Hi
I agree. = 1.0 isn't viable in the long term. Rather, a specific list,
or bounded range of tested versions seems likely to be more robust.
In general, if it compiles and type checks, it will work. It is rare
that an interface stays sufficiently similar that the thing compiles,
but then
Hi
Then, I set out to learn Monads + Category Theory from a Math
perspective.
This is where you went wrong. I know none of this stuff and am
perfectly happy with IO in Haskell. Read
http://www.haskell.org/haskellwiki/Monads_as_Containers and then read
lots of other Monad tutorials for Haskell.
Hi
main n = print . sum . map read . take n . reverse . lines = getContents
Could someone describe succinctly how to compute the space complexity of
this program, if there are m lines of input and m n? Many thanks. --PR
The space complexity is the size of the file - i.e. of size m. reverse
Hi Simon,
We are all familiar with the idea of an MD5 checksum, which provides a
reliable fingerprint for a file, usually 128 bits or so. If the file
changes, the fingerprint is (almost) certain to do so too. There are lots of
techniques: CRC, shar?, MD5, etc.
I believe the basic
Hi
The file you have requested
(http://www.cs.york.ac.uk/fp/cpphs-1.5-win32.zip) could not
be found on this server.
The slightly older version works:
http://www.cs.york.ac.uk/fp/cpphs-1.2-win32.zip
I'm unable to get SSH from this machine, so can't tell where that file
has gone to. Malcolm
Hi
In future questions like this are usually best directed to
haskell-cafe, with haskell being left for annoucements.
The standard full haskell representation is in Template Haskell
(http://haskell.org/ghc/docs/latest/html/libraries/template-haskell/Language-Haskell-TH.html).
If you want to work
Hi Peter,
Also typing runhugs Setup.hs configure fails with
runhugs: Error occurred
ERROR c:\program
files\winhugs\packages\base\Text\ParserCombinators\ReadP.hs:156
- Syntax error in type expression (unexpected `.')
This is because Cabal gets it wrong. You need to type runhugs -98
Setup
Hi Peter,
There is a Dotnet tree in the Hugs source code files, which I believe
is what supports dotnet. As far as I am aware, it probably won't work.
A windows developer may be able to build it, but I've never tried.
You might also be interested to know that Yhc supports --dotnet to
generate a
Hi Peter,
This is of course very easy to do manually, but does a command line tool
exist for extracting source code from literate Haskell files?
Cpphs is the perfect tool to do this.
Thanks
Neil
On 9/30/07, Peter Verswyvelen [EMAIL PROTECTED] wrote:
Thanks,
Peter
Hi Peter,
It sounds like the problem is that you need to convert it to Hugs,
rather than WinHugs specific (which might put a few people off looking
to see if they can help). Perhaps an email to the author of the
library might help you find if they would be interested in doing a
port to Hugs.
Hi
show_system =
unlines .
zipWith
(\l ms -
Eq ++
show l ++
: ++
(concat $ intersperse + $ zipWith (\n x - x ++ x ++ show
n) [1..] (init ms)) ++
= ++
last ms
)
[1..] .
map (map (take 8 . show))
And people complain that
Hi
complex. The input is quite simple (it's a bunch of numbers), the output
is quite simple (it's a neatly formatted string), but the process in the
middle is... a mess. I'd like to find a more readable way of doing stuff
like this. It's not just this specific function; any general hints
Hi
Forgive me, but I would much prefer a newsgroup to a mailing list.
True, I could unsubscribe now and just browse the mailman archives -
but for posting, I'd have to temporarily re-subscribe, which is awkward.
(Indeed that's the only reason I'm not doing it.)
I believe you can post from
Hi
Forgive me, but I would much prefer a newsgroup to a mailing list.
True, I could unsubscribe now and just browse the mailman archives -
but for posting, I'd have to temporarily re-subscribe, which is awkward.
(Indeed that's the only reason I'm not doing it.)
I believe you can post from
Hi Vimal,
I was surprised to find out that the following piece of code:
length [1..] 10
isnt lazily evaluated!
The problem is that Int and Integer are both eager. It is possible to
write a lazy peano number based data type, but I'm not aware of anyone
who has - I have half the code (in
Hi
In this world, use length (take 11 [1..]) 10...
not (null (drop 10 [1..])) is surely faster (not tested...)
Faster? There might be a few microseconds in it.
Clearer? Possibly... ;-)
lengthNat [1..] 10
Couldn't be clearer, and can be made to work perfectly. If anyone does
want to
Hi
lengthNat [1..] 10
Couldn't be clearer, and can be made to work perfectly. If anyone does
want to pick up the lazy naturals work, I can send over the code (or
write it yourself - its not hard!)
Um... isn't a lazy natural just a list with no data, where the list
length encodes a
Hi
Pretty much, yes.
So I just need to write
newtype LazyNatural = LazyNatural [()]
or
data Nat = Zero | Succ Nat
it's your choice really.
and then add some suitable instances. ;-)
Yes. Lots of them. Lots of instances and lots of methods.
Hey, the length function would then just
Hi
I'm guessing there's going to be fairly minimal performance difference.
(Or maybe there is. My way uses a few additional pointers. But it also
allows me to elegantly recycle existing Prelude list functions, so...)
I think we can safely assume that people using peano numbers aren't
actually
Hi
I'm not sure, but since it would require the detection of an evaluation
that does not terminate, it comes down to the halting problem, which is
not generally solvable. Maybe the experts can confirm my intuition?
I think your intuition is off. This isn't the problem of detecting
that a
Hi
The haskell-cafe@ mailing list is more appropriate for messages such
as this. haskell@ is just for announcements (it should be called
haskell-annouce@ !)
* Lambda calculus - the basis of functional languages
* Category theory - where all these mysterious things like monads,
arrows, and
Hi
I've just replied to another first poster with wrong list. Its
entirely not their fault, but its also probably a bit off-putting that
your very first post gets a (very polite) you got it wrong message.
To steal the reasons and explanations from Ian:
-
pretty much what
Hi
I agree. Unless... do some people subscribe to haskell@ (not
haskell-cafe@) and like the existing stuff that's sent there (not all
announcements... I'm not sure if I'd call e.g. Oleg's occasional
demonstrations announcements even)?
There are four things sent to the haskell list@
1)
Hi
f = f
and then try to evaluate 'f' in GHCi, as one would expect, the interpreter
never returns an answer.
The funny thing is that, while it is stuck in an infinite loop, GHCi doesn't
seem to use any CPU time at all.
It's called a black hole. The runtime can detect that f directly
All dependencies etc. have changed when going to 6.7/6.8 - you are
probably better off using 6.6.1 for now.
That's a petty. I really would like to experiment with the debugger :-)
Me too! A proper release of GHC 6.8 is very nearby, so you should get
your wish then.
Thanks
Neil
Hi
who has vty for haskell?
I can't find the right one so who can mail one to me ?
http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vty-3.0.0
hackage has a lot of packages, and is always a good place to start a search.
Thanks
Neil
___
Hi
Now why isn't pattern matching lazy by default? This seems odd for a
newbie since everything else is lazy by default.
f ~(x:xs) = rhs
f ~[] = rhs'
Now guess what f [] does...
If you use a where binding then pattern matching is lazy.
Thanks
Neil
Hi Peter,
During a googling session, I can across (Win)HIPE, a visualization program
for the functional language HOPE. See
http://dalila.sip.ucm.es/~cpareja/winhipe
IMHO a similar tool would be a nice for learning/teaching Haskell; does
that exist, or something else that comes close?
Hi
Yes, Hat does this http://www.haskell.org/hat/ (if you can get it to
work, I typically have little success)
Thanks. WinHIPE uses graphics and animation. If briefly encountered Hat
before, but I had the impression it did not visualize the graphs using
graphics, only text. Is this
Hi Peter,
So I grabbed ghc-6.7.20070824 (=the latest one for Windows I could find)
and the extra-libs, compiled and installed the GLUT package (which I
needed), but when I compile my library, I get
Could not find module `Data.Map':
it is a member of package containers-0.1,
Hi
What is the process for the inclusion of modules / packages in ghc, hugs and
other compilers interpreters?
Propose to have the packaged added. There is a very low chance of this
being accepted. The only packages to have recently been added were
FilePath and ByteString, both of which were
Hi
I think there is a niche for a subset of the hackage libraries providing
an officially sanctioned standard library collection. Currently,
hackage includes, well, everything. As such, it is a useful resource,
but it would be useful to have a partitioning into two levels, where the
SLC
Hi Barney,
This may be of interest, since all types already have an Int
associated with them:
http://haskell.org/ghc/docs/latest/html/libraries/base/Data-Typeable.html#v%3AtypeRepKey
Thanks
Neil
On 9/18/07, Barney Hilken [EMAIL PROTECTED] wrote:
In order to make my records system
Hi
okay, but this fails in some cases. i wrote a package to obtain
financial quotes. yahoo changed the webservice url on me. i rolled out
a change within a day. in your model, people suffer a broken service
for two weeks.
I don't think Yahoo will change the syntax or semantics of filepaths
Hi
Are you aware that Dimitry is still working on ycr2js - and has made
great progress. There are details available in The Monad Reader, issue
7 (http://www.haskell.org/haskellwiki/The_Monad.Reader)
Thanks
Neil
On 9/17/07, Victor Nazarov [EMAIL PROTECTED] wrote:
Hello.
I'm working on the
Hi
case e of b { pati - rhsi }
* evaluates 'e',
* binds the resulting value to 'b',
* performs case analysis on the result to find which alternative to choose
* binds the variables of the pattern to the components of the value
The Yhc.Core translator converts this to:
let b = e in case b
Hi
Would you care to explain why you have this aversion to libs that aren't
bundled with ghc?
They are less stable and have less quality control. It is also an
additional burden for a user to install the library to get the program
working.
cabal-install should fix the second. Some useful
Hi
What's bad about stagnation is that nobody will bother to produce
anything better (at least not as a fully polished publicly available
open source project), precisely because they have little chance of
achieving a user base exceeding 1 (at least not if the attitude of
David and Neil is
Hi
They are less stable and have less quality control.
Surely you jest? I see no evidence of this, rather the contrary in fact.
No, dead serious. The libraries have a library submission process.
Compare me changing my tagsoup library, to me changing my filepath
library which comes bundled
Hi
Monomorphism restriction? Replacing fold with foldRegsUsed would work
because there's a type signature for foldRegsUsed.
That looks like it. Another solution would be:
fold = foldRegsUsed
becomes:
fold x = foldRegsUsed x
Now the monomorphism restriction doesn't kick in because fold
Hi
Although I appluad the semantics of the safe package, I'm not delighted
with the idea of replacing our concise elegant standard library names
with uglyAndRatherLongCamelCaseNamesThatCouldBePerlOrEvenJava though.
Conciseness of expression is a virtue.
They aren't that long - merely an
Hi
Similarly, I expect foo and foo' to be equivalent, except for strictness
properties, but perhaps an underscore could be used for slightly
different behaviors (interpretations, as it were)? tail_ or zip_,
anyone?
There are 4 variants of tail:
tail :: [a] - [a] -- normal
tailDef :: [a] -
Hi
Is there a reason for not having
tailM :: Monad m = [a] - m [a]
which, at least for me, is much more useful?
No, that probably is a much more sensible choice. Patches welcome :)
Thanks
Neil
___
Haskell-Cafe mailing list
Hi
From the logical point of view tailMay is the right one.
It pushes the error handling to the caller programm.
tail = fromJust . tailMay
The error messages suffer:
tail [] = error: fromJust Nothing
That's why I supplied tailNote, where tailNote foo broke its
invariant! [] gives the
Hi
A more serious point is that in some cases we might want take to
underapproximate, or zip to truncate (or tail [] = [] ?). I don't
think there's
always a clear library choice here.
I have a zipWithEq function I often use, which crashes if the zip'd
lists aren't equal. I also have tailSafe
Hi
The same should apply to head and tail. head or tail of [] should be [].
What does the list think?
Disagree, strongly. Its not even possible for head, since [a] - a.
Wadler's theorems for free states that if head is given an empty list
the _only_ thing it can do is crash.
Thanks
Neil
Hi Peter,
The way I see it as a newcomer, Haskell shifts the typical imperical
programming bugs like null pointers and buffer overruns towards
space/time leaks, causing programs that either take exponentially long
to complete, stack overflow, or fill up the swap file on disc because
they
Hi
Well, I actually meant more something like the imperative equivalences
of code coverage tools and unit testing tools,
hpc and HUnit cover these two things pretty perfectly. hpc will be in
GHC 6.8, and its really cool :-)
because I've read
rumors that in Haskell, unit testing is more
Hi
there is no runtime representation of type available for programmatic
representation
Data.Typeable.typeOf :: Typeable a = a - TypeRep
there is no runtime representation of the type-inferencing or checking
machinery
Pretty much, no. The GHC API may provide some.
there is no runtime
Hi Peter,
It does not seem to have shortcut keys for reload, edit, etc...
When do you use reload? WinHugs automatically reloads modified files,
so I've never felt the need to reload things. Similarly for edit,
typing just edit on its own isn't that useful unless you give it a
module.
However,
Hi Peter,
Automatic reloading is of course THE best solution, and that's already
in :-) Maybe it could help new users to display a simple message into
the WinHugs statusbar like module XXX reloaded after external
modification at HH:MM:SS) or something? But that's really minor.
That would be
Hi
I've never really understood what the benefit of this is... I mean,
Google make the Google toolbar, but what's the point? Why not just
click on the Google bookmark and type in your search? What benefits does
installing a special addon provide?
You can setup firefox so in the location
Hi
I have the following page bookmarked:
http://haskell.org/ghc/docs/latest/html/libraries/
Just bookmark: http://haskell.org/hoogle
It's not perfect, but it probably solves lots of your problems.
A tip is to use Firefox's search as you type feature if you know the
module name.
This
Hi
(Some list operations are too expensive with ByteString but for most
string processing it's perfectly fine and much faster than String).
I'm sure it's true, but it's quite irrelevant to my question, which is
why is using getChar so much slower than using getContents?
Buffering, blocks
Hi
Re ! as an operator: This caused a number of complexities in the
parsing of stuff, including shift-reduce conflicts. Someone would need
to look into this, and determine that the rules are completely
unambiguous.
Backwards compatibility requires that it be implicitly imported from
Prelude
Hi Neil,
Given that GHC 6.8 is just around the corner and, given how it has
re-organised the libraries so that the dependencies in many (most/all)
the packages in the hackage DB are now not correct.
Is there a plan of how to get hackage DB up to speed with GHC 6.8 ?
I think whatever we go
Hi
* Create sophisticated GUIs.
Gtk2hs. Could do with a nice wrapper on that, but Conal is doing some
interesting stuff, and I've got PropLang on the back burner. People
are thinking the right thoughts, it just needs time.
* Read and write standard binary file formats. (Images, compressed
Hi
Data.Binary is the low level frameworks, now people can pick up the rest.
Last time I checked, there's about half a dozen binary packages. All
incompatible. All with different design. Seriously not obvious which one
to use...
Data.Binary is the answer,
Hi
Ouch, the well-known case-preserving but case-ignoring default behaviour
of MacOS X's file system bites someone again.
In short: Mac OS X's filesystem ignores case when opening a file, but
preserves
case when creating.
FWIW, Windows has exactly the same behaviour. Technically you can
Hi
Bring back HaWiki!
I couldn't agree more! We built up an incredible array of articles, by
fantastic authors with stunning content - which we then deleted... I
learnt much from the old wiki, and it would be a shame if others
didn't get that opportunity.
Of course it should be static only,
Hi
There are two entirely separate issues in this thread - let's not confuse them.
1) The old HaWiki content is good and unavailable. I want it made
available, in whatever form is appropriate. Please :-)
2) Licensing - the old content cannot be dumped onto the new wiki. My
personal view is who
Hi
I have just discovered Generics in Haskell and, writing some code with
GHC, I wondered about the portability of my code.
If you use Data.Generics, your code is not portable - no other Haskell
implementation supports the necessary bits.
I can use the -fgenerics to automatically derive
Hi
hello thanks for my new subscription, do I need to pay a fee or is it free
to join ?
This is a mailing list. Its totally free, and for the purpose of
discussing future improvements to the Haskell standard. If you just
wait, you'll find interesting discussions flowing into your inbox. If
Hi Alexteslin,
I just came across with this question on the exam and can not think of
implementing it.
mapPair :: (a - a - a) - [a] - [a]
such that mapPairs f [x1, x2, x3, x4...] = [f x1 x2, f x3 x4,...]
I would implement this using direct recursion. As a starting point,
the standard
Hi
mapPairs :: (a - a - a) - [a] - [a]
mapPairs f [x] = [x]
mapPairs f [] = []
mapPairs f (x:xs) = f x (head xs) : mapPairs f (tail xs)
It looks like it works, but you can get a better version by changing
the last line:
mapPairs f (x:y:zs) = ... - left as an exercise, but no need for head
Hi
- Blogging software. (Because there isn't enough of it in the world yet.)
Hope (google: Haskell Hope)
- A wiki program. (Ditto.)
Flippi (google: Haskell Flippi)
- A general CMS.
Hope
- An interactive function plotter. (GNUplot is nice, but it can't plot
recursive functions...)
None
Hi
Flippi (google: Haskell Flippi)
...and yet haskell.org uses WikiMedia? (Which is written in something
bizzare like Perl...)
Yes, but WikiMedia is a result of years of work, Flippi is a lot less.
Wikipedia uses WikiMedia - its a tried and proven solution.
- A graphical programming
Hi
Another option would be to port the yhi bytecode interpreter to run on
PalmOS. I tried this, but I ran into three problems:
1. libgmp dependency
This is no longer an issue, we now have a flag to not require libgmp,
which makes type Integer = Int
2. build system requires Python
Hi
I'm new to WinHugs, what's wrong with isUpper of my WinHugs?
Nothing. The book/tutorial you are going from is out of date. Before
using the isUpper/isLower functions you first have to type :load
Char:
Hugs :load Char
Hugs filter isUpper ABCDEfgh
ABCDE
The :load Char loads the Char module
Hi
Its (==) isn't
reflexive (is it transitive? probably, at least if there aren't too many
optimizations, but floating-point transitive equality isn't very useful).
It's not even referentially transparent in all cases. a == b may fail
while the double's are in the high precision registers,
Hi
Yeah, the precise details may vary, even :) But for teaching, an
automatic tool that does graph reduction would be great. I don't mind
if it's sloppy (directly apply definitions pattern matching VS
everything is a lambda abstraction) and only does simply typed lambda
calculus (no
Hi
Other rules that could be interesting are:
forall a b. fromInteger a + fromInteger b = fromInteger (a + b)
forall a b. fromInteger a * fromInteger b = fromInteger (a * b)
This is wrong, since the class function can do what it wants. Imagine:
instance Num String where
(+) = (++)
Hi
If Num obeys ring axioms, fromInteger is a perfectly fine
ring-homomorphism. (It's also the first or second homomorphism taught.)
Does Int obey these axioms? I'm thinking that assuming properties
about things such as numbers is very likely to go wrong very quickly.
Monads you might be able
Hi
factors :: Int - [Int]
factors n = [x | x - [1..n], n `mod` x == 0]
prime :: Int - Bool
prime n = factors n == [1, n]
My vague intuition said we either need factors or we don't, we do
because we need to perform the test, so we compute it. That's wrong,
so a posteriori the
Hi
Wait, you're saying that ghc can produce pure c-code, that doesnt
contain any assembly code, and that runs as fast as ghc code that does
contain assembly?
No. It can produce pure C code (unregistered), but to get high
performance it processes the output assembly afterwards (registered).
Hi Peter,
liftV1 f (V x y) = V (f x) (f y)
liftV2 f (V x1 y1) (V x2 y2) = V (f x1 x2) (f y1 y2)
liftM1 f (M x y) = M (f x) (f y)
liftM2 f (M x1 y1) (M x2 y2) = M (f x1 x2) (f y1 y2)
Both pairs of lift functions have almost identical implementations. Can I
Hi
sum (enum 1 10) =
sum' 0 (enum 1 10) =
...
sum' 36 (9 : enum (9+1) 10) =
(sum' $! (36+9)) (enum (9+1) 10) =
sum' 45 (enum (9+1) 10) =
sum' 45 [] =
45
(I need to find some way to automate making these trails
Hi
Distribution/Simple/InstallDirs.hs:267:36:
Not in scope: `dropDrive'
[EMAIL PROTECTED]:~/installs/cabal-head/caballs -l `which ghc`
lrwxrwxrwx 1 root root 31 2007-08-20 11:08 /usr/local/bin/ghc -
/usr/local/bin/ghc-6.7.20070816
You'll need to upgrade the filepath library as well,
Hi,
The Haskell desugaring for list comprehensions is given in:
http://haskell.org/onlinereport/exps.html#list-comprehensions
All the rules seem to be left to right rewrites, apart from the second
one, which seems to be right to left. Is there some deep reason for
this, or is this accidental.
Hi
Sorry for the noise, I've now realised they are a left to right
rewrite system, the second rule is required to set up the base case.
Thanks
Neil
On 8/19/07, Neil Mitchell [EMAIL PROTECTED] wrote:
Hi,
The Haskell desugaring for list comprehensions is given in:
http://haskell.org
Hi
will 6.7 be released, or will only 6.8 be ?
6.7 is the HEAD branch, 6.8 will be released.
-in that case, does the 6.8 branch means the freeze is on, and what would be
the target for 6.8 ? Q3/2007 ? Q4 ?
Soon, in the next month - according to latest targets/estimates.
( context: I am
Hi Peter,
A nice application. One suggestion: I would have implemented it so
that a maximum on one backward hyperlink menu could be visible at once
- try clicking on two RHS's and you'll get too menus visible at the
same time.
You also might want to mail this out on haskell-cafe - which is more
Hi
In addition, perhaps this should be relocated to haskell.org, if your
server is not suitable for a large volume of users. I think it should
also be integrated somewhere (perhaps a link from the HTML report, and
certainly on the wiki)
Thanks
Neil
On 8/16/07, Neil Mitchell [EMAIL PROTECTED
Hi
So what I noticed that A Gentle Introduction to Haskell mentioned
that wild-cards are useful in constructors. For example:
head (x:_) = x
So, does that offer any performance benefits over:
head (x:xs) = x
No. They are exactly the same. _ simply means a new unique name.
Or is it
Hi Dougal,
It's cross platform, and will use GHC and Hugs if they are already installed.
Thanks
Neil
On 8/15/07, Dougal Stanton [EMAIL PROTECTED] wrote:
On 15/08/07, Asumu Takikawa [EMAIL PROTECTED] wrote:
== GuiHaskell
Guihaskell is a graphical REPL using PropLang, a GUI combinator
Hi Simon,
OK this is an interesting one. Here's the smallest program that demonstrates
the problem.
foreign import ccall unsafe stdio.h getchar getchar :: IO CInt
f56 :: State# RealWorld - Int - Int
f56 s v2 = case (unIO getchar s) of
(# s' , v6 #) -
case v2 of
Hi
a) use hoogle (haskell.org/hoogle). You can use hoogle to find functions by
types. But I don't
know haw to create a query such as ... - Document - ...
Hoogle unfortunately doesn't do that very well, although that would be a
great feature.
Wait for version 4 :-) - I've added _ 's for
Hi
I by mistake defined a type which did not specify a data constructor
So the question is what are types with no constructors good for? A
simple example would be appreciated.
They are called phantom types, and can be used for ensuring properties
at the type level.
I wrote about them in a
Hi
If you just use Catch (http://www-users.cs.york.ac.uk/~ndm/catch/):
foo x
| x 0 = ...
| x == 0 = ...
| x 0 = ...
This gives an error. Something identical to this code is in
Data.FiniteMap, and indeed, when using floats and NaN's (or just silly
Ord classes) you can cause
Hi
Perhaps we need to cool this thread down a little bit, and refocus. I
personally choose never to use ++ as anything but a statement, since
my brain works that way. Other people find different things natural,
so can pick what they choose. The one thing you can guarantee is that
discussing it
do block, in left-to-right order.
Monadic expressions in let statements are allowed. Outside a do block,
monadic subexpressions are banned.
Despite all these complications, it's still a great idea, and would be
lovely to have!
Thanks
Neil and Tom
On 8/3/07, Neil Mitchell [EMAIL PROTECTED
Hi
Can you combine let and do?
do let x = (- a)
f x
Right. In effect, as a matter of fact, the notation
x - a
would become equivalent to
let x = (- a)
Hmm, interesting. Consider:
let x = 12
let x = (- x)
Currently, in let x = ... the x is in scope on the right hand
Hi
do { do { a; b}; c }
is still the same as
do { a; do { b; c } }
yes? no? perhaps? sometimes? how long did it take you?
I'm not entirely sure I understand the point here. The monad laws are
defined in terms of = and return. They have never had anything to do
with do,
Hi
let x = 12
let x = (- x)
Okay, so the desugaring process wouldn't terminate in that case! One
could either: (a) try to retain the equivalence in theory, but make it
illegal to use x in a monadic subexpression when defining x; (b) we
could abandon my claim that they are equivalent.
Hi
if you write :
let x = (-a):x
is it possible that is desugars into :
temp -a
let x = temp:x
that would'nt work ?
That would work, since 'a' doesn't refer to 'x'. I can't think of a
real example where it becomes an issue, but the scope within 'a' has
changed.
Also :
do case x of
Hi
do case x of
[] - return 1
(y:ys) - g y = \temp - f temp
See the rule about always binding to the previous line of a do block.
This case then violates that.
I assumed that the example was equivalent to :
do case x of
[] - return 1
(y:ys)
Hi
Catch (www.cs.york.ac.uk/~ndm/catch) can infer that certain uses of
numbers fit into the {Neg, Zero, One, Pos} abstraction - so for
example it can infer that length returns {Zero, One, Pos}, but not
Neg. If you then do:
xs !! length ys
It will detect that length ys is natural, and will be
Hi
I know that Audrey Tang (the Pugs project) has used hamming numbers
for this, see http://www.perl.com/lpt/a/959
Thanks
Neil
On 8/2/07, Jon Harrop [EMAIL PROTECTED] wrote:
Any suggestions for a perfect example that uniquely demonstrates the benefits
of the Haskell language compared to
Hi Chris,
I've heard Simon (Peyton-Jones) twice now mention the desire to be able
to embed a monadic subexpression into a monad.
I think this is a fantastic idea, please do so!
$( expr ) -- conflicts with template haskell
( - expr ) -- makes sense, and I think it's unambiguous
Hi
It will detect that length ys is natural, and will be safe. However,
if you pass any arbitrary value as the index to !! it will warn of a
possible pattern match error.
I hope catch doesn't actually think that's safe, because it's not - set
ys = xs = [1,2,3,4,5], you'll get an index
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