal(int dec_digits)
{
double bits = LOG2_10 * dec_digits;
int ibits = (int)bits;
double ddec;
int dec;
//printf(DEC_DIGITS = %d\n, dec_digits);
//printf(IBITS = %d\n, ibits);
ddec = ibits / LOG2_10;
dec = (int)ddec;
//printf(DEC= %d\n, dec);
while (dec dec_digits)
{
ibits++;
//printf(IBITS = %d\n, ibits);
ddec = ibits / LOG2_10;
dec = (int)ddec;
//printf(DEC= %d\n, dec);
}
mpfr_set_default_prec(ibits);
}
mpfr_ptr mpf_new_mpfr()
{
return (mpfr_ptr)malloc(sizeof(__mpfr_struct));
}
mpfr_ptr mpf_set_signed_int(int x)
{
mpfr_ptr result = mpf_new_mpfr();
if (result == NULL)
return NULL;
mpfr_init_set_si(result, x, GMP_RNDN);
return result;
}
--- Makefile
CC = gcc
HC = ghc
INCLUDE = -I/home/private/local/include -I/usr/local/include
-I/opt/local/include
LIBS= -L/opt/local/lib -L/usr/local/lib
all:works noworks
works: mpfr_ffi.o works.o
$(CC) -o works works.o -lgmp -lmpfr $(INCLUDE) $(LIBS)
works.o:works.c
$(CC) -c works.c $(INCLUDE)
Re: [Haskell-cafe] MPFR / FFI - Nefarious (Simple?) bug
Thanks for trying out my code. I'm glad it's not particular to my system. I suspected it had to do with the GHC RTS monkeying around with the heap (lower precisions print more iterations and maybe aren't moving through the heap as fast?) but I think when I added a statement to print out the hex address for each Ptr MPFR that those pointers (to 'one') in particular weren't getting moved. Likely the stuff living in the heap, pointed at in the MPFR struct, specifically the pointer to the limbs (the mantissa or actual digits of the number) are getting kludged.. I don't really understand why this is the case when I don't think I'm allocating a lot of the heap or anything, just printing the same number over and over... Is there a space leak somewhere? (I can also verify that mpf_new_mpfr is only getting called once per program run by appending to a file each time it gets called). How do I tell GHC leave this mess and anything in the C heap completely alone? Jared. On 10/5/08, Alexander Dunlap [EMAIL PROTECTED] wrote: On Sun, Oct 5, 2008 at 5:38 PM, Chris Mears [EMAIL PROTECTED] wrote: Jared Updike [EMAIL PROTECTED] writes: Can someone else verify if this is a Mac/BSD only problem by compiling and running my code? (Does the C executableworks work? Does the Haskell executable noworks not work?) Can anyone on Linux and Windows attempt to compile/run and see if you can get the same results? I can't help you fix the problem, but can confirm that it behaves as you describe on my Linux system. The program works produces correct output, but noworks gives: == [...] 290 1.0 291 1.00315821571076304370386829039486164636536120569099678825575157477354990710405658927062619547595122867857873765133026050519075772712996650488675128428778696175272153632855303857710094714398932056909218681833163883482512398576534211955878126971368731378321605715030861892325510831739618679352919703855747262870175016933079782350322237289103929997053812694251557912158924211585973481445271933347978517620 292 [...] 384 1.00315821571076304370386829039486164636536120569099678825575157477354990710405658927062619547595122867857873765133026050519075772712996650488675128428778696175272153632855303857710094714398932056909218681833163883482512398576534211955878126971368731378321605715030861892325510831739618679352919703855747262870175016933079782350322237289103929997053812694251557912158924211585973481445271933347978517620 385 1.00315821571076304370386829039486164636536120569099678825575157477354990710405658927062619547595122867857873765133026050519075772712996650488675128428778696175272153632855303857710094714398932056909218681833163883482512398576534211955878126971368731378321605715030861892281684860507747503219323326708248193093246881500522519352192987169395899758472958160241015525770811984166890239749344848735134541218 386 ../get_str.c:149: assertion failed: size_s1 = m Aborted == All the values from 291-384 are the same, but 385 is slightly different. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe My results (from Linux i686) are slightly different. I am getting [...] 287
Re: [Haskell-cafe] Slow IO
Maybe I've misused the word segfault. What happened is: The programme consumed more and more memory (according to top), kswapd started to have a higher CPU-percentage than my programme, programme died, system yelling 'Speicherzugriffsfehler', top displays 'kswapddefunct'. I believe that means my programme demanded more memory than I have available (only 256MB RAM + 800MB swap). Is that a segfault or what is the correct term? I thought a segfault was when a program reads or writes to protected memory (for example, out of bounds on an array, or dereferencing a null pointer, etc. things mostly avoided in Haskell). Luckily there are lots of fun ways to crash computers! I've heard your heap overflow called exploding because of how the process rapdily expands its memory usage, filling all available space, causing system collapse. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] map (-2) [1..5]
In C, it wouldn't be, since there, unary ops always bind tighter than infix ops, and the precedences used in C are also used in C++, Java, C#, Javascript etc, and even ISO Prolog obeys the rule that unary minus binds tighter so making unary minus have the same precedence as infix minus just makes Haskell syntax difficult to parse for anyone coming from one of these other very popular languages. Imho, for better or worse, C has established a kind of de-facto standard that unary ops always bind tighter than infix ops in programming languages ;-) ... in **programming languages that don't have infix exponeniation**. You missed Ruby, Python, Matlab, Mathematica (not generally a good inspiration for syntax but it has a rather large following and almost 20 years of usage), and TI calculators. These all have ^ or ** bind tighter than unary - to go along with math, not C. Since it didn't happen we will never know **if C had had infix exponentiation, what would the precedence have been relative to unary ops** or indeed if they dropped infix exponentiation, preferring pow(x,y), for exactly that reason, or what. All this talk is a design choice and folks will naturally disagree and the right balance for *everything*, especially since all their conflicting interactions yield so many mutually exclusive possible outcomes. I suppose I just disagree that C has said the last word about infix/unary ops because C never spoke up on the problem of unary negation and exponentiation. (And if it had, would I agree anyway? :-) I still get tripped up by unary negation in Haskell, especially with sections, parenthese, etc. But that's what hugs or ghci are for. Also, it's a good example of why we should *not* have unary minus, since the above could be written with no ambiguity as: negate (4 ^ 2) or better still: negate (expNat 4 2) because this would free the ^ symbol for some more widely applicable use, True. I would much rather be forced to type negate (4 ^ 2) than have -4^2 return 16 instead of -16 because the - got lexed into -4. Alternately, if you want unary ops to bind the tightest, then just eliminating ^ and replacing it with expNat, etc. would solve any precedence problems with unary minus. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] head as a total function
it was the first imperative language supporting closures, after all Uh, what about lisp? For those who read the Foozles slides posted earlier [0], I must say he nailed this one, on slide 2. The (MIT) lisp 1.4 manual (ca. 1965) refers to FUNCTION differing from QUOTE in that it handled free variables correctly; I take this to mean that at least a primitive form of closure was provided. Steele's work on Scheme helped Lisp programmers take lexical scoping seriously [1]; these ideas and a method for efficient implementation were attributed to Algol [2]. That lexical scope was available in some dialect of Lisp, even very early on, doesn't surprise me (and according to [3] is the case). But I do think dynamic scoping took a while to die out as generally accepted Lisp practice (it does still exist in Common LISP, with a special keyword, IIRC) and that Scheme (late 1970s) helped to effect that. Moreover, a language that provides SET/SETQ, RPLACA/RPLACD and the PROG feature (including labels and a goto) surely qualifies as imperative? Haskell has been called the best imperative programming language ever. :-) I mean, Haskell has IORef and friends, right? Jared. [0] http://hope.cs.rice.edu/twiki/pub/WG211/M3Schedule/foozles.pdf [1] Tenth paragraph, this page: http://www.lisp.org/table/Lisp-History.html [2] Steele's Rabbit compiler paper, p.13. See also Steele's Lambda papers [3] Steele and Gabriel, Evolution of Lisp. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Re: data structures question
And stop calling me Shirley. Could you please be a bit more explicit? Have I offended anyone? This is a reference to a joke from the movie Airplane: Surely, you can't be serious. I am serious, and stop calling me Shirley. I imagine it meant nothing personal. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to force HTML (rather than XML) output from Haskell XML Toolbox?
which is close but not exactly as wanted. The meta (and I expect other tags like br will have the same) tag has closing slash as it would have in XML (XHTML), but not in HTML. Also the DOCTYPE has been lost. I've had similar problems outputting XHTML. For example, naive output (correct according to the definition of XML and (X)HTML) breaks in IE because IE doesn't like link ... / or script ... / tags, instead it wants link .../link and script .../ script. Pages with correct XHTML, but with these unhappy tags in the HTML head, load in IE as a blank page! To make pages that will load in 90% of browsers, I've always generated my own (X)HTML with special pretty printers that know these caveats and a few others. Jared. On 8/30/06, Dimitry Golubovsky [EMAIL PROTECTED] wrote: Hi, I am developing a code that reads a HTML page (template), modifies it (adds some stuff) and then writes the output file which is to be HTML, not XML. I use hxt-5.3 (but I may upgrade if necessary). It is desired to preserve the original HTML template pieces maximally close to the original. But output appears to be closer to XML rather than HTML. The code I use: let attrs = [(a_parse_html, 1), (a_output_xml, 0), (a_encoding, utf8)] (res, err, rc) - getXmlDocument attrs (fromJust $ tmplPath dopt) putXmlDocument attrs (fromJust $ outPath dopt) res = for this input HTML file: = !DOCTYPE html PUBLIC -//W3C//DTD HTML 4.01 Transitional//EN html head titleEmpty Page Template for Haskell Applications/title meta http-equiv=content-type content=text/html; charset=UTF-8 /head body /body /html = outputs: = html head titleEmpty Page Template for Haskell Applications/title meta http-equiv=content-type content=text/html; charset=UTF-8/ /head body /body /html = which is close but not exactly as wanted. The meta (and I expect other tags like br will have the same) tag has closing slash as it would have in XML (XHTML), but not in HTML. Also the DOCTYPE has been lost. Is this something hxt is not able to provide, or just a bug fixed since 5.3? Or should I write my own output code (because I am guessing, hxt functionality regarding manipulation over XML trees is sufficient for what I need)? Or should I use another package? -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to force HTML (rather than XML) output from Haskell XML Toolbox?
Just a bit of info on the br, IE treats br/ as a line break, but br/br as 2 line breaks. Just in case you go for the obvious solution of always expanding out a/ to a/a, br won't work. but br / with a space works. And this applies to most tags with this behavior---the space helps, and it validates with W3C XHTML Validator. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fran - Functional Reactive Animation
I think this works: http://haskell.org/edsl/pansharp.html Jared. On 8/23/06, HIGGINS Neil (ENERGEX) [EMAIL PROTECTED] wrote: Fran is a Haskell library (or embedded language) for interactive animations with 2D and 3D graphics and sound. See http://www.conal.net/fran/ and http://research.microsoft.com/research/downloads/download.aspx?FUID=c9eff407-ce59-4a2a-90cb-de099a9bacbd I would like to use Fran as a rapid prototyping environment for animations, but it appears to be broken under WinHugs. I'm looking for someone with much better Haskell prowess than myself who might be able resurrect Fran under WinHugs. Unfortunately I can only offer my gratitude in return. It's a long shot, I know. Kind regards, Neil Higgins Snr Strategic Planning Engineer ENERGEX Em: [EMAIL PROTECTED] Ph: 3407 4800 Fx: 3407 4832 * This email message (including any file attachments transmitted with it) is for the sole use of the intended recipient(s) and may contain confidential and legally privileged information. Any unauthorised review, use, alteration, disclosure or distribution of this email (including any attachments) by an unintended recipient is prohibited. If you have received this email in error, please notify the sender by return email and destroy all copies of the original message. Any confidential or legal professional privilege is not waived or lost by any mistaken delivery of the email. ENERGEX accepts no responsibility for the content of any email which is sent by an employee which is of a personal nature. Sender Details: ENERGEX GPO Box 1461 Brisbane QLD Australia 4001 +61 7 3407 4000 http://www.energex.com.au ENERGEX policy is to not send unsolicited electronic messages. Suspected breaches of this policy can be reported by replying to this message including the original message and the word UNSUBSCRIBE in the subject. * ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] implementing a csv reader
Now I need to find something else for practice. Is there anything related to data analysis/statistics that is lacking is Haskell? A native implementation of multiparameter data fitting (requires some linear algebra) like: Sec 15.4 of http://www.library.cornell.edu/nr/bookcpdf.html or http://www.gnu.org/software/gsl/manual/html_node/Multi_002dparameter-fitting.html#Multi_002dparameter-fitting would be nice, unless it exists. (There might be a GSL binding in Haskell for this but I'd rather use a native library.) Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Memoizing longest-common-subsequence
(Sorry for the late reply; have been on holiday.) No problem. Your email system was kind enough to say when you'd be back :-) I've used it to diff fairly large files (hundreds of K's, if not Megs) where there were few differences. It seemed to perform OK, and in cases where GNU diff (or whatever comes with MSYS) failed. Thanks for posting the code. It works on pretty large data sets (for example, a thousand Strings each) and I have a hunch that if I use Data.ByteString it would even work fast enough on my quarter meg text files (split on words, ~40,000 and ~50,000 words each) to use in place of GNU sdiff or diff. Did you use FastPackedString or ByteString to get performance you alluded to? I'll return with the results of my experiments with ByteString and Diff, although I imagine it should be pretty fast since darcs is able to get acceptable speed on large datasets using (I think) ByeString and a Haskell implementation of Myers diff. Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell wiki: most popular pages
I feel that Haskell is missing some basic string manipuation functions, like - replacing all occurances of one substring (or sublist) with another string (or list). - tokenize a string by an arbitrary delimeter This came up not too long ago: http://www.haskell.org/pipermail/haskell-cafe/2006-July/thread.html#16559 Ironically this thread talks about how the same topic came up two years ago and no consensus was reached. So I made a skeleton page to discuss/maybe reach consensus on this. Please flesh it out and hack it to pieces! http://www.haskell.org/haskellwiki/Prelude_function_suggestions I know many of these functions can be written in Haskell without much effort. Let the work begin (record opinions and any semblance of consensus). Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] map (-2) [1..5]
I'd have thought it would have been simpler to just make the rule that -2 (no spaces between '-' and '2') would be a single lexeme I'd have thought so too, until I implemented a parser with exponentiation. It is easy to get confused and make a parser that is too eager to include the minus sign as part of a numeric literal instead of as subtraction or unary negation (all you parser-with-exponentiation-implementers out there, pay attention!). And since many programming languages (specifically C) don't have syntax for exponentation as an infix operator (nothing authoritative to copy precedence from), I had to implement this myself, get confused and see that it was so---(I tried making the literal include the minus sign if there was no space). I never noticed this before because in a C-like language: -4*2is the same whether parsed as (-4)*2 or -(4*2) but -4^2is not the same whether parsed as (-4)^2 or -(4^2) (the correct version) Basically, before someone argues this with me, -4^2 should parse the same as - 4^2 which should be the same thing as 0 - 4^2 (you don't want -4^2 and 0-4^2 giving different results, no matter how much you think whitespace belongs around operators) Math follows these same rules but it's slightly harder to get confused because of the way exponentiation is written by superscripting. See http://mathforum.org/library/drmath/view/55709.html and http://mathforum.org/library/drmath/view/53240.html. I thought this was surprising, that parsing the minus sign into lexemes would cause such confusion, but it is born out in many places (Python, Frink (http://futureboy.homeip.net/frinkdocs/FrinkApplet.html), etc.) (Note: this email isn't about Haskell specifically and I'm sure issues with the minus sign in Haskell are more confusing than this; this is purely about parsing a C-like langauge extended with exponentionation and how including the minus sign in the literal is dangerous in conjuntion with exponentiation.) Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] map (-2) [1..5]
I'd also argue that in maths the necessary brackets are implied by the superscripting syntax ASCII text parsing issues aside, in math, 2 -4 =? (No you cannot ask if there is space between the 4 and the - symbol, or if I meant (-4)^2 or -(4^2), or if I wrote a negative sign or a subtract sign. I believe there is only one standard interpretation here.) they can only get in through the back door of evaluation which just doesn't seem right. Constant folding can eliminate any runtime cost, so effectively 0 - 2 == negative 2 at compile time. No problem. Jared -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] map (-2) [1..5]
Yes but my point is that -4^2 is not the same as 2 -4 because the latter by convention means - (4^2). In other words, superscripts bind tighter than prefix ops but prefix ops bind tighter than infix. I see. My point is that there already exists a convention[1] that the way to type in 2 -4 is -4^2 which means -(4^2) not (-4)^2 because - as a prefix op has the same precedence as binary subtraction, not super tight like normal prefix ops (i.e. normal function application) as you would like it to be (if I understand correctly). You are welcome to break an existing (unofficial) convention for the sake of lexical syntax[2]. Cheers, Jared. [1] On my TI89 calculator (where there are even two - buttons: a little negative unary button and a binary subtract button). It pretty prints 2 -4 = -16 when I punch in -4^2 (where - is the negative unary button). The answer is -16. Python (-4**2 = -4 ** 2 = - 4 ** 2 = -16) and Matlab and Mathematica agree (-4^2 = -4 ^ 2 = - 4 ^ 2 = -16). [2] http://wadler.blogspot.com/2006/01/bikeshed-coloring.html -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Int-[Char] conversion
putStrLn (Product: ++ convertnumbertostring(pp)) Also, there is a predefined function called 'print' where print x = putStr (convertnumbertostring x) i.e. print x = putStr (show x) Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can someone explain this typing restriction?
Google Scholar is often quite handy for this sort of situation. http://scholar.google.com/scholar?q=typing-haskell-in-haskell+jones Jared. On 8/14/06, Tim Walkenhorst [EMAIL PROTECTED] wrote: It can be found here: http://citeseer.ist.psu.edu/424440.html Thanks! Actually I've seen this page before, but was too retarded to figure that you can access the actual document there. I thought it was just an abstract... (*embarrassed*) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] AJAX applications in Haskell
http://happs.org/HAppS/README.html http://pass.net/ Jared. On 8/9/06, Adam Peacock [EMAIL PROTECTED] wrote: On 8/10/06, Jared Updike [EMAIL PROTECTED] wrote: [..] http://www.ugcs.caltech.edu/~lordkaos/calc.cgi (source available here http://www.ugcs.caltech.edu/~lordkaos/calc.tar.gz) I've only recently joined this mailing list, and there seems to be a considerable amount of talk about Haskell and web applications. Although I can't seem find any commercial sites using Haskell. I'm not after examples like the WASH gallery, I'm after non-trivial, real or commercial applications using Haskell and the web. Does anyone know of any? Adam. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Memoizing longest-common-subsequence
and also ended up with an STArray based implementation. I can send the code if you're interested. I have no idea how well it performs compared to Ian's, or the one in darcs (which uses PackedStrings). Ian's LCS code looks like it works fine in terms of space usage, but for large input (lengrh as == 4, length bs == 5) it seems to be way too slow in terms of time complexity (GNU sdiff executes on this same data in a few seconds, the Hunt-Szymanski LCS algorithm didn't terminate, even after like 10 minutes). If it's not too much trouble, could you send Myers STArray based code? Thanks, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] AJAX applications in Haskell
This would require to: - Retarget one of the existing Haskell compilers to generate JavaScript (other possible targets would be Flash or higher level UI languages such as OpenLaszlo that in turn compiles down to either Flash or JavaScript/HTML) As I've noticed from experience, you can just write JavaScript itself! (You will end up doing this a lot anyway because any library is bound to be missing some feature you need, say, input textbox history w/ up/down keys, or, say, autoscroll to bottom of iframe when content added, etc. as here): http://www.ugcs.caltech.edu/~lordkaos/calc.cgi (source available here http://www.ugcs.caltech.edu/~lordkaos/calc.tar.gz) Is anyone working on anything similar or that might be interested in such a project? I'm definitely interested in this. I would love to be able to deploy a Haskell application in the web browser w/out having to drain server computing resources. Imagine reading a Haskell tutorial and providing interactive applications that run in the reader's browser, etc. Also, I really would love to see something in Haskell that can compete with the Web Services / Web Forms stuff from Visual Studio 2005/C# in terms of simplicity and power and feature-completeness: just write your app and it generates all the HTML/CSS/JavaScript on the client and the XML request stuff on the serve. Perhaps in Haskell we could have something fugdets-like but deployable in any (relatively recent) browser w/ no downloads. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can Your Programming Language Do This?
So basically he rediscovered Why FP Matters (http://www.math.chalmers.se/~rjmh/Papers/whyfp.html) ~15-20 years after the fact, but neglected to point out the interesting fact that one can write map in terms of reduce (i.e. foldr) (obviously he didn't read the paper) and ignored the benefits of laziness. Also, if your programming language has this ability and it's so great, why is this not idiomatic? (i.e. people using for loops all over the place in JavaScript). (Sorry, couldn't find a place to comment on Joel's blog). Jared. On 8/2/06, Stephane Bortzmeyer [EMAIL PROTECTED] wrote: From the excellent programming blog Joel on software, a very good text if you need to convince Java or C programmers that functional programming is a A Good Thing. Probably all the readers of this list will find it brings nothing new (that's perfectly right) but it is oriented towards ordinary programmers :-) http://www.joelonsoftware.com/items/2006/08/01.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can Your Programming Language Do This?
I don't think this commentary is really fair. It's also insular and bad for the reputation of the Haskell community. There are enough barriers to exploring FP and Haskell already. The purpose of the article was to encourage people to start taking baby steps toward FP, not to demonstrate a deep mastery of the subject. I feel (maybe others agree) delighted that someone so widely read begins to extoll the virtues of functional programming. I also feel (maybe others also agree) disappointed that this, and other such articles, fail to take the subject far enough, really showing what better programming languages can do. I supposed I should be happy; the long road to FP has to start somewhere, hopefully others will start down that road sooner rather than later. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Memoizing longest-common-subsequence
On 8/1/06, Mark T.B. Carroll [EMAIL PROTECTED] wrote: I wanted a longest common subsequence function and a bit of Googling failed to turn up a functional one, except for in a scary bit of darcs. I saw a thread from back in the day about this when I was looking for a good implementation of sdiff (or diff) in Haskell (thank Googleness for Google): http://www.haskell.org/pipermail/haskell/2002-November/010731.html all message in thread: http://www.haskell.org/pipermail/haskell/2002-November/thread.html#10726 Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Future Edison directions
This page: http://jaortega.wordpress.com/2006/03/17/programmers-go-bananas/ lists some references at the bottom. Perhaps they would be useful. Jared. On 8/1/06, Brian Hulley [EMAIL PROTECTED] wrote: Robert Dockins wrote: [snip other points] 7) Finally, I somehow feel like there should be a nice categorical formulation of these datastructure abstractions which would help to drive a refactoring of the API typeclasses in a principled way, rather than on an ad-hoc I-sort-of-think-these-go-together sort of way. Unfortunately, my category-fu is quite weak, so all I have is this vague intuition that I can't substantiate. I'm sort of familiar with initial algebras, but I think they may be too concrete. I'm looking for some way to classify algebras that have, eg, the property of having folds, or of being set-like, etc. If anybody can point me in the right direction wrt this, that would be great. I'd love to find out more about these categorical abstractions also, since Monads and Monoids (the only ones I know about) are an incredible source of power and expressiveness in Haskell programming, so I've got the feeling that I'm wasting tremendous amounts of time reinventing the wheel when other abstractions that may be equally useful are just waiting to be used... Can anyone recommend a good book or web tutorial about category theory that's not too difficult? I'm thinking about something which would have lots of diagrams and discussion about the relevance of the concepts to practical computing problems but not something loaded with complicated proofs or LaTeX symbols :-) Thanks, Brian. -- Logic empowers us and Love gives us purpose. Yet still phantoms restless for eras long past, congealed in the present in unthought forms, strive mightily unseen to destroy us. http://www.metamilk.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Trouble compiling wxhaskell
Hmmm I found http://www.haskell.org/haskellwiki/WxHaskell/Installation_tips so there are two such pages, the other being: http://www.haskell.org/haskellwiki/WxHaskell/Install so perhaps these pages can be merged? and a redirect placed from one to the other? Cheers, Jared. On 7/31/06, Jason Dagit [EMAIL PROTECTED] wrote: I've done this recently. I put my notes on the wiki: http://www.haskell.org/haskellwiki/WxHaskell/Install#Windows Do you have a particular error message? Jason On 7/31/06, David F. Place [EMAIL PROTECTED] wrote: Hi: I'm having trouble compiling wxhaskell 0.9.4 under both ghc 6.4.2 and ghc 6.5. Does anyone know where I should direct my queries? Thanks. David F. Place mailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie Q: Deriving MyOrd from Eq problem
I am trying to derive MyOrd class from Eq (Prelude): class Eq a = MyOrd a where (%=), (%), (%=) :: a - a - Bool x %= y = (x y || x == y) x % y = y x x %= y = (y x || x == y) Q: What's wrong? Why 'Ord' gets into play here? You are using which is a function on types that instance the class Ord, so the compiler is telling you to add (Ord a) to the same place you have (Eq a) or don't use or or any function in the class Ord. You can the prelude and thus the Ord class and make your own and functions but you can't make them refer to the real and functions without Ord because that is where they live. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie Q: Deriving MyOrd from Eq problem
Sorry, left out an important verb, *hide*: You can the prelude and thus the Ord class and make your own and You can *hide* the prelude and thus the Ord class and make your own and Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Haskell?
GSL Haskell bindings: http://dis.um.es/~alberto/GSLHaskell/ http://dis.um.es/~alberto/GSLHaskell/doc/ Specifically for Linary Algebra: http://dis.um.es/~alberto/GSLHaskell/doc/GSL-Base.html You make a good point and the decision was by no means cut and dry. However I made a point of developing some test code using some the newer array data types and looked at maintaining the array in Haskell and then directly calling Blas etc. I even had a nice polymorphic matrix class going. However I found the array interface just a bit too 'clunky' to use a technical term. The withArray interface is not very appealing. The layers of lambda notation was giving me a headache. I think part of the problem here is not necessarily C or Haskell's fault, but rather that what you were trying to do was write a library (or needed the right library). Library writing is hard enough on its own, much less when one is relatively new to Haskell! Hopefully you will find the right tool for the job and things will go well! Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] process simulation in functional style
Also, I found that the textbook The Haskell School of Expression by Paul Hudak is a good introduction (particularly, if I remember correctly, the second half of the book) to functional reactive programming in Haskell. Jared. On 7/16/06, Nicolas Frisby [EMAIL PROTECTED] wrote: You might discover helpful techniques by searching for these terms/projects/papers: - functional reactive programming (e.g. Yampa project) - resumption monad (e.g. Cheap but Functional Threads) - concurrent Haskell extensions - or even comonads (e.g. Essence of Dataflow) The activation energy to be invested in each technique is likely considerable, but that's the fun part, right? Hope that helps, Nick On 7/16/06, Alexander Vodomerov [EMAIL PROTECTED] wrote: Hello! I'm writing a program that simulates multiple processes. The processes may send/receive messages, do some work, or sleep for some amount of time. I have seen that many such things can be expressed in Haskell in very elegant manner using it functional or lazy properties. For example, client/server interaction may be expressed via inifinite lists as shown in Gentle Introduction to Haskell. Another way of process simulation is describied in http://citeseer.ist.psu.edu/harcourt95extensible.html, where simple and concise CCS interperter is constructed. I've tried to apply the idea of infinite lists or CCS-style processes, but fail. The main reason is that: 1) messages are asynchronous (it may be received and handled while process are sleeping, without waking them) 2) in some cases received message may wake up process 3) all activity in system is ordered by time 4) there are 2 process and during simulations new processes may be created I've no idea how to implement 1, 2 in CCS interpeter. The approach of infinite lists seems to have problems with 3, 4. Have somebody any ideas how this can be solved in simple and concise way? With best regards, Alexander. PS. Currently I have some code (see below), but it is VERY UGLY. The main drawback is that is very imperative. It employs notion of Global state. It doesn't use features of Haskell and can be rewritten in ML or C++ without changes. Another flaws is that it is very unextensible, and all processes must have the same state. -- example code latency = 0.001 type Message = String type MsgM = WriterT [(Int, Message)] IO -- process may send messages -- process states next id = (id + 1) `mod` 3 type State = (Int, Int, Double) -- proc. number, counter, interval do_step :: State - MsgM (Double, State) --- do something and then sleep do_step (id, cnt, delay) = do tell [(next id, ping ++ show id ++ cnt ++ show cnt)] return (delay, (id, cnt + 1, delay)) handle_message :: Message - State - MsgM State handle_message msg (id, cnt, delay) = do -- liftIO $ putStrLn $ show id ++ received msg ++ msg if msg !! 0 == 'p' then tell [(next id, reply ++ show id ++ to ++ msg)] else return () return (id, cnt, delay) -- global event queue data Event = MsgRecv Message | Work deriving Show type EventQueue = [(Double, Int, Event)] compare_event (t1, n1, e1) (t2, n2, e2) = compare t1 t2 type EventM = WriterT EventQueue IO queue_event :: Int - Event - Double - EventM () queue_event dest ev time = tell [(time, dest, ev)] type FullState = Map.Map Int State handle_event :: Int - Double - Event - FullState - EventM FullState handle_event procnum time ev fullstate = do let localstate = (fullstate Map.! procnum) case ev of MsgRecv msg - do (nstate, messages) - lift $ runWriterT (handle_message msg localstate) sequence_ $ map (\(dst, msg) - queue_event dst (MsgRecv msg) (time + latency)) messages return $ Map.insert procnum nstate fullstate Work - do ((pause, nstate), messages) - lift $ runWriterT (do_step localstate) sequence_ $ map (\(dst, msg) - queue_event dst (MsgRecv msg) (time + latency)) messages queue_event procnum Work (time + pause) return $ Map.insert procnum nstate fullstate run_queue :: FullState - EventQueue - IO () run_queue st eventqueue = case eventqueue of [] - return () (time, dest, ev) : rest - do putStrLn $ processing event ++ (showFFloat (Just 3) time) ++ at procnum ++ show dest ++++ show ev (nst, nev) - runWriterT (handle_event dest time ev st) let nqueue = foldl (\res - \e - insertBy compare_event e res) rest nev run_queue nst nqueue init_state = Map.fromList [(0, (0, 0, 0.3)), (1, (1, 0, 0.4)), (2, (2, 0, 0.5))] main = run_queue init_state [(0, 0, Work), (0, 1, Work)] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___
Re: [Haskell-cafe] Type of a function?
Did you try putting this in a file, say, t.hsand running ghci t.hs then typing :type func at the GHCi prompt? It should tell you the function type. Jared. On 7/14/06, Jenny678 [EMAIL PROTECTED] wrote: Hallo Can somebody tell me the type of the following function? func :: ? func f x = (z,y) where (z,y) = f x Thanks -- View this message in context: http://www.nabble.com/Type-of-a-function--tf1945843.html#a5335607 Sent from the Haskell - Haskell-Cafe forum at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type of a function?
(leave off the line with func :: ??? and the compiler will figure it out for you, if possible---it works in this case) Jared. On 7/14/06, Jared Updike [EMAIL PROTECTED] wrote: Did you try putting this in a file, say, t.hsand running ghci t.hs then typing :type func at the GHCi prompt? It should tell you the function type. Jared. On 7/14/06, Jenny678 [EMAIL PROTECTED] wrote: Hallo Can somebody tell me the type of the following function? func :: ? func f x = (z,y) where (z,y) = f x Thanks -- View this message in context: http://www.nabble.com/Type-of-a-function--tf1945843.html#a5335607 Sent from the Haskell - Haskell-Cafe forum at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why is there no splitBy in the list module?
fields = csv `separateWith` , csv = fields `joinWith` , -- equivalent to concatIntersperse Hence I would much rather have the split condition be the first parameter -- the infix notation looks good, but it will need a flip to get the parameters in the right order. This also goes along with join in python, i.e. \n.join(xs) == \n `join` xs in Haskell (wherejoin sep = concat . intersperse sep ) Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why is there no splitBy in the list module?
split is... unconcatIntersperse. How about separate? (split or splitBy is better but it is used all over the place in many libs) And for strings I definitely would use split :: [a] - [a] - [[a]] a lot, just like Python's split function. And words works great for breaking on multiple spaces, so I would avoid trying to fill that need... Jared. Hmm... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] closures with side effects
I have been trying to understand closures in haskell and how they relate to side effects. I have been looking around but all I find are trivial examples with no side effects. Please let me know if you know of any examples. Bulat what you mean by 'closure'? Perhaps you are refering to something like the Accumlator generator in Lisp: (defun mkacc (n) (lambda (i) (incf n i))) or Scheme: (define (mkacc n) (lambda (i) (set! n (+ n i)) n)) (the term closure explained in footnote 6 in SICP here: http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-15.html#footnote_Temp_154: A closure is an implementation technique for representing procedures with free variables.) ? In Haskell you can do this, but all side effects are made explicit and can only be used within code marked with IO (in the IO monad): import Data.IORef mkAcc :: (Num a) = a - IO (a - IO a) mkAcc n = do r - newIORef n return (\i - do modifyIORef r (+i) readIORef r) (These examples are from http://www.paulgraham.com/accgen.html, by the way.) On 6/26/06, dkarapet [EMAIL PROTECTED] wrote: I have been trying to understand closures in haskell and how they relate to side effects. I have been looking around but all I find are trivial examples with no side effects. Please let me know if you know of any examples. in Haskell, expression may have a side effect only if it has IO a return type. it is then whole point of pure lazy language - evaluation of pure (not IO) expression can be deferred until it's value really need and language guarantee that this don't change anything (including lack of any side effects) Bulatmailto:[EMAIL PROTECTED] The reason you need IO in the type that the compiler/type system forces you to isolate side effects from pure code so all your pure code stays pure. There is a good explanation here, under Pure Functions: http://en.wikipedia.org/wiki/Functional_Programming#Pure_functions The reason purity is **enforced** is similar to the reason goto is considered harmful: the belief is that the programmer receives great benefits this tradeoff. In exchange for giving up side effects in arbitrary places, the programmer gains freedom in knowing that all pure functions are free from side-effects related bugs and her code is easier to reason about mathematically. My understanding is that Haskell's execution model is a lot more involved than, say, Scheme, because pure code is more flexibly refactored by the compiler and because the runtime evaluation strategy for lazy evaluation is less obviously implemented. In this sense, if I undertsand correctly, Haskell doesn't really use closures as an implementation strategy (as defined above), if that is what your question is refering to, and I'm not surprised that you don't find interesting examples in Haskell, especially any involving side effects. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Eager Parser Combinators [was: Functional programming for processing of largeraster images]
On 6/22/06, Greg Buchholz [EMAIL PROTECTED] wrote: Ralf Hinze wrote: Also, in a non-strict language recursive definitions are not limited to function types. Users of parser combinators heavily rely on this feature. Just try to define/use parsing combinators ins a strict language. Anyone care to comment on what goes wrong with parser combinators in an eager language? Is it mainly a space usage problem (where the lazy version might essentially perform a depth-first-search, while the eager version is breadth-first)? Or is there something else I'm missing? Slide 22 (Combinator Libraries) of http://research.microsoft.com/~simonpj/papers/haskell-retrospective/ shows that in an eager language, you have to make the argument explicit, which destroys the Parser abstraction. Indeed I rolled my own sort of monads and made my own parser combinators in C# and they were a lot like your Perl combinators: very imperative and verbose (~10x more code than Haskell for the same parser), instead of clean and declarative like BNF or Haskell parser combinators. Jared. As a reference, back when I was trying to understand monads, I ported the parser combinators from the Hutton and Meijer paper to perl... http://sleepingsquirrel.org/monads/parser/monad_parser.txt Thanks, Greg Buchholz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Functional progr., images, laziness and alltherest
Therefore the list of non-negative integers is longer than the list of positive integers. I agree they have the same cardinality but this doesn't mean they have the same length. Are you saying that some of the (0,1,2,3,4,5,...), (1,2,3,4,5,...) and (1-1,2-1,3-1,4-1,5-1,...) lists have different lengths? Q: Which list is longer, [0..] or [1..] ? A: MU! (see http://en.wikipedia.org/wiki/Mu_%28negative%29 ) I am un-asking the question. They don't have length. Length only makes sense for lists with [] in them and infinite lists do not use []. Jared. P.S. If you still don't believe me, this code should put this mystery to rest: length2 x y = f 0 0 x y where f a b [] [] = (a, b) f a b [] (y:ys) = f a (b+1) [] ys f a b (x:xs) [] = f (a+1) b xs [] f a b (x:xs) (y:ys) = f (a+1) (b+1) xs ys length2 [0..] [1..] Feel free to get back to us with the results! -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Polymorphic type
On 6/22/06, Sara Kenedy [EMAIL PROTECTED] wrote: Hello all, Now I am trying with the function of polymorphic type: This function returns the Nth element of list with type a. I try it as below. getNthElem :: Int - [a] - Maybe a getNthElemt _ []= Nothing getNthElem 0 _ = Nothing getNthElem n s | n length s = Nothing | otherwise = Just ((drop (n-1) (take n s))!!0) getNthElem 2 [a,b,c] Just b However, I do not satisfy with this function because I want to return the Nth element of type a, not (Maybe a). For example, I want this function: getNthElem :: Int - [a] - a But, I do not know how to define the empty element of type a. Not all types (especially numbers) have an empty element (what does that even mean?). Suppose you have a list [0, 1, -2, -1, 2] and you try getNthElemt 4 and your program assumes that the empty element for integers is 0. How can you tell that 0 from the 0 at the beginning of the list [0, 1, 2]? Think really hard about what you are asking and you will see why Maybe a takes the type a and extends it, in a way, with an empty element, Nothing. To convert it from Maybe a to a, try, e.g. fromJust (Just 4) 4 (it will give exceptions when Nothing shows up). getNthElemt _ []= getNthElem 0 _ = One possiblity is to make a class called empty with a single member: class Empty a where empty :: a instance Empty [a] where -- this also makes= empty for String empty = [] instance Empty Maybe a where -- is this desirable? empty = Nothing instance Integer where -- or this? empty = 0 ... and then add the constraint to your function: getNthElem :: Empty a = Int - [a] - a getNthElem :: Int - [a] - Maybe a getNthElemt _ []= empty getNthElem 0 _ = empty getNthElem n s | n length s = empty | otherwise = ((drop (n-1) (take n s))!!0) but you need overlapping instances to instantiate [a]. Or you could use MonadPlus and mzero instead of Empty and empty, but that would only work for List, Maybe and other monads and not for Integer, etc. Note that in a dynamic language the same thing happens. In python 4 + None raises an exception. I don't think it's possible to get away from this whole failure concept (except silently ignore it---in perl 4+null yields 4 but is that always the right behavior in all situations? It makes bugs really hard to find.) Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple matrix
fromInteger x = [[fromInteger x]] Wouldn't you want the expression [[1,0],[0,2]] + 10 to yield [[11,10],[10,12]] instead of [[11]] ? I guess you would need some complicated machinery so this is one thing you have to ignore to keep your otherwise nifty instance nice and simple. Jared. -- http://www.updike.org/~jared/ reverse )-: abs x = map (map abs) x (+) [ ] y = y (+) x [ ] = x (+) x y = zipWith (zipWith (+)) x y (*) x y = map (matrixXvector x) y where --matrixXvector :: Num a = [[a]] - [a] - [[a]] matrixXvector m v = foldl vectorsum [] $ zipWith vectorXnumber m v --vectorXnumber :: Num a = [a] - a - [a] vectorXnumber v n = map (n*) v --vectorsum :: [a] - [a] - [a] vectorsum [] y = y vectorsum x [] = x vectorsum x y = zipWith (+) x y ___ Novidade no Yahoo! Mail: receba alertas de novas mensagens no seu celular. Registre seu aparelho agora! http://br.mobile.yahoo.com/mailalertas/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple matrix
I dont see how to fix this. There was a thread about statically knowing lots about the shape of matrices using the type system. http://www.haskell.org/pipermail/haskell/2006-April/017845.html I believe they incorporated this (variable size identity matrix, for example) in their approach. (They don't preserve your property of being able to do things with simple list syntax, like [[1,2],[3,4]] * [[5,6],[7,8]] , instead you have to use Template Haskell and some small contructor functions) Could be better to forget about fromInteger... Except then you wouldn't have a full instance for Num. How about constructing an infite list of infinite lists of that number: fromInteger x = map repeat (repeat (fromInteger x)) when it gets zipped with smaller matrices, will it terminate? It works with addition but multiplying caused problems: [[1,2],[3,4]] + 10 = [[11,12],[13,14]] [[1,2],[3,4]] * 10 = [[40,60],[40,60],[40,60],[40,60],[40,60], . Hmm... Jared. Atila Jared Updike wrote: fromInteger x = [[fromInteger x]] Wouldn't you want the expression [[1,0],[0,2]] + 10 to yield [[11,10],[10,12]] instead of [[11]] ? I guess you would need some complicated machinery so this is one thing you have to ignore to keep your otherwise nifty instance nice and simple. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Simple matrix
Instead of fromInteger x = map repeat (repeat (fromInteger x)) I meant fromInteger x = repeat (repeat (fromInteger x)) but it still doesn't work for multiplication. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie question on iterating over IO list
o To output anything, I need to do 'do'.
If you only have one action, you can omit do, e.g.
main = do { putStrLn Hello, World! }
is identical (after de-sguaring) to
main = putStrLn Hello, World!
Essentially, you are correct; to output anything (i.e. to perform I/O
by side effect) your actions will be inside the I/O monad, typically
inside of a 'do' block.
Jared.
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Re: [Haskell-cafe] ACross
Not to be the bad guy, but perhaps it's a good idea to remind ourselves of our homework policy. This? http://www.haskell.org/hawiki/HomeworkHelp Can I use putString ??? If you mean putStrLn and putStr, then yes. I would first make a function that constructs the string or list of strings (maybe using ++) you need to display, and then call putStr and/or putStrLn the appropriate number of times. Other questions to answer: * Can we safely ignore the case of even numbers?, i.e. cross 2, cross 4, cross 6, etc. * Looking at the output lines, how can we break down or classify them, in terms of numbers of plus signs and areas of spaces? Which lines are similar? etc. Good luck, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Learning C after Haskell
Thanks, Minh. So are things like recursion and memory sharing typically out the window? Recursion works in C, but every function call pushes stack, so recursive depth is limited by RAM (compare to tail call optimization in many functional programming languages where the stack frame is reused if code is written iteratively with an accumulator). Most of the time for performance (and to be idiomatic) in C you will just write for and while loops and modify state in place. Welcom to C. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Separate a string into a list of strings
Funny. I have a module called Useful.hs with some of these same sorts
of functions. (coming from Python where I used .split(',') and
.replace('\r', '') and such a lot):
--
module Useful where
import List ( intersperse, tails )
import Numeric ( readHex )
hex2num :: (Num a) = String - a
hex2num s = let (result, _):_ = readHex s in result
toEnv s = map tuple (split ';' s)
tuple :: String - (String, String)
tuple line = case split '=' line of
a:b:_ - (a,b)
a:_ - (a,)
_ - (,) -- not good, probably won't happen for my typical usage...
split :: Char - String - [String]
split _ = []
split c s = let (l, s') = break (== c) s
in l : case s' of
[] - []
(_:s'') - split c s''
beginsWith [] [] = True
beginsWith _[] = True
beginsWith [] _ = False
beginsWith (a:aa) (b:bb)
| a == b = aa `beginsWith` bb
| otherwise= False
dropping [] [] = []
dropping [] _ = []
dropping x [] = x
dropping s@(a:aa) (b:bb) | a == b= dropping aa bb
| otherwise = s
-- replace all occurrences of 'this' with 'that' in the string 'str'
-- like Python replace
replace __[] = []
replace this that str
| str `beginsWith` this = let after = (str `dropping` this)
in that ++ replace this that after
| otherwise =
let x:xs = str
in x : replace this that xs
eat s = replace s
-- sometimes newlines get out of hand on the end of form POST submissions,
-- so trim all the end newlines and add a single newline
fixEndingNewlines = reverse . ('\n':) . dropWhile (=='\n') . reverse .
filter (/= '\r')
endsWith a b = beginsWith (reverse a) (reverse b)
a `contains` b = any (`beginsWith` b) $ tails a
--
Jared.
On 6/12/06, Neil Mitchell [EMAIL PROTECTED] wrote:
Hi,
I tend to use the module TextUtil (or Util.Text) from Yhc for these
kind of string manipulations:
http://www-users.cs.york.ac.uk/~malcolm/cgi-bin/darcsweb.cgi?r=yhc;a=headblob;f=/src/compiler98/Util/Text.hs
separate = splitList ,
I am currently thinking about making this module into a standalone
library with some other useful functions, if people have any opinions
on this then please let me know.
Thanks
Neil
On 6/12/06, Sara Kenedy [EMAIL PROTECTED] wrote:
Hi all,
I want to write a function to separate a string into a list of strings
separated by commas.
Example:
separate :: String - [String]
separate Haskell, Haskell, and Haskell = [Haskell, Haskell, and
Haskell]
If anyone has some ideas, please share with me. Thanks.
S.
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Re: [Haskell-cafe] Features of Haskell
stumped as to how I'm going to do this. I've got about 15-20 minutes, so I can only discuss the major features. I was always impressed with Autrijus Tang's presentation here: http://www.pugscode.org/euroscon/haskell.xul (view with Firefox or other Gecko-based browser) I think he managed to explain very effectively what made Haskell special, including major features/differences/paradigms, as well as syntax, all at once. I did read the slides as one familiar with Haskell so I can't say how it would come across to one unfamiliar with Haskell (which was his target audience), but maybe his presentation will help give you ideas. Best of luck! Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Features of Haskell
On Sun, Jun 04, 2006 at 05:17:02PM -0700, Jared Updike wrote: stumped as to how I'm going to do this. I've got about 15-20 minutes, so I can only discuss the major features. I was always impressed with Autrijus Tang's presentation here: Audrey I think he managed to explain very effectively what made Haskell ^^ she Yep.. My bad. Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC wish
Sorry, meant to reply all: --- This tool (DrIFT) can derive these instances for you, if you care to make rules for it, for Pretty: http://repetae.net/john/computer/haskell/DrIFT/ Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] develop new Haskell shell?
It would also be wise to look at occam and erlang and see if they have any useful ideas. And, of course, Windows PowerShell. And scsh (Scheme shell, pretty full featured these days): http://www.scsh.net/ Jared. j. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie Instance Of Floating Int Error
It looks like somewhere else in your program (or a type signature somewhere) is trying to force the result of sqrt to be an Int which won't work since square roots are irrational (represented by the computer as a Float or Double). You might try (1) making sure the place where distBetween is used isn't trying to use only Ints or Integers and (2) taking off explicit type signatures and seeing if that works (the compiler can usually get things working for you as long as you don't give it misinformation in type signatures). Also, a more useful type of Point if you are taking distances would be type Point = (Float,Float) instead (or you can leave that out because the function type for distBetween will be inferred to be the right thing, i.e. (Float,Float) is already a valid type without needing to be named). Hope that helps, Jared. -- http://www.updike.org/~jared/ reverse )-: On 4/27/06, Aditya Siram [EMAIL PROTECTED] wrote: Hi all, I just started working with Haskell and am having some difficulties with its type system. Here is function that is supposed to calculate the distance between two coordinates: distBetween (x1,y1) (x2,y2) = sqrt((x2-x1)^2 + (y2-y1)^2) I am trying to explictly give it a type signature. Here is what I have tried and the errors generated by Hugs: type Point = (Int,Int) distBetween :: Point - Point - Float ERROR - Type error in explicitly typed binding *** Term : distBetween *** Type : Point - Point - Int *** Does not match : Point - Point - Float distBetween :: Point - Point - Int Instance of Floating Int required for definition of distBetween Any help is appreciated... Deech ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] RuntimeLoader
I've never used that Runtime Loader package but I have gotten hs-plugins to work: http://www.cse.unsw.edu.au/~dons/hs-plugins/ Hope that helps, Jared. On 4/13/06, Tim Newsham [EMAIL PROTECTED] wrote: Hi, I'm about to start playing with HWS-WP (web server + plugins). It relies on RuntimeLoader: http://www.algorithm.com.au/wiki/hacking/haskell.ghc_runtime_loading I grabbed the example and built it (only one minor tweak to imports to get it to build) but it doesnt quite work: $ ./src/TextFilter ./plugins/Lower.o README TextFilter: ./plugins/Lower.o: unknown symbol `__stginit_Char_' TextFilter: user error (resolveFunctions failed?False) There were also some warnings during building: Compiling RuntimeLoader( ../runtime_loader/RuntimeLoader.hs, ./RuntimeLoader .o ) /tmp/ghc11951.hc: In function `s2Pj_ret': /tmp/ghc11951.hc:170: warning: implicit declaration of function `unloadObj' /tmp/ghc11951.hc: In function `s2JU_entry': [...] I assume this is because it is mucking with some ghc internals? Is anyone familiar with this package? Is there a more up-to-date version or alternative? Tim Newsham http://www.lava.net/~newsham/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] web servers
I don't know if there's anything newer, but you could check out: http://happs.org/HAppS/README.html http://www.informatik.uni-freiburg.de/~thiemann/WASH/ Hope that helps, Jared. On 4/8/06, Tim Newsham [EMAIL PROTECTED] wrote: Hi Everyone, I'm new to the list, been on irc a bit. I'm still learning haskell. Wanted to say Hi before getting in to things... I'm interested in real-world programs in haskell, especially ones where security and formal methods are important. I'm looking at web servers right now. I found a copy of Simon Marlow's HWS on haskell.org's cvs server. I know there's a newer plugin version, but I cant find a working link to the actual code. I've been able to get the code to compile after a while, but it still has some warnings of deprecated features which I havent been able to get rid of (if anyone's interested in helping out, let me know). Anyway, I configured it an ran it and it works, although I have noticed two security flaws in it which need fixing. Is it possible there is a newer version with these flaws fixed? Besides HWS, what other web servers exist? Does anyone actually use a haskell based web server in practice? Which web server is considered the most mature? stable? fastest? I'm trying to decided if I should sink some time into HWS or if I should use another server. Tim Newsham http://www.lava.net/~newsham/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Justification for Ord inheriting from Eq?
given an Ord instance (for a type T) a corresponding Eq instance can be given by: instance Eq T where a == b = compare a b == EQ where did this second -^ == come from? (I guess if if Ordering derives Eq :-) I think you meant instance (Ord T) = Eq T where a == b = case compare a b of EQ - True _ - False Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] What's up with this Haskell runtime error message:
Thanks so much for your help. I should have made clear that I was aware that the definitions were mutually dependent. What I was hoping was that Haskell could solve this for me without my having to resort to effectively finessing any sequencing considerations. Haskell is a functional language. The program you are trying to solve sounds like a logic problem if I understand it correctly. There is a functional logic programming language called Curry [1] that has similar syntax to Haskell, but a different evaluation approach. (Note: I don't know anything about Curry other than what I read on the front page of their website, and the fact that someone wrote a Sudoku solver by writing the constraints and having the compiler generate a program that solves the puzzle.) Perhaps I am really asking it to do too much. What you want is a program that looks for a set of values that satisfy a certain set of mathematical relations (you mentioned scientific computing). As I understand it, this is where logic programming shines. (If you can turn this into a system of equations, Mathematica might be able to solve it, btw.) This I thought might be reasonable since one is supposed to be achieving a sequence-less style of programming. I never really heard Haskell described this way. I've heard Haskell described as a declarative programming language, where you shouldn't worry about the order of execution of your functions, but I never thought it meant anything about complete sequence-less-ness; it seems very rooted in deterministic evaluation. But this would seem to be a counter example where I will be essentially forced to implement a sequential processing semantic in a language environment which ostensibly would deny me such (for my own good I understand). In fact, Haskell is big on sequencing. One of the key features of Haskell is the monad [2]; you might call it sequencing done right. I'm not sure how monads would help you (if you can express your code imperatively you are good to go, but it sounds like you want to keep things declarative). Thoughts? Someone who knows about logic programming might point you to good resources about this perspective, if it applies (other than Curry [1]), which looks pretty fun. Hope that helps, Jared. [1] http://www.informatik.uni-kiel.de/~curry/ [2] http://www.nomaware.com/monads/html/ -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code Review: Sudoku solver
On 4/3/06, Donald Bruce Stewart [EMAIL PROTECTED] wrote: It would also be nice to see some example sudoku solvers posted on an `Idioms' page on haskell.org: http://www.haskell.org/haskellwiki/Category:Idioms someone could just create a new page 'Sudoku' and add the phrase [Category:Idioms]] to the text, and it will be indexed. Done. Lives at http://www.haskell.org/haskellwiki/Sudoku Seeing 4 or 5 solutions would be a useful tutorial, I'd imagine. it seems that sudoku solver may be a good candidate for nofib suite / language comparison shootout Anyone with killer solvers (Chris?) can add them to the wiki. Maybe the fastest can be used in a new Shootout benchmark. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code Review: Sudoku solver
Chris wrote: You need more than 5 examples. The truly evil puzzles are rarer than that. Go get the set of minimal puzzles and see how far your logic takes you. Chris elucidated some of my questions before I finished writing my email... Claus wrote: (*) actually, that was a bit disappointing!-( How much harder is the problem of generating (hard/medium/easy) (solvable) Sudoku puzzles? Are all puzzles solvable (that don't break the rules at any point)? I imagine a simple way is to start with a correctly saturated grid of numbers and then start randomly shooting holes in it and testing if it is still solvable (either unambiguously or ambiguously) with your Sudoku solver? A rough mesaure of the difficulty of the unsolved puzzle could be how long the solver took to solve it (number of steps) (and the number of possible solutions)? Are puzzles with multiple solutions usually considered harder or easier? Are these considered proper puzzles? Is this a more interesting problem to try to solve (generating) rather than solving puzzles? I haven't investigated it much but I thought about it when I was writing YASS (Yet Another Sudoku Solver) of my own. What makes a Sudoku puzzle fiendish? Just the amount of missing information, the amount of lookahed required? Jared. P.S. Another interesting problem could be trying other number arrangements besides 9x9, e.g. hexadecimal puzzles... I wrote my solver to handle these but I never saw other than 9x9 puzzles to try it on (hence the idea of generating puzzles)... Is that because most people want puzzles to solve by hand instead of computer? -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PPM image manipulation
having some trouble trying to be able to manipulate PPM images. I want to be able to desaturate and also double the scale of them. im a first time user of haskell so am not very familiar with it. any info would be great! thanks! Nothing wrong with asking for help, but before you do, please read: http://www.haskell.org/hawiki/HomeworkHelp After you read that and follow its advice, we would love to help with *specific* questions (code help or algorithms, for example). I have a few questions for you: Do you understand how to do these image manipulations, for example, in another programming language? Are you confused about how to do this in Haskell? Or both? If these manipulations are difficult, try something simple, like inverting the image or keeping only the red channel (zero out blue and green), anything to make sure you have a handle on the code. Thanks, Jared. P.S. After googling around for haskell image manipulation (in the hopes of finding some Haskell image lib like VIPS [1] or the Python Imaging Library [2]), I found the assignment spoken of http://cs.anu.edu.au/Student/comp1100/assts/asst1/ just so everyone knows. BTW, does Haskell have an imaging library that people usually turn to? (Or should I add that to my list of cool projects that I need to get around to ...) [1] http://www.vips.ecs.soton.ac.uk/ [2] http://www.pythonware.com/products/pil/ -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Distributing monadic(?) functions across dyadic functions
Is there a common way (standard libs, higher order) to express the lambda part below? It's not particulary complicated but I think it is not higher-order enough unionBy (\x y - fst x == fst y) listOfPairs1 listOfPairs2 Something like distribute fst (==) where distribute f op x y = f x `op` f y would leave unionBy (distribute fst (==)) listOfPairs1 listOfPairs2 I imagine something involving Arrows and/or zip/curry/uncurry but I just can't see it. Is this a case of trying to make something more complicated than it is? Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] List of instantiated types
My understanding is that type classes in Haskell are meant to be
open, so that any code that uses your type class will work with any
new instances of that type class. This inherent open endedness causes
a problem if you are trying to enumerate all instances because at any
time someone can create a new instance of your class in their code.
There is a ticket for Haskell' talking about Closed Classes but I'm
not sure it would be adopted anytime soon (and I'm pretty sure it's
not implemented in GHC):
http://hackage.haskell.org/trac/haskell-prime/wiki/ClosedClasses
What you're trying to do *may* be possible but it would require some
way of having the runtime query the compiler/linker for information
about all modules being linked against.
This kind of hacking may require hs-plugins, Template Haskell, or the
GHC API (i.e. some kind of metaprogramming).
What I mean is, I'm not sure how to make it so you can gather all
information about your type class in one central place; I think for
type classes the information flows in the other direction. There might
still be a totally different way to accomplish this but you'll have to
wait for a guru to answer that...
Hope that helps,
Jared.
On 3/30/06, Mirko Rahn [EMAIL PROTECTED] wrote:
Hello,
please suppose the following setting: (see [1] too)
{-# OPTIONS_GHC -fglasgow-exts #-}
module C where
class C a where name :: a - String ; pre :: a - a
data Cs = forall a . (C a) = Cs a
instance C Cs where name (Cs a) = name a ; pre (Cs a) = Cs (pre a)
mkCs :: C a = a - Cs
mkCs = Cs
instance C Int where name = show ; pre = \ _ - 0
instance C Char where name = return ; pre = \ _ - 'A'
all_Cs = [ mkCs (undefined :: Int), mkCs (undefined :: Char) ]
Note that despite I served undefined values only I can type
*C map (name . pre) all_Cs
[0,A]
to extract some information. But, when several instances spreads over
some modules, writing down 'all_Cs' is an error-prone task, in
particular when using some third party modules.
So my question is: Is it possible to construct 'all_Cs' automatically?
I think such a list cannot be constructed at compile-time, but at link-
and run-time a complete list of instantiated types should be available.
But is this list accessible somehow? Is there a possibility to write
foreach type t that is an instance of C:
return (mkCs (undefined :: t))
What is the general problem?
Thanks, MR
[1] http://www.haskell.org/pipermail/haskell-cafe/2006-March/014947.html
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Re: [Haskell-cafe] Positive integers
Fortunately there are already List functions like genericLength and genericTake, which can handle such a number type. Shouldn't be Peano numbers part of the standard libraries? Natural numbers are being discussed as a possible part of the new Haskell' standard. http://hackage.haskell.org/trac/haskell-prime/ticket/79 Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Positive integers
An additive torsor is? Surprisingly, there is a page on MathWorld about Torsors but it is empty. Google turned up the following page with a good explanation. http://math.ucr.edu/home/baez/torsors.html I'd maintain that the difference between two lengths is an entirely different quantity from the length of a list. (Maybe this is a good example of what the term torsor captures.) Thanks to Aaron for expanding our vocabulary. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code Review: Sudoku solver
On 3/22/06, David F. Place [EMAIL PROTECTED] wrote: Hi All, I really appreciate all the help I received when I asked you to critique my PrefixMap module a few weeks ago. I think I am making good progress in correcting the lisp in my Haskell programming. I'll be very grateful to anyone who can take a glance at the attached short program and say if any unidiomatic usages pop out Try cellIndex r c = 3*(r `div` 3) + c `div` 3 It's much much shorter and should produce the same results. It solves sudoku puzzles. (What pleasure do people get by doing these in their heads?!?) They are probably asking the same question: why take hours to write a program to do it when with my mad sudoku solving skills I can solve it in X seconds? My roommate is like this. Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: dynamic arrays
(Moved to haskell-cafe) JU General question to the list: JU (Q) Are there any data structures in Haskell similar to C++/STL JU vectors or C# generic Lists (i.e. strongly typed ArrayLists, e.g. JU Listint)? These data structures grow automatically as you add JU elements to them (but in large chunks, not one node at a time). This JU data structure (if it exists in Haskell) would run inside a monad (ST JU and/or IO) and it would automaticly resize when needed, but would be JU more or less like a mutable array except you can add new elements to JU the end of it without reallocating an entire array of n+1 elements... i tried to implement this today :) but there is one problem: if i have (l,u) - array bounds of type Ix, and i - offending index of the same type, how can i compute new bounds of array so that it will grow in large chunks? there is no such computation operations for Ix type and that is logical - if this array is really a matrix then it's hard to use the same rules of extending it as for vectors Hmmm, that is a problem, especially as you said, for enum types that are bounded above. I guess you can't make it grow more than the min and max. For the most part, this dynamic array would only be useful for arrays with indices isomorphic to the natural numbers. such computation as (u-l)*2+l is great for integral indexes, but not for general case. now i plan to use this strategy for all enum types and just grow to minimal and maximal indexes actually used for other index types Perhaps the function to build these DynamicArrays could take a Maybe parameter telling the maximum possible range (for bounded enums) or Nothing if the array is allowed to grow indefinitely. Or an Either parameter where Left (a,a) tells the max range and Right (a,a) - (a,a) which tells how the range should grow on a resize. Or just the range resize function :: (a,a) - (a,a) telling how to grow on a resize, i.e. for enums function = id. Something like that. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Learning from scratch
For GHC try adding the line import Data.Char or import Char at the top of your Haskell program. Or in ghci, try Char.chr instead of chr, etc. Or try ghci filename.hs where filename.hs is a text file with the line import Char at the top. Now 'chr' should appear in scope. The hierarchical libraries are listed here: http://haskell.org/ghc/docs/latest/html/libraries/ (scroll down to see all the modules listed) You can search for functions here, e.g.: http://haskell.org/hoogle/?q=chr Good luck, Jared. On 3/15/06, Xavier Elizalde [EMAIL PROTECTED] wrote: I'm just starting to learn Haskell from scratch and I've just hit a snag. The book Haskell: The Craft of Functional Programming, Second Edition uses some examples that call functions from Prelude.hs. But for some reason, two installations of Haskell that I have on my computer don't have the functions available. I have the OS X version of Hugs (http://www.haskell.org/soe/software.htm) for the book The Haskell School of Expression installed, as well as the latest version of the Glasgow Haskell Compiler. Both of them get errors with the functions such as ord and chr mentioned at the beginning of the first book mentioned. Where can I get Prelude.hs and the other files it needs, and what do I do with them? I'm going to move on to the School of Expression book after the Craft of Functional Programming book, which is why I have the SOE version of hugs installed. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] Trying to get a Composite design pattern to work
(Moved to haskell-cafe) Actually, I'm trying to avoid library functions, so I can learn the language and the functional way of thinking. How would one implement the concatMap function? The Haskell 98 report gives possible implementations of standard functions: http://haskell.org/onlinereport/standard-prelude.html e.g. foldr:: (a - b - b) - b - [a] - b foldr f z [] = z foldr f z (x:xs) = f x (foldr f z xs) map :: (a - b) - [a] - [b] map f [] = [] map f (x:xs) = f x : map f xs concat :: [[a]] - [a] concat xss = foldr (++) [] xss concatMap :: (a - [b]) - [a] - [b] concatMap f = concat . map f etc. The book Haskell School of Expression (by Paul Hudak) goes over using recursion as a control structure and then shows you how to replace your simple recursion patterns with library functions once you start to see these general patterns. As you start to understand the functional style of iterating over lists, you should begin to see when to use the library functions, and how it will save you time and be more simple and clear than using recursion directly for every function. If you want a place to start, I would challenge you to expand the concatMap definition above with the definitions of concat and map, and then plug in the definition of foldr and see if you can make your own concatMap function. Maybe that will help you understand things better. Hope that helps, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] | vs. $ (was: request for code review)
Dude, that was a friggin' awesome email! I'm trying to figure out how
I can just copy it wholesale into the article ;)
Use what you need. Share and share alike.
I've been struggling
with Haskell for long enough that my knowledge is now snowballing
downhill.
I think I experienced that too. I like how Haskell is about the
concepts (even things you didn't know you were already doing
implicitly) and the language is just a very transparent vehicle for
manipulating them. Haskell has really taught me a lot and helped me
think a lot clearer---but now I think in Haskell! The danger is that
since I've taken the red Haskell pill I have a hard time looking at
the imperative world the same way. I have to resist trying to cram all
these elegant approaches into a system that can't support them and
instead program like a normal person. (The good news is that many
languages are slowly soaking up features, e.g. C# delegates are
higher-order functions and anonymous delegates are lambdas, C# 3.0
will have some kind of type inference, etc. but these features are
many decades old.)
Everything you said made sense 100%.
To add a few more comments to this: in Haskell you don't overload the
semicolon, instead you overload = (bind) and create a new
typeclass with this function (as well as a function called return,
where these two functions obey certain laws that keep things kosher,
i.e. return is the identity, = is associative, and they interact
as you would expect). It just so happens that the semicolons (or
newlines) in do blocks get converted into =s and lambdas to scope
your variables over the rest of your actions.
The reason monads are cool and magical is that now that we've made
this sequencing explicit in the type, we can swap out the machinery
(what type of implicit state we're passing around or even the =
function itself) and change a minimal amount of code, i.e. nothing...
except adding code to use the new functionality (if all goes well). We
can now get continuation passing, or true mutable variables (e.g.
IORef), or a simple sort of non-determinism (e.g. List as a monad), or
failure (Maybe) or exception handling, or any number of behaviors (or
combinations) by changing the monad.
BTW the original discussion was about composing functions and I gotta
say since C programmers don't really think in terms of f . g x = f (g
x) anyways, and since writing code in the order it executes is
natural (think Python str.replace('\r', '').split('\n') ), I think
the idea of explaining | as a pipe is pretty cool. There might be a
little too much overhead in explaining things if you drop the M-bomb
(monads), but if you can make and keep monads clear and simple and use
them there, you will have accomplished a great feat (and analogies
like Unix pipes are a good thing). I'm curious to see how this
evolves.
Good luck.
Jared.
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Re: [Haskell-cafe] | vs. $ (was: request for code review)
I suspect you guys are right. I had always thought of states as being isomorphic to integers (i.e. you can be in state 0, state 1, ... state n), not as contexts (you have this input, that output, and this token stack), am I wrong? You're thinking of a state machine, I think, which is not quite what a state monad would do here. (I have nightmares of writing a state-machine parser in assembly like I did in an EE class once... ouch). I suspect I need to spend more time trying to understand the state monad. I must admit that I baulked the last time I tried to squeeze it into my head. I'll just need to try again ;) Here's the way I like to think about state in imperative programs---it's hard because it's not something you can get far away from enough to see, usually. In imperative programs, the value of a variable 'a' at one point is not always the value of the variable 'a' at another point later in the code. In some sense, each statement that gets executed is passed the entire state of the machine (the world) implicitly, and then when the statement ends, it passes the state of the world on to the next statement. If you want to access the value of the variable 'a', then 'a' gets looked up in the environment/state. In C/C++/Java/C#/Python/Perl, etc. this is done for you automatically and efficiently. It's just the way the machine works. But you don't have the choice to change this or, as someone put it, overload the semicolon. In Haskell none of this variable-mutating, state-passing **can** occur, so it gets created from scratch, and voila, we have the State Monad. It makes it sound like a lot more work than it should be just to do something that comes for free in most other languages, but in these languages, you can't overload the semicolon! And if you could, who knows what could go wrong at runtime (imagine Perl with semicolon overloading... I bet some day they will do this just because they can...). In Haskell, everything is watched over by the type system, so the parts of your program that explicitly need to munge state are isolated with the some type tag, e.g. ParseContext, while the rest of your program is normal and pure and functional. The problem with monads is not that they are advanced but that they are so painfully and subtly abstract (I was going to say subtly simple but maybe they aren't for most working non-Haskell programmers...). (It just so happens that you **can** do amazing, convenient, efficient, magic and otherwise advanced things with them, especially with the libraries.) Another problem is that everyone has different ways of explaining them or trying to define what they are (a way of sequencing computation? or a type constructor? or a type class?). Of course, they are all those things, which makes it even more confusing. At a certain point, though, I think they just subconciously click and boom, now you get it. Anyway, if your goal is to get people to understand Haskell, then see if you can use monads to simplify things. If your goal is to do a straight translation of the C code, don't worry about monads. My 2c, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code reviewrequest)
Layout only applies when something is less indented than previous lines, I believe... e.g. do c - getContents filename putStrLn blah or do x - getContents filename putStrLn ok works fine but do c - blahAction putStrLn blah obviously won't work Jared. On 3/2/06, Brian Hulley [EMAIL PROTECTED] wrote: Brian Hulley wrote: [snip] So any solutions welcome :-) Thank to everyone who replied to my queries about this whole layout issue. One other thing I've been wanting to ask (not to change! :-)) for a while is: how is the following acceptable according to the rules in the Haskell98 report where where is one of the lexemes, which when followed by a line more indented than the line the layout-starting-lexeme is on, should start an implicit block: module M where data T = .-- not indented! According to my understanding of the layout algorithm, the above code would have to be written: module M where data T = Can anyone shed some light on what the formal rule is that allows the first (and very useful) way of laying out code to be ok? Thanks, Brian. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Layout rule (was Re: PrefixMap: code review request)
BH Why? Surely typing one tab is better than having to hit the spacebar 4 (or 8) BH times? PC Not when it prevents me from ever exhibiting the slightest shred of style PC in my code. I use that control for readability purposes in my code. [snip] BH I'm really puzled here. I've been using tabs to indent my C++ code for at BH least 10 years and don't see the problem. At least two reasons: 1. C++ doesn't care about any whitespace (except to separate tokens). Haskell cares about leading whitespace (which it is clear you are thinking a lot about...) but 2. as Philippa mentioned, Haskell programmers care a ton about inter-line, inter-word layout/alignment, for example, lining up = signs and arguments to functions in pattern matches, etc. C++ does not invite this style of declarative programming so it is not surprising that it wasn't an issue: aside from the indentation, I rarely type fancy whitespace inside a giving line of C++ code to align elements with those on a preceding line. In Haskell, this unofficial layout style doesn't affect the machine-parsing of the code, but rather the human-parsing of the code. (In fact, it's one of my favorite things about Haskell.) If you want to see what can be accomplished with variable width fonts and complex layouts (not just beginning of lines but rather inter-line, inter-word alignment) you should checkout lhs2TeX. They accomplish all their magic with spaces. BH The only problem would be if BH someone mixed tabs with spaces. Since it has to be either tabs only or BH spaces only I'd choose tabs only to save keystrokes. BTW, tab doesn't type the tab character (at least in emacs and I think vim) but instead moves the left edge of the current line by adding or deleted spaces (or trying to ident the right amount). This usually means you don't have to type 4 or 8 spaces. (And anyway, I would just hold the key down if I had to type more than one spacebar, etc.) [snip] For example on Windows Trebuchet MS is a very nice font, also Verdana, both of which are not monospaced. But yes I agree it's not a major issue and I just see the option of being able to use them as a nice side-effect. Very few programmers I know would go to variable width fonts just to use some Microsoft font to edit code... (BTW I like Trebuchet and Verdana too.) To each his/her own! Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] rounding errors with real numbers.
Well, if you are relying on exact results from floating point arithmetic you're in trouble no matter what you do. As long as you don't do anything irrational (exp, sin, sqrt, etc.), you should be able to get away with using Rational. Number constants with decimals are not automatically constructors for floating point numbers in Haskell; they are exact (fromRational) until you make them Doubles or some other floating point value. If you have to use Doubles for other reasons (performance/memory, interfacing with other code, etc.) this won't help you... Just my 2c. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monads (was how to write an interactive program ? gui library to use ?)
(Note, moved to haskell-cafe.) Essentially, the answer is yes, the state needs to be passed around (neglecting hackery to simulate global variables that is better avoided). However, this can be made convenient by using a monad. BTW, Minh, If you don't know what monads are, then read this. Monads are an indispensable part of programming in Haskell: http://www.nomaware.com/monads/html/ http://haskell.org/hawiki/Monad Monads are good. Monads are your friend. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Infinite loop?
Yep. change one line to: entry - if isdir name /= . name /= .. and it does in fact work. Jared. On 2/17/06, Jon Fairbairn [EMAIL PROTECTED] wrote: On 2006-02-17 at 20:12GMT rgo wrote: Hi all, my program probably goes into infinite loop... But i cannot understand where and why. getDirectoryContents will include . and .., so if you follow those, you're bound to loop. -- Jón Fairbairn Jon.Fairbairn at cl.cam.ac.uk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems instancing a class
type introduce a type synonym, and Haskell98 forbids these in instances, so GHC complains. GHC also lifts this restriction when invoked with -fglasgow-exts . http://www.haskell.org/ghc/docs/latest/html/users_guide/type-extensions.html#type-synonyms Flexible Instances will probably be added to HaskellPrime: http://hackage.haskell.org/trac/haskell-prime/wiki/FlexibleInstances This page: http://cvs.haskell.org/Hugs/pages/users_guide/class-extensions.html#FLEXIBLE-INSTANCES says that ultimately you would turn the type language pretty much into Prolog (which would allow more expressive power---and less inconvenience as we both would like--but make general type checking undecidable). Instead they do a more conservative extension with a fixed depth of constraints it will check so the compiler will terminate. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell as scripting language?
For scenario (a) you can use hs-plugins and ghc http://www.cse.unsw.edu.au/~dons/hs-plugins/ With hs-plugins you can get an eval command, or you can dynamically load Haskell modules (from source or pre-compiled .o files). GHC (= 6.5) has an API that you can access from Haskell programs: http://www.haskell.org/haskellwiki/GHC/As_a_library I was wondering if the new GHC API gives you everything hs-plugins does? If not will it ultimately do what hs-plugins does and replace it, in the future? Jared. On 2/15/06, Marc Weber [EMAIL PROTECTED] wrote: Is there a way to use haskell as scripting language in a) your own project? b) other projects such as vim (beeing written in C)? At the moment I'm interested, I don't have any real project.. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Matching constructors
Or inline as findIndices (\x - case x of Tootie _ - True; _ - False) listOfPasAndTooties There was a recent thread about wanting a more succint way to write this (unary pattern matching): http://thread.gmane.org/gmane.comp.lang.haskell.cafe/11109 If John got his wish, then you could write something like findIndices (@ Tootie _) listOfPasAndTooties Maybe this feature will appear in a future Haskell standard? though I don't see anything on the Haskell' wiki about this... Cheers Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell reference card ?
On the new wiki, there is a keyword page as well (probably copied from the old wiki): http://haskell.org/haskellwiki/Keywords I agree that it would be nice to have a reference card page much like yours, Neil. So I made it on the wiki: http://www.haskell.org/haskellwiki/Reference_card By the way, what is the current plan for the old wiki? Should new improvements be made to the new wiki (http://haskell.org/haskellwiki/...) instead of the old one (http://haskell.org/hawiki/...) ? Is the old wiki supposed to get gradually merged into the new wiki/website? I understand it would be a bad idea to take it down (so it will probably be there for a long time) but is it supposed to be deprecated any time soon? Jared. On 2/7/06, Neil Mitchell [EMAIL PROTECTED] wrote: is there somewhre Haskell reference card ? I attempted to start one quite a while ago: http://www.nmitchell.co.uk/code/haskell.htm But its not complete, and it was quite a while ago, so it may be wrong (but on the other hand, it may be useful) I also attempted to start a keyword list on the old haskell wiki http://www.haskell.org/hawiki/Keywords Perhaps there should be a wiki page for this? In which case, people are welcome to copy either of those above pages. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] main features of functional programming paradigm
I would like to ask about what are tha main features of functional programming? If you are new to functional programming, read this http://haskell.org/haskellwiki/Introduction What kind of software can i develop with this methodology? I'm not sure what you mean by your question as it is very general. (If you are refering to the methodology in the FAD paper at http://www.cs.kent.ac.uk/pubs/2001/1152/ , I haven't read it so I can't help you there.) With Haskell, you can develop pretty much any kind of software, as any other programming language. See http://haskell.org/haskellwiki/Applications (If you want to develop a compiler or interpreter, you are in luck as functional programming languages are very good for developing this kind of software.) What kind of software are you intending to develop? Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is $ right associative instead of leftassociative?
[a,b,c ; tail] === a :: b :: c :: tail -- where :: How is [a,b,c ; tail] simpler, clearer or less typing than a:b:c:tail ? I think that the commas and semicolons are easy to confuse. While we're talking about the aesthetics of :: and :, I like how a line with a type annotation stands out strongly with ::, e.g. map :: (a - b) - [a] - [b] Compare this to map : (a - b) - [a] - [b] where the identifier looks more connected to the type. You will notice this is different than ML anyway because in Haskell you can separate the type annotation and the declaration. If you are designing your own langauge, you will of course have your own aesthetics and reasons for doing it your way. As for me, I started to design (in my head) the perfect language (for me), but the more I learned and used Haskell, the more I realized how carefully designed it was and how it was better for me to use my efforts to learn from Haskell (especially conceptually, since the syntax is so transparent and the ideas are so amazing) than to try to insert clever ideas to satisfy my own whims. Sure, there are always little things to nitpick, but on the whole, can you think of more succinct language with more power? (and less parentheses!) Plus, what other languages let you more easily add (infix) operators, etc. and change things to fit your whim, anyway (and still be strongly type!). Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell code for this example of flow control
I would use recrusion and the Prelude function until: until (=1) (/2) 1000 Cheers, Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can I use Haskell for web programming
For haskell-fastcgi, my configure fails with cannot satisfy dependency cgi-any Google does not turn up any useful results for this. Which package will fix this dependency? I thought I just installed fastcgi from source but I'm not sure where it gets looked for by haskell-fastcgi... Thanks Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Can I use Haskell for web programming
Interesting. It's hosted on Haskell site. Do you think I would be able to do what you have done in a professional hosting service computer? If you don't need dynamic web pages, you could develop the pages on your own machine, generate HTML, etc. and then upload those to the server of your choice. It may also be possible to deploy just the compiled binaries (for the appropriate platform, i.e. BSD, Linux, whatever the host uses) if you need CGI functionality and the hosting service gives you the OK. I just run Ubuntu Linux (so I can put whatever packages I need on there) on a machine connected to a DSL modem and use dynamic DNS to keep the name pointed at my computer, but I don't have high bandwidth needs. I'm finding Haskell to be a really nice language for generating webpages, much better than doing things by hand or even using Python, for example. Jared. -- http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] formal methods functional programming
I can't think of any Haskell papers about ``formal methods'' in software engineering, but many papers and books talk about proving program correctness, which is difficult in traditional, imperative languages (which is why it is probably not stressed as much as //testing// is in formal software methods). Paul Hudak, in the textbook, The Haskell School of Expression (http://www.amazon.com/gp/product/0521644089/104-7074974-5852762?v=glancen=283155) writes a lot about proving program correctness (especially induction on recursive algorithms) for Haskell and purely functional programs, reasoning mathematically. If you want to do strenuous testing, you can use QuickCheck: Automatic Specification-Based Testing: http://www.cs.chalmers.se/~rjmh/QuickCheck/ A professor I had at Caltech researches formal methods in constructing reliable software systems, specifically using robust programming language and compiler technology (in this case OCaml). http://mojave.caltech.edu/ Jared. On 1/14/06, Abigail [EMAIL PROTECTED] wrote: Hi, I have been searching papers about tha raltionship between formal methods in software engineering and functinal programmming, but i haven't found enough information. can u hel me?. Thanks Abigail. __ Correo Yahoo! Espacio para todos tus mensajes, antivirus y antispam ¡gratis! Regístrate ya - http://correo.espanol.yahoo.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Splitting a string into chunks
That works except it loses single newline characters.
let s = 1234\n5678\n\nabcdefghijklmnopq\n\n,,.,.,.
Prelude blocks s
[12345678,abcdefghijklmnopq,,,.,.,.]
Jared.
On 1/13/06, Sebastian Sylvan [EMAIL PROTECTED] wrote:
On 1/13/06, Sebastian Sylvan [EMAIL PROTECTED] wrote:
On 1/13/06, Adam Turoff [EMAIL PROTECTED] wrote:
Hi,
I'm trying to split a string into a list of substrings, where substrings
are delimited by blank lines.
This feels like it *should* be a primitive operation, but I can't seem
to find one that works. It's neither a fold nor a partition, since each
chunk is separated by a 2-character sequence. It's also not a grouping
operation, since ghc's Data.List.groupBy examines the first element in a
sequence with each candidate member of the same sequence, as
demonstrated by:
Prelude :module + Data.List
Prelude Data.List let t = asdfjkl;
Prelude Data.List groupBy (\a _ - a == 's') t
[a,sdfjkl;]
As a result, I've wound up with this:
-- Convert a file into blocks separated by blank lines (two
-- consecutive \n characters.) NB: Requires UNIX linefeeds
blocks :: String - [String]
blocks s = f s
where
f [] = []
f s [] = [s]
f s ('\n':'\n':rest) = (s:f rest)
f s (a:rest) = f (s ++ [a]) rest
Which somehow feels ugly. This feels like it should be a fold, a group
or something, where the test is something like:
(\a b - (a /= '\n') (b /= '\n'))
Off the top of my head:
blocks = map concat . groupBy (const null) . lines
The lines function splits it into lines, the groupBy will group the
list into lists of lists and split when the sedond of two adjacent
elements is null (which is what an empty line passed to lines will
give you) and then a concat on each of the elements of this list will
undo the redundant lines-splitting that lines performed...
Sorry, I got the meaning of groupBy mixed up, it should be
blocks = map concat . groupBy (const (not . null)) . lines
/S
--
Sebastian Sylvan
+46(0)736-818655
UIN: 44640862
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Re: [Haskell-cafe] What does the Haskell type system do with show (1+2)?
http://www.haskell.org/onlinereport/decls.html#default-decls http://www.haskell.org/tutorial/numbers.html#sect10.4 On 1/12/06, [EMAIL PROTECTED] [EMAIL PROTECTED] wrote: What does the Haskell type system do with expressions such as these . . . ? show 1 show (1+2) The type of the subexpressions 1 and 1+2 are ambiguous since they have type (Num a) = a. I'm under the assumption before 1+2 is evaluated, the 1 and 2 must be coerced into a concrete type such as Int, Integer, Double, etc, and before show 1 is evaluated, the 1 must be coerced into a concrete type. Is my assumption correct? If so, how does Haskell know into which type to coerce the subexpressions? If I try to write a new function, my_show, which converts an expression into a string representation that includes type information, I run into errors with expressions like show 1 and show (1+2) because of the type ambiguity. class (Show a) = My_show a where my_show :: a - String instance My_show Int where my_show a = show a ++ :: Int instance My_show Integer where my_show a = show a ++ :: Integer I can avoid the errors if I change it to my_show (1::Int) or my_show ((1+2)::Int). I'm wondering what the difference is between, my_show and Haskell's built-in show that causes my_show to produce an error message when it is used with ambiguous types, but Haskell's show works okay with ambiguous types. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Help compiling School of Expression graphics library?
Someone else had this problem, I think. http://www.mail-archive.com/haskell-cafe@haskell.org/msg11358.html Jared. On 1/11/06, Rakesh Malik [EMAIL PROTECTED] wrote: I'm trying to build the GraphicsLib code in Linux, Fedora. I have the March '05 version of Hugs installed (and ghc, but that doesn't seem to be relevant to this). The first bit of puzzlement comes from the error messages I'm getting: ffihugs +G +LX_stub_ffi.c X.hs Warning: unknown toggle `G'; ignoring. Warning: unknown toggle `L'; ignoring. runhugs: Unable to initialise Hugs (Unrecognised option) Hugs is on my path ($HOME/hugs/bin), and I edited the Makefile to point the hugs_install home directory to $HOME/hugs. X_dir is correct, it has lib/libX11.a and include/X11/X.h. My gc version is: gcc (GCC) 4.0.0 20050519 (Red Hat 4.0.0-8) (I don't know whether that's relevant, but just in case.) Thanks for any help you can provide! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mixing IO and STM
Also, if you are trying to display a line that looks like insert 5 or consume 6 then consider using putStrLn (insert ++ show r) putStrLn (consume ++ show r) instead of print (insert ++ show r) print (consume ++ show r) to avoid printing out the extra quotation marks. The function print is defined in the prelude as print :: Show a = a - IO () print x= putStrLn (show x) also, you could do: putStrLn $ insert ++ show r because the $ infix operator is just a tightly binding function application... you can think of it as a sort of left parenthesis that automatically adds a right parenthesis at the end of your expression. Jared. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Haskell Speed
Back to where this came from, my view is that this is an education issue - tutorials tend to focus on lazy, functional techniques, and not on efficiency. But the material is available, so people *can* learn. It just needs some effort (but possibly more than it should...) Can anyone suggest some good tutorials, papers, or books to read for learning how to reason about laziness, specifically, time and space complexity? I seem to remember that Richard Bird's Introduction to Functional Programming book has a chapter or so on this subject, but what other material would anyone recommend for trying to understand how to write efficient, lazy algorithms? Maybe in the spirit of updating Wikis and such, we can collect this sort of material together... Jared. -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Tutorial uploaded
SKC This entire discussion is about 'breaking a cyclic graph of conceptual SKC dependencies'. Unfortunately, I don't think it can be done well in short SKC amount of time. I bet if we sat down and listed all the concepts required to write idiomatic Haskell (even idiomatic Haskell 98 (whatever this means)), to write programs that do the things that we all have done in other languages (you know what I'm talking about here, but of course this is up for debate too), we would see that it was not a linear structure but a cyclic graph or at best a tree of concepts: we need to understand higher order functions, polymorphic higher order types for monads, monads to understand I/O really well (or to understand WHY I/O in a purely functional language is the way it is), typeclasses, laziness, etc. etc. In a lot of situations, pedagogy is hard to 'linearize'. Why would it be any different in programming? especially in Haskell? A lot of learning Haskell is just helping reinforce this strong, but sometimes subtle base of knowledge required to really start to get Haskell. [1] HT Btw. Simon Thompson states in his book, that he found it didactically HT infelicitous to introduce recursion before higher order functions because HT that let beginners stick to case discriminations and recursive programming HT instead of taking advantage of functions like 'map', 'iterate', 'fold' HT etc. I can confirm this experience and I think that it is similar to IO HT vs. non-IO. It very well may be didactically infelicitous [2]. (I wish there were some program we can just run on a course syllabus and find out that something is felicitous): conceptsInHaskell :: [haskellConcept] conceptsInHaskell = [...] -- abstract main = print $ sort conceptsInHaskell .. error: haskellConcept not a member of class Ord. Maybe we'll (collectively) get better and better at this. I think we are. Hopefully experience and sharing this information will be beneficial to all (as well as discussion like these). Maybe it depends on who is learning Haskell, and why: maybe the 'conflict' is that learning to program *in* Haskell /= learning to program *with* Haskell. But maybe it's not ultimately an optimizable piece of data, the right order of teaching concepts in Haskell. Maybe it should be allowed to be more random-access? (I personally like things more that way :-) . Cheers Jared. -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: [1] Perhaps a point in Haskell's favor for pedagogy is that there are things you can do in Haskell that you just can't do (in the same, succint sense) in most programming languages, e.g. even OCaml. Maybe these things (and they are neat, simple things, like the code twos = 2:twos and then manipulating this infinite stream) can help motivate people to really want to grok Haskell, and to stick with it and use it for practical projects because of its many advantages. :-) [2] Paul Hudak does this in the Haskell School of Expression. He writes recursive code with cases, etc. and then in a later chapter explains how to rewrite it with map, fold, etc. Fine. It takes steps to learn how to write idiomatic Haskell. At least for me, the joy of Haskell is not in memorizing vocabulary (as is common in a language like Java, or C#) but rather, internalizing concepts. By writing ugly code at first and then seeing the patterns and refactoring with map and fold, I've personally internalized it (instead of learning some clever rule, up front, that I'll later forget). Think Why FP Matters by Hughes. He does this too (recursion, pattern matching, then later swapping in higher order functions), to explain why FP is so great. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FAQ: Why no interactive definitions?
There was a good discussion about this on an earlier thread. http://www.mail-archive.com/haskell-cafe@haskell.org/msg11372.html In fact, this exact question sparked a number of long threads. :-) (First steps in Haskell, Tutorial upload, Proposal for a First Tutorial.) Cheers, Jared. -- [EMAIL PROTECTED] http://www.updike.org/~jared/ reverse )-: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problems with square root...
MG () - Parenthesis
MG {} - Braces
MG [] - Brackets
MG Sorry to be pedantic, but using the wrong terminology confuses me and
MG I'm sure others as well.
This is true for Haskell, but Daniel is correct if he is calling ()
Brackets because they are, in British English, right? (Just like '.'
is a 'period' in US, but it is a 'full stop' in UK.). Of course,
English /= Haskell so in Haskell I guess they are called Parenthesized
Expressions (in the Haskell report
http://www.haskell.org/onlinereport/exps.html).
To be extra pedantic, I would call {} Curly Braces (or Curly Brackets,
or squiggly brackets, or squiggles, or ... just use layout and
whitespace!) and I would call [] Square Brackets. Then no one gets
confused.
Cheerio,
Jared
P.S. IANAA = I am an American, so I could very well be wrong about
British English!
On 12/21/05, Daniel Carrera [EMAIL PROTECTED] wrote:
Daniel Carrera wrote:
Hey,
The sqrt function is not doing what I want. This is what I want:
round sqrt(2)
Sigh... never fails. Spend an hour trying to solve a problem, and a
minute after you write to the list you find the solution. I need
brackets around sqrt. I'm surprised though. I don't understand why it
dosn't work without brackets.
Daniel.
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