Re: [Haskell-cafe] Unnecessarily strict implementations
Hi, On 02.09.2010, at 01:35, Daniel Fischer wrote: It's not that it's not as non-strict as possible per se. (Sorry, had to :) It's that intersperse's current definition (in GHC at least) can cause a space leak. In this case, making the function less strict can cure it, in other cases, more strictness might be the solution. I would be very happy if you would share this example with me. I am looking for an example where the current implementation of intersperse or inits causes a space leak for quite a while now. On the other hand, we currently have intersect [] _|_ = [] and one of intersect _|_ [] and intersect [] _|_ must give _|_. Which one is a matter of choice. I am sorry for not being precise. You are right. But right now we have intersect xs [] = _|_ for every list xs terminated by _|_. But I suffices to evaluate xs to head normal to decide that the result should be []. That is, we could have intersect [] _|_ = [] and intersect (_|_:_|_) [] = [] or intersect [] (_|_:_|_) = [] and intersect _|_ [] = [] and the current implementation satisfies neither. And before that, the rule intersect [] _ = [] if the current behaviour of intersect [] should be retained. That's a deal. The implication (=) :: Bool - Bool - Bool is too strict as well. We have False = _|_ = _|_ as well as _|_ = True = _|_ while one of these cases could yield True. I'm not convinced either should (nor that they shouldn't). I think this is a matter of elegance rather than a matter of efficiency. In the same way as I prefer False _|_ = False over False _|_ = _|_ I prefer False = _|_ = True over False = _|_ = _|_ The last slide lists among the problems proposes undesirably inefficient functions (reverse). I wouldn't equate 'not minimally strict' with 'too strict'. Minimal strictness also can have negative effects, one must look at each case individually. I second this but in my opinion the minimally strict implementation should be the default if there is no reason against it. Cheers, Jan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HDBC-postgresql and safe/unsafe FFI calls
On Thu, Sep 2, 2010 at 1:00 AM, David Powell da...@drp.id.au wrote: Thanks Jason, I think I had read that - I quite enjoy Edward's posts. Re-reading, seems to confirm what I thought, most (all?) of the FFI calls in HDBC-postgresql should be changed to safe. Wouldn't that require thread safety on the part of libpq? Versions 8.4 and earlier requires the library to be configured with the option --enable-thread-safety, although version 9.0 has thread safety turned on by default. http://www.postgresql.org/docs/8.4/static/libpq-threading.html http://www.postgresql.org/docs/9.0/static/libpq-threading.html At least the Ubuntu PostgreSQL 8.4 packages are compiled with thread safety, but I can't speak for other distributions. Best, Leon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Linking issues with HaskellDB/HDBC/ODBC
Hi Anyone got any hints as to why this linkage error is occurring (GHC 6.12.3, Mac OSX 10.6 (and 10.5 has same issue)): cabal install haskelldb-hdbc-odbc --enable-documentation --root-cmd=sudo --global Resolving dependencies... Configuring haskelldb-hdbc-odbc-0.13... Preprocessing library haskelldb-hdbc-odbc-0.13... Preprocessing executables for haskelldb-hdbc-odbc-0.13... Building haskelldb-hdbc-odbc-0.13... [1 of 1] Compiling Database.HaskellDB.HDBC.ODBC ( Database/HaskellDB/HDBC/ODBC.hs, dist/build/Database/HaskellDB/HDBC/ODBC.o ) Registering haskelldb-hdbc-odbc-0.13... [1 of 2] Compiling Database.HaskellDB.HDBC.ODBC ( Database/HaskellDB/HDBC/ODBC.hs, dist/build/DBDirect-hdbc-odbc/DBDirect-hdbc-odbc-tmp/Database/HaskellDB/HDBC/ODBC.o ) [2 of 2] Compiling Main ( DBDirect.hs, dist/build/DBDirect-hdbc-odbc/DBDirect-hdbc-odbc-tmp/Main.o ) Linking dist/build/DBDirect-hdbc-odbc/DBDirect-hdbc-odbc ... Undefined symbols: _CFBundleCopyResourceURL, referenced from: _SQLDriverConnect_Internal in libodbc.a(connect.o) ___CFConstantStringClassReference, referenced from: cfstring=org.iodbc.core in libodbc.a(connect.o) cfstring=iODBCadm.bundle in libodbc.a(connect.o) _CFURLCopyFileSystemPath, referenced from: _SQLDriverConnect_Internal in libodbc.a(connect.o) _CFRelease, referenced from: _SQLDriverConnect_Internal in libodbc.a(connect.o) _SQLDriverConnect_Internal in libodbc.a(connect.o) _CFStringGetCString, referenced from: _SQLDriverConnect_Internal in libodbc.a(connect.o) _CFBundleGetBundleWithIdentifier, referenced from: _SQLDriverConnect_Internal in libodbc.a(connect.o) ld: symbol(s) not found collect2: ld returned 1 exit status cabal: Error: some packages failed to install: haskelldb-hdbc-odbc-0.13 failed during the building phase. The exception was: ExitFailure 1 Hints gratefully received!... Cheers Neil___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Thursday 02 September 2010 09:25:59, Jan Christiansen wrote:
Hi,
On 02.09.2010, at 01:35, Daniel Fischer wrote:
It's not that it's not as non-strict as possible per se. (Sorry, had
to :)
It's that intersperse's current definition (in GHC at least) can
cause a
space leak. In this case, making the function less strict can cure
it, in
other cases, more strictness might be the solution.
I would be very happy if you would share this example with me. I am
looking for an example where the current implementation of intersperse
or inits causes a space leak for quite a while now.
I don't see how the current implementation of inits or tails could cause a
space leak that the lazier versions wouldn't, so you'd have to wait longer
for such an example.
For intersperse,
$ cabal update cabal install stringsearch
You need the new version 0.3.1, Data.ByteString.Lazy.Search[.DFA].splitXXX
had their own space leak in 0.3.0 [caused by too much laziness].
Then
===
{-# LANGUAGE BangPatterns #-}
module Main (main) where
import System.Environment (getArgs)
import qualified Data.ByteString as S
import qualified Data.ByteString.Lazy as L
import qualified Data.ByteString.Char8 as C
import Data.ByteString.Lazy.Search (split)
main :: IO ()
main = do
(file : pat : sub : _ ) - getArgs
let !spat = C.pack pat
!ssub = L.fromChunks [C.pack sub]
work = ical ssub . split spat
L.readFile file = L.putStrLn . L.take 100 . work
ical :: L.ByteString - [L.ByteString] - L.ByteString
ical new = L.concat . intersperse new
intersperse :: a - [a] - [a]
intersperse sep [] = []
intersperse sep (x:xs) = x : go xs
where
go [] = []
go (y:ys) = sep : y : go ys
has no space leak, if you replace the local intersperse with
Data.List.intersperse (equivalent, ical = L.intercalate), you have a space
leak.
To expose the leak, take a sufficiently large file (say 10MB or larger) and
replace a pattern that does not occur in the file or occurs late in the
file,
$ ./noleak file pat sub
runs fast in small memory,
$ ./leak file pat sub
takes a little to run and keeps the entire file until the first occurrence
of pat in memory.
Note that the above implementation of intersperse has different semantics
from Data.List.intersperse,
Data.List.intersperse ',' ('a':_|_) = _|_
intersperse ',' ('a':_|_) = 'a':_|_
Data.List.intersperse ',' ('a':'b':_|_) = 'a' : ',' : _|_
intersperse ',' ('a':'b':_|_) = 'a' : ',' : 'b' : _|_
etc.
On the other hand, we currently have
intersect [] _|_ = []
and one of intersect _|_ [] and intersect [] _|_ must give _|_.
Which one is a matter of choice.
I am sorry for not being precise. You are right. But right now we have
intersect xs [] = _|_ for every list xs terminated by _|_. But I
suffices to evaluate xs to head normal to decide that the result
should be []. That is, we could have
intersect [] _|_ = [] and intersect (_|_:_|_) [] = []
or
intersect [] (_|_:_|_) = [] and intersect _|_ [] = []
and the current implementation satisfies neither.
Right. So the question is, has the current implementation advantages over
either of these? (I don't see any.) If not, which of these two behaviours
is preferable?
And before that, the rule intersect [] _ = [] if the current
behaviour of
intersect [] should be retained.
That's a deal.
The implication (=) :: Bool - Bool - Bool is too strict as well.
We
have False = _|_ = _|_ as well as _|_ = True = _|_ while one of
these cases could yield True.
I'm not convinced either should (nor that they shouldn't).
I think this is a matter of elegance rather than a matter of
efficiency. In the same way as I prefer
False _|_ = False
over
False _|_ = _|_
I prefer
False = _|_ = True
over
False = _|_ = _|_
I have mixed feelings about those. Part of me dislikes breaking the
symmetry between (=), (==) and compare.
The last slide lists among the problems
proposes undesirably inefficient functions (reverse).
I wouldn't equate 'not minimally strict' with 'too strict'.
Minimal strictness also can have negative effects, one must look at
each
case individually.
I second this but in my opinion the minimally strict implementation
should be the default if there is no reason against it.
Agreed - except I have to object to your use of the definite article, some
functions have several minimally strict implementations.
(Ambiguity of minimal strictness *can* be a reason for a stricter choice,
though probably rarely.)
Cheers, Jan
Cheers,
Daniel
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[Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
-- Haddock 2.8.0 A new version of Haddock, the Haskell documentation tool, is out! The biggest news this time is that we have a shiny new XHTML backend, created by Mark Lentczner, which outputs semantically correct XHTML, making it much easier to create new themes for Haddock. Mark has made an extraordinary effort by going through and rewriting the old table based HTML backend, fixing non-standards-compliant quirks, and adding a bunch of new useful features on top of that. See the changelog for more details. Included is a new default CSS theme created by Thomas Schilling, Mark and Johan Tibell, as well as the classic theme converted to work with the new backend. Another great new feature is markup support for examples, contributed by Simon Hengel. The idea is to be able to write examples that function both as documentation and unit tests. Last but not least, we now also have a LaTeX backend. It was written by Simon Marlow and it was used to generate the libraries section of the Haskell 2010 report. This version is compatible with .haddock files produced by Haddock 2.6.1 and above, provided that the version of GHC used to build Haddock stays the same. -- Changes in version 2.8.0 * HTML backend completely rewritten to generate semantically rich XHTML using the xhtml package. * New default CSS based on the color scheme chosen for the new Haskell wiki, with a pull-out tab for the synopsis. * Theme engine based on CSS files. Themes can be switched from the header menu. (New flags --built-in-themes and --theme. The latter is an alias for --css which now has extended semantics). * Markup support for executable examples/unit-tests. To be used with an upcoming version of the DocTest program. * Addition of a LaTeX backend. * Frames-mode can be enabled from the header menu. * Path to source entities can be specified per package, so that source links work for cross-package documentation. * Support for a second form of enumerated lists (1. 2. etc). * Additions and changes to the Haddock API. * New flag --no-tmp-comp-dir to tell Haddock to read/write compilation files (.o, .hi, etc) to/from GHC's output directory instead of to/from a temporary directory. * Various bug fixes. -- Links Homepage: http://www.haskell.org/haddock Hackage page: http://hackage.haskell.org/package/haddock-2.8.0 Bugtracker and wiki: http://trac.haskell.org/haddock Mailing list: hadd...@projects.haskell.org Code repository: http://code.haskell.org/haddock -- Contributors The following people contributed patches to this release: Simon Hengel Mark Lentczner Ian Lynagh Simon Marlow Simon Peyton-Jones Thomas Schilling David Waern -- Get Involved We would be very happy to get more contributors. To get involved, start by grabbing the code: http://code.haskell.org/haddock Then take a look at the bug and feature tracker for things to work on: http://trac.haskell.org/haddock ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] First questions!
Example 2 Prelude let fac n = if n == 0 then 1 else n * fac (n-1) How does it know to stop ? and why does fac 2.5 hang? thanks Eoin -- -- Eoin C. Bairéad Dublin, Ireland Áth Cliath, Éire ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: stringsearch 0.3.1, fast searching, splitting and replacing of ByteStrings
Changes vs. 0.3.0: - fixed a space leak in the splitting of lazy ByteStrings Changes of the 0.3 series vs. 0.2.*: - improved performance of the searching functions - new functionality: - breaking of ByteStrings at the first occurrence of a substring - splitting a ByteString at each occurrence of a substring - replacing all occurrences of a substring with another string Where bytestring provides the same functionality (Data.ByteString.breakSubstring, Data.ByteString.findSubstrings), the implementations in stringsearch are typically much faster. By default, stringsearch uses an enhanced Boyer-Moore algorithm to locate a pattern, but it also provides other algorithms which may be better in special cases (Knuth-Morris-Pratt; DFA). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First questions!
On Thursday 02 September 2010 14:49:12, Eoin C. Bairéad wrote: Example 2 Prelude let fac n = if n == 0 then 1 else n * fac (n-1) How does it know to stop ? It tests for n == 0. If that returns True, the recursion stops. and why does fac 2.5 hang? Because 2.5 is not an integer, so fac gets called with 2.5 1.5 0.5 -0.5 -1.5 -2.5 ... but never with 0, so you get infinite recursion. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First questions!
Hi! 2010/9/2 Eoin C. Bairéad ebair...@gmail.com Example 2 Prelude let fac n = if n == 0 then 1 else n * fac (n-1) How does it know to stop ? When fac is called with n=0 it returns 1 and stops the recursion. and why does fac 2.5 hang? fac, as you defined it, is only defined for integers. As you repeatedly subtract 1 from n you will never get to 0 (you will get to 0.5 and then -0.5) and thus the recursion will never terminate.\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
Jan Christiansen schrieb: Hi, On 02.09.2010, at 01:35, Daniel Fischer wrote: It's not that it's not as non-strict as possible per se. (Sorry, had to :) It's that intersperse's current definition (in GHC at least) can cause a space leak. In this case, making the function less strict can cure it, in other cases, more strictness might be the solution. I would be very happy if you would share this example with me. I am looking for an example where the current implementation of intersperse or inits causes a space leak for quite a while now. I'm also annoyed by several space leaks. These are implementation artifacts, but they seem to be hard to avoid by the existing implementations. You cannot reason about space leaks, right? That's a pity. I think this is a matter of elegance rather than a matter of efficiency. In the same way as I prefer False _|_ = False over False _|_ = _|_ I think this one is justified by the law: filter p (filter q xs) = filter (\x - q x p x) xs which only hold with the first definition of (). E.g. q x = x/=0 p x = div n x ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First questions!
02.09.2010 16:49, Eoin C. Bairéad пишет: Example 2 Prelude let fac n = if n == 0 then 1 else n * fac (n-1) How does it know to stop ? To stop what? It's not doing anything, it's just an equation. So fac is the least function which satisfies this equation - meaning that it's value would be (_|_) (which is a special value called bottom) whenever possible. When you ask for fac 3, for example, it's not possible for it to be (_|_), because it has to be 3*fac(2), according to this equation; and fac 2 isn't bottom either, because it has to be 2*fac(1); and fac(1) has to be 1*fac(0), which is also not bottom, because the equation states explicitly that fac 0 = 1. and why does fac 2.5 hang? Because there isn't anything to prevent fac 2.5 from being equal to (_|_); and when you ask for value that happens to be (_|_), your program can either crash or hang forever, it's the only special thing about bottom value. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] random-fu confusion
I seem to be having confusion at the runRVar level of random-fu. I can't figure out how to use the Data.Random.Source.PureMT module to get a meaningful random source (I can't get my code to type-check). I wrote a [trivial] flipCoin function flipCoin = uniform False True and am trying to fill in the final place of runRVar :t runRVar (replicateM 20 flipCoin) runRVar (replicateM 20 flipCoin) :: (RandomSource m s) = s - m [Bool] -- Alex R ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
On Sep 2, 2010, at 5:00 AM, David Waern wrote: -- Haddock 2.8.0 A new version of Haddock, the Haskell documentation tool, is out! The biggest news this time is that we have a shiny new XHTML backend, created by Mark Lentczner, ... Included is a new default CSS theme created by Thomas Schilling, Mark and Johan Tibell, as well as the classic theme converted to work with the new backend. If you'd like to see the new look in action, I've generated some pages for a few packages here: http://www.ozonehouse.com/mark/snap-xhtml/ - Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Sorry, my last message got garbled. Hope this is better. Prelude Control.Monad Control.Monad.Instances Control.Applicative let f = \x - x:[] Prelude Control.Monad Control.Monad.Instances Control.Applicative :t f f :: a - [a] Prelude Control.Monad Control.Monad.Instances Control.Applicative let g = \x - Just x Prelude Control.Monad Control.Monad.Instances Control.Applicative :t g g :: a - Maybe a = Prelude Control.Monad Control.Monad.Instances Control.Applicative let z = \x - x+1 Prelude Control.Monad Control.Monad.Instances Control.Applicative :t z z :: Integer - Integer Prelude Control.Monad Control.Monad.Instances Control.Applicative.Data.Char let y = \x - ord x Prelude Control.Monad Control.Monad.Instances Control.Applicative Data.Char :t y y :: Char - Int Can you think of a situation for \x - f x or \x y z - x + ord y - head z that would require x (y z) to have their type(s) declared (ala Pascal), or is it always inferred by what appears to the right of -? I guess what I'm asking is can an anonymous function be given a type signature? Michael --- On Wed, 9/1/10, Tillmann Rendel ren...@mathematik.uni-marburg.de wrote: From: Tillmann Rendel ren...@mathematik.uni-marburg.de Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Wednesday, September 1, 2010, 5:28 PM michael rice wrote: Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer So to create a value of type (Maybe ...), you can use Just. Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] So to create a value of type [...], you can use (:) and []. Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String So to create a value of type (IO ...), you can use getLine. Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] So to create a value of type (Either ... ...), you can use Right. How can I similarly create an instance of (-) [...] ? An instance of (-) is usually called a function. And functions are created by lambda abstraction: Prelude let f = \x - x Prelude :t f f :: t - t So to create a value of type (... - ...), you can use \. Just like Either, - is a binary type constructor. Just like (Either a b) is a type, (a - b) is a type. And very much like you can create (Either a b) values with Left and Right, you can create (a - b) values with \. Tillmann PS. After studying how to construct values, it may be instructive to study how to take them apart. For example, Bool values can be taken apart by if-then-else expressions. What about Either, IO and - values? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
On Thu, Sep 2, 2010 at 10:45 AM, michael rice nowg...@yahoo.com wrote: Can you think of a situation for \x - f x or \x y z - x + ord y - head z that would require x (y z) to have their type(s) declared (ala Pascal), or is it always inferred by what appears to the right of -? I think Haskell 98 can always infer the type of an anonymous function. There are some extensions involving more advanced types that can't be inferred, but you don't need to worry about them yet. I guess what I'm asking is can an anonymous function be given a type signature? Sure. Just write (\x - x + 1) :: Int - Int. (The parentheses are important. Without them, the type signature is given to the function body.) I don't think I've ever needed to give a type for an anonymous function, though. Generally, the context where the function is being used is sufficient. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: HDBC-postgresql and safe/unsafe FFI calls
Hi David, I've had varying arguments from people that want me to mark things safe or unsafe for various performance reasons. I'm happy to apply your change if you like. Can you send me a diff (and attach your explanation here to it, which I'll use as a commit message for future reference)? Thanks, -- John On 09/01/2010 09:40 PM, David Powell wrote: Greetings, I'm having an issue with the HDBC-postgresql package that requires me to manually patch it before installation for most of my use cases. All the FFI calls in this package are marked unsafe. Unfortunately, this means that whenever I issue a slow sql query, all other processing stops. In most places that I want to use this module, I've had to manually patch it to at least mark the PQexec and PQexecParams calls as safe. Is there any reason these calls should not be marked as safe? I understand that there a little extra runtime overhead with this, but I'd have thought that negligible given all the other processing that goes on with these particular calls under the hood. Cheers, -- David Powell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Thu, Sep 2, 2010 at 3:25 AM, Jan Christiansen j...@informatik.uni-kiel.de wrote: I prefer False = _|_ = True Sorry to go a bit off topic, but I find it funny that I never really noticed you could perform less-than or greater-than comparisons on Bool values. What's the semantic reasoning behind allowing relative comparisons on booleans? In what context would you use it? It seems to me a throwback to C's somewhat arbitrary assumption that False=0 and True=1. Steve ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Thu, 2 Sep 2010, Stephen Sinclair wrote: On Thu, Sep 2, 2010 at 3:25 AM, Jan Christiansen j...@informatik.uni-kiel.de wrote: I prefer False = _|_ = True Sorry to go a bit off topic, but I find it funny that I never really noticed you could perform less-than or greater-than comparisons on Bool values. What's the semantic reasoning behind allowing relative comparisons on booleans? In what context would you use it? You might use or abuse (=) for implication, however the arrow points to the wrong direction. It seems to me a throwback to C's somewhat arbitrary assumption that False=0 and True=1. My feeling is similar. The Ord instance for Bool might be justified for using Bools as keys of Data.Map, however you can also consider using Ord for Map as abuse.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On 02/09/10 17:10, Stephen Sinclair wrote: On Thu, Sep 2, 2010 at 3:25 AM, Jan Christiansen j...@informatik.uni-kiel.de wrote: I prefer False= _|_ = True Sorry to go a bit off topic, but I find it funny that I never really noticed you could perform less-than or greater-than comparisons on Bool values. What's the semantic reasoning behind allowing relative comparisons on booleans? In what context would you use it? It seems to me a throwback to C's somewhat arbitrary assumption that False=0 and True=1. Comparison on Bool itself is probably not particularly useful. But it is often useful if the Bool is part of a larger data structure. For example, I might want to have Set (String, Bool); without the Ord instance on Bool I couldn't do this. Similarly, you couldn't derive Ord on your data types that have Bool in them without the Ord Bool instance. Thanks, Neil. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Missing documentation in Haskell Platform on Windows
Arnaud Bailly wrote: Hello, I installed (succesfully) HAskell Platform 2010.2 on windows and have a small but annoying issue: Some links in HTML documentation lead to broken links. I did not investigate all the links, but I have seen that all doc under Control.Monad.XXX is missing. What am I doing wrong ? Almost every release of GHC that I can remember has had the links for the mtl package broken. (The Control.Monad.XXX modules are mostly from mtl. But, for example, Control.Monad.Fix is from base. I bet you'll find it works just fine.) Today I went and did a thorough check. HP 2009.2.x.x (I forget exactly which one) has links that point to C:\Program Files\Haskell Platform\2009.2.x.x\doc\ghc-mtl-x.x.x which does not exist. There is, however, a folder named C:\Program Files\Haskell Platform\2009.2.x.x\doc\mtl-x.x.x which exists just fine, and appears to contain the correct stuff. In HP 2010.1.0.0 and 2010.2.0.0, the links point to the latter address, but no such folder actually exists. The mtl documentation appears to simply be missing entirely, rather than being in a different place than where the links point to. Various older releases of GHC (before HP existed) have had one problem or the other, always with mtl, never with any other package. I have absolutely no idea why mtl is always broken, but all the other packages seem to work just fine. The fact that it happens so routinely suggests a problem with the build process rather than a one-off mistake. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Thursday 02 September 2010 18:25:11, Henning Thielemann wrote: The Ord instance for Bool might be justified for using Bools as keys of Data.Map, however you can also consider using Ord for Map as abuse. Why would one consider using Ord for Map an abuse? A kludge, for performance reasons, but an abuse? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] First questions!
Eoin C. Bairéad wrote: Example 2 Prelude let fac n = if n == 0 then 1 else n * fac (n-1) How does it know to stop ? Becuase you said if n == 0 then 1. In other words, if n is zero then return one and stop. Only if n does *not* equal zero does it recursively so n * fac (n-1). and why does fac 2.5 hang? Because the n == 0 condition never holds. fac 3 yields n=3, n=2, n=1, n=0, stop. fac 2.5 yeilds n=2.5, n=1.5, n=0.5, n=-0.5, n=-1.5... forever. Note carefully that fac (-6) also loops forever. Now, if you were to change the condition to n 1 rather than n == 0 then it would halt in all circumstances. You could also use a type signature to state that fac accepts only whole numbers, since this function only gives a meaningful answer in that case. (If you wanted a mathematically correct function, you need the Gamma function. But that's scary stuff, and this is a Haskell lesson not an advanced math lesson.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Missing documentation in Haskell Platform on Windows
andrewcoppin: Arnaud Bailly wrote: Hello, I installed (succesfully) HAskell Platform 2010.2 on windows and have a small but annoying issue: Some links in HTML documentation lead to broken links. I did not investigate all the links, but I have seen that all doc under Control.Monad.XXX is missing. What am I doing wrong ? Almost every release of GHC that I can remember has had the links for the mtl package broken. (The Control.Monad.XXX modules are mostly from mtl. But, for example, Control.Monad.Fix is from base. I bet you'll find it works just fine.) Well spotted, Andrew! The way to get things like this fixed is to report a bug to the relevant project. Click on the 'bug report' button: http://trac.haskell.org/haskell-platform/ You installed the Haskell Platform on Windows, so please mention this in the bug ticket. The problem will likely be in the Windows installer script, and what docs were bundled with that specific installer. Be as detailed in the report as you can, to make sure we can reproduce what trouble you have. In the meantime, you can always read the 'mtl' documentation on its package page: http://hackage.haskell.org/package/mtl -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On 10-09-02 12:10 PM, Stephen Sinclair wrote: Sorry to go a bit off topic, but I find it funny that I never really noticed you could perform less-than or greater-than comparisons on Bool values. What's the semantic reasoning behind allowing relative comparisons on booleans? In what context would you use it? It seems to me a throwback to C's somewhat arbitrary assumption that False=0 and True=1. A boolean algebra is also a lattice. The lattice order reflects implication. If the boolean algebra is furthermore 2-valued, the order is total too. The only possible dispute among people is over False=True vs True=False, i.e., should = be implies or implied by. But it is always correct to pick one and stick with it. This is useful wherever implication is useful. Suppose you wrote two functions and you now want to prove or quickcheck-test that they are extensionally equal, except you only care about arguments satisfying an assumption. You are checking (p x) implies (f x == g x) If you follow the Haskell choice, it is directly (p x) = (f x == g x) Implication is pervasively useful, but people pervasively underappreciate it; they avoid to think in terms of implication when the essence is implication. For example, some people say: you can use not (p x) || f x == g x. To that, I reply firstly: you can use solely NAND too, why don't you try that. And I reply secondly: implication is more direct, one single operator for the pervasive assume-guarantee paradigm, minimum boilerplate. There is no need to bring in negation. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Missing documentation in Haskell Platform on Windows
On Thursday 02 September 2010 19:34:07, Don Stewart wrote: andrewcoppin: Arnaud Bailly wrote: Hello, I installed (succesfully) HAskell Platform 2010.2 on windows and have a small but annoying issue: Some links in HTML documentation lead to broken links. I did not investigate all the links, but I have seen that all doc under Control.Monad.XXX is missing. What am I doing wrong ? Almost every release of GHC that I can remember has had the links for the mtl package broken. (The Control.Monad.XXX modules are mostly from mtl. But, for example, Control.Monad.Fix is from base. I bet you'll find it works just fine.) Well spotted, Andrew! The way to get things like this fixed is to report a bug to the relevant project. Click on the 'bug report' button: http://trac.haskell.org/haskell-platform/ You installed the Haskell Platform on Windows, so please mention this in the bug ticket. The problem will likely be in the Windows installer script, and what docs were bundled with that specific installer. Probably not. I'm on Linux and build my GHCs from source. There's no directory mtl-1.1.0.2 in ~/share/doc/ghc/html/libraries although it's linked to from the package index built with the compiler. (Hadn't noticed before because I use the index in ~/.cabal). Seems to be a slip-up in the makefiles. Be as detailed in the report as you can, to make sure we can reproduce what trouble you have. In the meantime, you can always read the 'mtl' documentation on its package page: http://hackage.haskell.org/package/mtl -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Missing documentation in Haskell Platform on Windows
On Thursday 02 September 2010 20:05:12, Daniel Fischer wrote: Probably not. I'm on Linux and build my GHCs from source. There's no directory mtl-1.1.0.2 in ~/share/doc/ghc/html/libraries although it's linked to from the package index built with the compiler. (Hadn't noticed before because I use the index in ~/.cabal). Seems to be a slip-up in the makefiles. Also broken: utf8-string haskeline terminfo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
2010/9/2 Mark Lentczner ma...@glyphic.com: On Sep 2, 2010, at 5:00 AM, David Waern wrote: If you'd like to see the new look in action, I've generated some pages for a few packages here: http://www.ozonehouse.com/mark/snap-xhtml/ Is it possible to switch back from frame version to non frame version? The Frames button disappears in frame mode... Also style changing works only inside the main frame. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
In each case, what does the notation show:: ... and undefined:: ... accomplish? Prelude Control.Applicative :t show::((-) Int) String show::((-) Int) String :: Int - String Prelude Control.Applicative :t undefined::((-) Int) String undefined::((-) Int) String :: Int - String Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 4:17 PM FmapFunc is just a test module I created with instance Functor ((-) r) where ... -- ryan On Tue, Aug 31, 2010 at 12:03 PM, michael rice nowg...@yahoo.com wrote: Hi, Ryan and all, Bingo! I guess my question was all right after all. I tried creating an instance earlier but *Main :t (-) Int Char interactive:1:1: parse error on input `-' What got loaded with FmapFunc? I Hoogled it and got back nothing. Michael --- On Tue, 8/31/10, Ryan Ingram ryani.s...@gmail.com wrote: From: Ryan Ingram ryani.s...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: Vo Minh Thu not...@gmail.com, haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 2:36 PM Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String Prelude FmapFunc let v = fmap (hello ++) s Prelude FmapFunc :t v v :: Int - String Prelude FmapFunc v 1 hello 1 -- ryan On Tue, Aug 31, 2010 at 11:28 AM, michael rice nowg...@yahoo.com wrote: I'm not sure if my terminology is correct or even if my question makes sense, but I can create instances of Maybe, List, IO, and Either. Prelude Data.Either let m = Just 7 Prelude Data.Either :t m m :: Maybe Integer Prelude Data.Either let l = 2:[] Prelude Data.Either :t l l :: [Integer] Prelude Data.Either let g = getLine Prelude Data.Either :t g g :: IO String Prelude Data.Either let e = Right abc Prelude Data.Either :t e e :: Either a [Char] All these instances are functors, each with its own version of fmap that can be applied to it. How can I similarly create an instance of (-) so I can apply (-)'s version of fmap instance Functor ((-) r) where fmap f g = (\x - f (g x)) to it? Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:50 PM 2010/8/31 michael rice nowg...@yahoo.com So it's a type constructor, not a type? Could you please provide a simple example of its usage? Sure, although I'm sure you've come by some already. -- the identity function id :: a - a -- often, we write it like this: -- id x = x -- but here we see the relationship between the ananymous function syntax and the function type: id = \x - x In fact, if you write in prefix form, it is quite familiar: f :: (-) Int Bool e = Either String Float Cheers, Thu Michael --- On Tue, 8/31/10, Vo Minh Thu not...@gmail.com wrote: From: Vo Minh Thu not...@gmail.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Tuesday, August 31, 2010, 1:17 PM 2010/8/31 michael rice nowg...@yahoo.com Learn You a Haskell ... says that (-) is a type just like Either. Where can I find its type definition? You can't define it *in* Haskell as user code. It is a built-in infix type constructor (Either or Maybe are type constructors too, not just types). In fact, if you want to implement a simple, typed functional language, you'll find it is the only built-in type constructor you have to implement (as the implementor of the language). Also, Show a = a is a type too, but you won't find a definition for 'a' or for '='. All those things are defined by the language. Cheers, Thu ___ 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] Missing documentation in Haskell Platform on Windows
On Thu, Sep 2, 2010 at 8:20 PM, Daniel Fischer daniel.is.fisc...@web.de wrote: On Thursday 02 September 2010 20:05:12, Daniel Fischer wrote: Probably not. I'm on Linux and build my GHCs from source. There's no directory mtl-1.1.0.2 in ~/share/doc/ghc/html/libraries although it's linked to from the package index built with the compiler. (Hadn't noticed before because I use the index in ~/.cabal). Seems to be a slip-up in the makefiles. Also broken: utf8-string haskeline terminfo Note that on Hackage all links in haddock pages to the current base library (4.2.0.2) are broken. Possibly because the documentation for base-4.2.0.2 was not build. The docs for base-4.2.0.1 are build fine: http://hackage.haskell.org/package/base Regards, Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
On Sep 2, 2010, at 11:30 AM, michael rice wrote: In each case, what does the notation show:: ... and undefined:: ... accomplish? They're type annotations. show is a function in many types: Prelude :t show show :: (Show a) = a - String If you want to see the type of a specific show function, you need to find a way to determine its type. This is a slightly different function, but it's equivalent in types and semantics: Prelude :t \x - show x \x - show x :: (Show a) = a - String Now we have a named argument, and we can constraint its type with an annotation: Prelude :t \x - show (x :: Int) \x - show (x :: Int) :: Int - String ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Projects that could use student contributions?
There is a lot of room for improvement to my NumberSieves package. The package consists of algorithms I extracted and polished up from when I was working on Project Euler problems. It makes solving a number of problems into quick five minute affairs. At some point I would probably do it myself, but I don't have a pressing reason to do it. http://hackage.haskell.org/package/NumberSieves Possible Improvements I have in mind: 1. Make things faster 2. Reduce memory requirements 3. Parallelize the sieves 4. Incrementalize the Factor and Phi sieves, so that an explicit upper bound is no longer required 5. Remove limitations so that Factor and Phi can sieve beyond 2^32 It would be a small and self-contained project, suitable for anybody who has an interest in Haskell and mathematics! If somebody is interested, by all means contact me via email, and I will share the approach I had in mind. Best, Leon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Thu, 2 Sep 2010 19:30:17 +0200, Daniel Fischer daniel.is.fisc...@web.de wrote: Why would one consider using Ord for Map an abuse? A kludge, for performance reasons, but an abuse? Because it forces one to declare Ord instances for types which have no natural ordering. It is useful to *not* have such instances, in order to catch programming errors. A separate type class for types which can be ordered in some (possibly arbitrary) way, for use in Data.Map, would remedy this. Regards, Arie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Multicore speedup and spark conversion with ghc HEAD
Follows three runs of a stupid program that should see a speedup (I believe). 1. Compiled with ghc-6.12.3. Run on 1 thread, 4.0 s (real). 2. Compiled with ghc-6.12.3. Run on 2 threads, spark converted, 5.4 s (real), 7.7 s (user). 3. Compiled with ghc-6.13.20100831. Run on 2 threads, but spark *not* converted 4.1 s (real). All runs with disabled parallel GC, which negatively impacts -N2 runs (whether the spark is converted or not). Two questions: A. Why is run (2) slower than (1)? GC is a bit more expensive, as one would expect, but not enough to explain the difference (only explains 0.3 s). B. ghc HEAD doesn't convert the spark. Why is that? Thanks. module Main where import Control.Parallel fac :: Integer - Integer fac n = aux n 1 where aux 0 _ = 0 aux 1 m = m aux n m = let p = n * m in p `pseq` aux (n - 1) p main = do let x = fac 10 y = fac 11 in print (x `par` y `pseq` (x + y)) $ ghc-6.12.3 -O2 -threaded -rtsopts Test.hs --make $ time ./Test +RTS -N1 -qg -sstderr /dev/null ./Test +RTS -N1 -qg -sstderr 20,460,660,928 bytes allocated in the heap 2,492,368 bytes copied during GC 462,128 bytes maximum residency (3 sample(s)) 76,576 bytes maximum slop 4 MB total memory in use (1 MB lost due to fragmentation) Generation 0: 35093 collections, 0 parallel, 0.14s, 0.17s elapsed Generation 1: 3 collections, 0 parallel, 0.00s, 0.00s elapsed MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 0.00s) 0.00s( 0.00s) Task 1 (worker) :0.00s( 3.84s) 0.00s( 0.00s) Task 2 (bound) :3.87s( 3.84s) 0.14s( 0.17s) SPARKS: 1 (0 converted, 1 pruned) INIT time0.00s ( 0.00s elapsed) MUT time3.83s ( 3.84s elapsed) GCtime0.14s ( 0.17s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time3.97s ( 4.02s elapsed) %GC time 3.6% (4.3% elapsed) Alloc rate5,345,814,403 bytes per MUT second Productivity 96.4% of total user, 95.2% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].steps[0].sync_large_objects: 0 gen[0].steps[1].sync_large_objects: 0 gen[1].steps[0].sync_large_objects: 0 real0m4.022s user0m3.970s sys 0m0.051s $ time ./Test +RTS -N2 -qg -sstderr /dev/null ./Test +RTS -N2 -qg -sstderr 20,600,461,512 bytes allocated in the heap 3,585,432 bytes copied during GC 458,480 bytes maximum residency (14 sample(s)) 76,576 bytes maximum slop 5 MB total memory in use (1 MB lost due to fragmentation) Generation 0: 34803 collections, 0 parallel, 0.43s, 0.48s elapsed Generation 1:14 collections, 0 parallel, 0.00s, 0.00s elapsed MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 0.00s) 0.00s( 0.00s) Task 1 (worker) :3.72s( 4.91s) 0.24s( 0.25s) Task 2 (bound) :3.91s( 4.91s) 0.19s( 0.23s) Task 3 (worker) :0.00s( 4.91s) 0.00s( 0.00s) SPARKS: 1 (1 converted, 0 pruned) INIT time0.00s ( 0.00s elapsed) MUT time7.29s ( 4.91s elapsed) GCtime0.43s ( 0.48s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time7.72s ( 5.39s elapsed) %GC time 5.6% (8.9% elapsed) Alloc rate2,824,733,790 bytes per MUT second Productivity 94.4% of total user, 135.2% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].steps[0].sync_large_objects: 0 gen[0].steps[1].sync_large_objects: 0 gen[1].steps[0].sync_large_objects: 0 real0m5.397s user0m7.724s sys 0m0.443s $ ghc-6.13.20100831 -O2 -threaded -rtsopts Test.hs $ time ./Test +RTS -N2 -qg -sstderr /dev/null ./Test +RTS -N2 -qg -sstderr 20,458,286,584 bytes allocated in the heap 2,705,816 bytes copied during GC 463,520 bytes maximum residency (3 sample(s)) 73,032 bytes maximum slop 5 MB total memory in use (1 MB lost due to fragmentation) Generation 0: 35088 collections, 0 parallel, 0.19s, 0.22s elapsed Generation 1: 3 collections, 0 parallel, 0.00s, 0.00s elapsed MUT time (elapsed) GC time (elapsed) Task 0 (worker) :0.00s( 0.00s) 0.00s( 0.00s) Task 1 (worker) :0.00s( 3.92s) 0.00s( 0.00s) Task 2 (bound) :3.90s( 3.92s) 0.19s( 0.22s) Task 3 (worker) :0.00s( 3.92s) 0.00s( 0.00s) SPARKS: 1 (0 converted, 1 pruned) INIT time0.00s ( 0.00s elapsed) MUT time3.84s ( 3.92s elapsed) GCtime0.19s ( 0.22s elapsed) EXIT time0.00s ( 0.00s elapsed) Total time4.03s ( 4.14s elapsed) %GC time 4.7% (5.2% elapsed) Alloc rate5,329,874,595 bytes per
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
On Thu, 02 Sep 2010 14:00:56 +0200, David Waern david.wa...@gmail.com
wrote:
-- Haddock 2.8.0
A new version of Haddock, the Haskell documentation tool, is out!
It doesn't install on Windows + MinGW:
cabal install --global haddock
Resolving dependencies...
Downloading haddock-2.8.0...
:
:
[ 9 of 33] Compiling Haddock.Utils( src\Haddock\Utils.hs,
dist\build\Haddock\Utils.o )
src\Haddock\Utils.hs:435:8: parse error on input `import'
cabal: Error: some packages failed to install:
haddock-2.8.0 failed during the building phase. The exception was:
ExitFailure 1
This concerns a line with a foreign import:
#ifdef mingw32_HOST_OS
foreign import ccall unsafe _getpid getProcessID :: IO Int -- relies on
Int == Int32 on Windows
#else
getProcessID :: IO Int
getProcessID = fmap fromIntegral System.Posix.Internals.c_getpid
#endif
Adding the line:
{-# LANGUAGE ForeignFunctionInterface #-}
to the top of file src\Haddock\Utils.hs helped.
Regards,
Henk-Jan van Tuyl
--
http://Van.Tuyl.eu/
http://members.chello.nl/hjgtuyl/tourdemonad.html
--
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Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
2010/9/2 Henk-Jan van Tuyl hjgt...@chello.nl:
On Thu, 02 Sep 2010 14:00:56 +0200, David Waern david.wa...@gmail.com
wrote:
-- Haddock 2.8.0
A new version of Haddock, the Haskell documentation tool, is out!
It doesn't install on Windows + MinGW:
cabal install --global haddock
Resolving dependencies...
Downloading haddock-2.8.0...
:
:
[ 9 of 33] Compiling Haddock.Utils ( src\Haddock\Utils.hs,
dist\build\Haddock\Utils.o )
src\Haddock\Utils.hs:435:8: parse error on input `import'
cabal: Error: some packages failed to install:
haddock-2.8.0 failed during the building phase. The exception was:
ExitFailure 1
This concerns a line with a foreign import:
#ifdef mingw32_HOST_OS
foreign import ccall unsafe _getpid getProcessID :: IO Int -- relies on
Int == Int32 on Windows
#else
getProcessID :: IO Int
getProcessID = fmap fromIntegral System.Posix.Internals.c_getpid
#endif
Adding the line:
{-# LANGUAGE ForeignFunctionInterface #-}
to the top of file src\Haddock\Utils.hs helped.
Thanks for catching this!
I'll wait a little while in case other issues are reported before I
upload 2.8.1.
David
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[Haskell-cafe] creating a type based on a string
I have a user input (string) and need to select one of two types. depending what the input is. is this possible? data A data B data X n = X String op :: String - X n op a = X a :: X A op b = X b :: X B this does obviously not compile. is there a way to achieve that the type X A is produced when the input is a and X B when the input is b? thank you for help! andrew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] creating a type based on a string
What is stopping you from using an enumeration type? data Tag = A | B data X = X String Tag op a = X a A op b = X b B On 9/2/10 1:31 PM, Andrew U. Frank wrote: I have a user input (string) and need to select one of two types. depending what the input is. is this possible? data A data B data X n = X String op :: String - X n op a = X a :: X A op b = X b :: X B this does obviously not compile. is there a way to achieve that the type X A is produced when the input is a and X B when the input is b? thank you for help! andrew ___ 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] creating a type based on a string
What you're asking for is essentially a dependent type (something where a
type depends on a value). Haskell doesn't support these, but can approximate
them with GADTs:
{-# LANGUAGE GADTs, EmptyDataDecls, KindSignatures, Rank2Types #-}
data A
data B
-- The data constructors refine the type index
data X :: * - * where
A :: X A
B :: X B
-- We can't return a different type based on the input string (unless you
represent the string as some complex GADT that itself refines the output
type), so instead we have a pseudo-existential type represented as a
polymorphic function parameter.
-- This basically says, if you give me a string and a function that can
work on X n for all values of n, I'll give you something of the same type as
the return value of that function
op :: String - (forall n. X n - r) - r
op a f = f A
op b f = f B
If you give a more detailed example of what you need, we might be able to
tell you better approaches, though. This rank-2/existential approach is
mostly useful for preserving internal (hidden from the end-user) type-level
constraints on GADT indices.
On Thu, Sep 2, 2010 at 10:31 PM, Andrew U. Frank
fran...@geoinfo.tuwien.ac.at wrote:
I have a user input (string) and need to select one of two types.
depending what the input is. is this possible?
data A
data B
data X n = X String
op :: String - X n
op a = X a :: X A
op b = X b :: X B
this does obviously not compile. is there a way to achieve that the type
X A is produced when the input is a and X B when the input is b?
thank you for help!
andrew
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[Haskell-cafe] Re: Crypto-API is stabilizing
Marcel noted: A central interface to get the output of a PRNG would be nice, preferably not constrained to Int like RandomGen. While BOS said: Also, don’t use RandomGen for your asymmetric PRNG. The default implementation in System.Random gives absolutely disastrous performance, and the typeclass is just misdesigned (the split function shouldn’t be present). Ok, ok. I never liked RandomGen either - I start this whole thing because of my PRNG and it doesn't fit RandomGen one bit. I've build Data.Crypto.Random.RandomGenerator - a new class that fixes the aspects of RandomGen I don't like. This is something I was considering anyway, so it's probably best now and not as an API upset in a couple months. There is a blog on this [1], but the main points about the new class are: 1) Generates bytestrings, not Ints 2) Generalized PRNG construction and reseeding 3) 'split' is in a different class. 4) Clean failure via Either (RandomGen forced you to use exceptions) And minor points - Providing additional entropy while requesting data is allowed and has a default instance so most users can ignore this all together. - a newtype wrapper and instance allows all RandomGenerator instances to be used as RandomGen when needed. Who cares about this? Anyone wanting to get random IVs for block cipher modes (without getIV_IO) and anyone wanting to generate asymmetric keys using the AsymCipher class. What can you do? Accept this API, help improve the API, or argue that we should stick with RandomGen (despite short-comings noted on the blog). Please pick one and get to it! Cheers, Thomas P.S. I would like to get crypto-api onto hackage by the end of the first week of September, but understand this is a fairly large change and will slide that date if there is an unusual strong objection. [1] http://tommd.wordpress.com/2010/09/02/a-better-foundation-for-random-values-in-haskell/ Designing a random interface that provides something as high a level as monad random, is easy enough to make instances for (like RandomGen) and is feature rich enough to allow reseeding, additional entropy input, personalization, and failure is a non-trivial design task. Having ran into the dilemma of how to provide a reasonable high-level interface for DRBG, I agree with your statement but don't know how a solution would look. FYI, BOS had a similar suggestion (on the blog) of moving away from RandomGen but I'm not clear on what I'd move toward. Cheers, Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Crypto-API is stabilizing
On Aug 27, 2010, at 11:12 AM, Heinrich Apfelmus wrote:
Is it actually necessary to use a type class here? The situation is
very similar to
Luke Palmer. Haskell Antipattern: Existential Typeclass.
http://lukepalmer.wordpress.com/2010/01/24/
I suggest to use good old data types
data Key = Key {
encrypt :: B.ByteString - B.ByteString,
decrypt :: B.ByteString - B.ByteString,
keyLength :: BitLength,
serialize :: B.ByteString}
rsa :: RandomGen g = BitLength - g - ((Key,Key), g)
In general, I like this approach, but what are
encrypt privateKey
or
decrypt publicKey
supposed to do? A type-class solution also does not *prevent*
programmers to perform such non-sensical calls, but the data-type
solution *forces* programmers to provide non-sensical encrypt and
decrypt functions when creating the public and private keys.
class (Binary p, Serialize p) = AsymCipher p where
generateKeypair :: RandomGen g = g - BitLength - Maybe
((p,p),g)
encryptAsym :: p - B.ByteString - B.ByteString
decryptAsym :: p - B.ByteString - B.ByteString
asymKeyLength :: p - BitLength
Why not use
generateKeypair :: MonadRandom m = BitLength - m (Maybe (p,p))
where MonadRandom is from [1].
Sebastian
[1]: http://hackage.haskell.org/package/MonadRandom
--
Underestimating the novelty of the future is a time-honored tradition.
(D.G.)
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Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
2010/9/2 Daniel Peebles pumpkin...@gmail.com: Mmm, delicious! Thanks to all involved! Any idea how long it'll take for this to make it to hackage and regenerate all the documentation up there? It'd be wonderful to do the same to the GHC documentation too. I don't actually know yet if it's possible to regenerate the documentation on hackage. We're looking into the matter. David ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Crypto-API is stabilizing
On Sep 3, 2010, at 12:07 AM, Sebastian Fischer wrote: Why not use generateKeypair :: MonadRandom m = BitLength - m (Maybe (p,p)) Or if the choice to generate keys or not should solely depend on the BitLength (and not on the random generator): generateKeypair :: MonadRandom m = BitLength - Maybe (m (p,p)) -- Underestimating the novelty of the future is a time-honored tradition. (D.G.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
Hi, On 02.09.2010, at 13:41, Daniel Fischer wrote: takes a little to run and keeps the entire file until the first occurrence of pat in memory. first of all thanks very much for the detailed instructions. I have rewritten the example slightly using Strings instead of Bytestrings. Replacing all occurrences of 'ä' by auml; in the collected works of Shakespeare ; ) has a maximum memory usage of around 65MB with the current implementation of intersperse while it has a maximum memory usage of only around 5KB with the less strict implementation. replaceBy :: Eq alpha = alpha - [alpha] - [alpha] - [alpha] replaceBy x sep = concat . intersperse sep . splitBy (==x) splitBy :: (alpha - Bool) - [alpha] - [[alpha]] splitBy _ [] = [] splitBy p xs = case break p xs of (l,ys) - l : case ys of [] - [] (_:zs) - splitBy p zs This function only runs in constant space if I use the strict pattern matching on the result of break. If I use the following implementation I observe a linear memory usage instead. splitBy' :: (alpha - Bool) - [alpha] - [[alpha]] splitBy' _ [] = [] splitBy' p xs = l : case ys of [] - [] (_:zs) - splitBy' p zs where (l,ys) = break p xs I think this is due to the Wadler tuple space leak. The same would apply to the current implementation of lines. I wonder whether an implementation of lines analogous to splitBy has any disadvantages. That is, we could have intersect [] _|_ = [] and intersect (_|_:_|_) [] = [] or intersect [] (_|_:_|_) = [] and intersect _|_ [] = [] and the current implementation satisfies neither. Right. So the question is, has the current implementation advantages over either of these? (I don't see any.) If not, which of these two behaviours is preferable? I'd prefer the first one as it is in line with the left to right pattern matching of Haskell. I have mixed feelings about those. Part of me dislikes breaking the symmetry between (=), (==) and compare. I think you should not blame (=) for the existence of a function that yields a superset of the information that (=) yields ; ) Cheers, Jan___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] creating a type based on a string
On Thu, Sep 2, 2010 at 9:31 PM, Andrew U. Frank fran...@geoinfo.tuwien.ac.at wrote: I have a user input (string) and need to select one of two types. depending what the input is. is this possible? data A data B data X n = X String op :: String - X n op a = X a :: X A op b = X b :: X B this does obviously not compile. is there a way to achieve that the type X A is produced when the input is a and X B when the input is b? thank you for help! andrew ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe Here's another way of not quite doing what you want: op :: String - Either (X A) (X B) op a = Left (X a) op b = Right (X b) which is roughly how I translate the recent discussion about type-level validity certification: http://www.haskell.org/pipermail/haskell-cafe/2010-August/082899.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Hi Alexander, Prelude FmapFunc let s = show :: ((-) Int) String Prelude FmapFunc :t s s :: Int - String The notation was throwing me, but after staring at it for a while it finally sunk in that show (above) is partially applied. Thanks, all. Michael --- On Thu, 9/2/10, Alexander Solla a...@2piix.com wrote: From: Alexander Solla a...@2piix.com Subject: Re: [Haskell-cafe] On to applicative To: Cc: haskell-cafe Cafe haskell-cafe@haskell.org Date: Thursday, September 2, 2010, 2:46 PM On Sep 2, 2010, at 11:30 AM, michael rice wrote: In each case, what does the notation show:: ... and undefined:: ... accomplish? They're type annotations. show is a function in many types: Prelude :t showshow :: (Show a) = a - String If you want to see the type of a specific show function, you need to find a way to determine its type. This is a slightly different function, but it's equivalent in types and semantics: Prelude :t \x - show x\x - show x :: (Show a) = a - String Now we have a named argument, and we can constraint its type with an annotation: Prelude :t \x - show (x :: Int)\x - show (x :: Int) :: Int - String -Inline Attachment Follows- ___ 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] Unnecessarily strict implementations
On Friday 03 September 2010 00:22:14, Jan Christiansen wrote: Hi, On 02.09.2010, at 13:41, Daniel Fischer wrote: takes a little to run and keeps the entire file until the first occurrence of pat in memory. first of all thanks very much for the detailed instructions. I have rewritten the example slightly using Strings instead of Bytestrings. Replacing all occurrences of 'ä' by auml; in the collected works of Shakespeare ; ) has a maximum memory usage of around 65MB with the current implementation of intersperse while it has a maximum memory usage of only around 5KB with the less strict implementation. No surprise, there aren't many 'ä's in Shakespeare's works, are there? I think this is due to the Wadler tuple space leak. Yup. The same would apply to the current implementation of lines. I wonder whether an implementation of lines analogous to splitBy has any disadvantages. Hardly, but yes. 'break' constructs a pair pretty immediately, so case break p (x:xs) of (pre, post) - pre : case post of [] - [] (y:ys) - stuff can only do harm if (p x) diverges, but then it does. Currently, lines (_|_ : rest) = _|_ : _|_ while withe the break, we'd have lines' (_|_ : rest) = _|_ On the other hand, the current implementation of lines does not seem to suffer from Wadler's tuple space leak (according to one test I made), so I'd stick with the current implementation for the time being. That is, we could have intersect [] _|_ = [] and intersect (_|_:_|_) [] = [] or intersect [] (_|_:_|_) = [] and intersect _|_ [] = [] and the current implementation satisfies neither. Right. So the question is, has the current implementation advantages over either of these? (I don't see any.) If not, which of these two behaviours is preferable? I'd prefer the first one as it is in line with the left to right pattern matching of Haskell. Moi aussi. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On Sep 2, 2010, at 9:10 AM, Stephen Sinclair wrote: Sorry to go a bit off topic, but I find it funny that I never really noticed you could perform less-than or greater-than comparisons on Bool values. What's the semantic reasoning behind allowing relative comparisons on booleans? In what context would you use it? The Boolean values form a Boolean lattice. That's reason enough. It seems to me a throwback to C's somewhat arbitrary assumption that False=0 and True=1. That's not arbitrary at all. 0 and 1 are very special numbers, because of the roles they play in addition and multiplication. They absorb and identify things. http://en.wikipedia.org/wiki/Boolean_algebra_(structure)___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Crypto-API is stabilizing
On Thu, Sep 2, 2010 at 3:07 PM, Sebastian Fischer
s...@informatik.uni-kiel.de wrote:
data Key = Key {
encrypt :: B.ByteString - B.ByteString,
decrypt :: B.ByteString - B.ByteString,
keyLength :: BitLength,
serialize :: B.ByteString}
rsa :: RandomGen g = BitLength - g - ((Key,Key), g)
One reason against this is simply that all the other constructs
(block/stream cipher, hashes) are classes, it would be odd for there
to be a single exception. A better reason is the data structure has
no way to implement generateKeyPair.
Why not use
generateKeypair :: MonadRandom m = BitLength - m (Maybe (p,p))
Because MonadRandom dictates mtl, and is heavier weight than a single
class. I was hoping to keep this agnostic (mtl is only required for
testing or benchmarks in crypto-api). If MR the more agreeable path
then I'll do it, though this means I use the unholy fail function.
Even if that's the case (and more people weighing in would help) I
still want to include Data.Crypto.Random and welcome comments.
Cheers,
Thomas
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Re: [Haskell-cafe] creating a type based on a string
You may also look at Data.Dynamic / Data.Typeable. It may not work really well, depending on how you defined A and B. In GHC, it should work with any type produced with the haskell 98 use of the keyword data, though. This is the canonical solution to cope with the GHC API returning values of arbitrary type. Good luck, Pierre El 02/09/2010, a las 16:31, Andrew U. Frank escribió: I have a user input (string) and need to select one of two types. depending what the input is. is this possible? data A data B data X n = X String op :: String - X n op a = X a :: X A op b = X b :: X B this does obviously not compile. is there a way to achieve that the type X A is produced when the input is a and X B when the input is b? thank you for help! andrew ___ 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] CnC Haskell
Belated update: The haskell-cnc distribution (if you grab it from darcs) now has a front-end that parses the graph description files. http://hackage.haskell.org/package/haskell-cnc For any readers who haven't seen this before -- CnC is a parallel programming model that includes both a library and a small DSL for graph specification. The specification file describes the structure of an application and captures various invariants about data access. The CnC front-end in the haskell-cnc distro is meant to replace existing CnC spec translators and generate code for all host languages that support the programming model (currently C++, Java, .NET, Haskell). Also the graph specification language is getting a refresh in the process (new features/syntax). The parser is done with Happy. What's there right now only generates C++ code, but the Haskell codegen is straightforward and should come along shortly (anyone want to help?). The purpose of such a front-end is to generate code that: (1) saves boilerplate in graph construction (more of a problem in non-haskell languages) (2) correctness: enforces invariants expressed in the specification (3) performance: generate code that embodies graph analysis and optimizations (based also on profiling data) Cheers, -Ryan On Fri, Jun 25, 2010 at 11:02 AM, David Peixotto d...@rice.edu wrote: There is a reference for the CnC grammar in the repository for the .NET implementation. http://github.com/dmpots/CnC.NET/blob/master/CnC.NET/CnC.NET/cnc.grammar The parser specification for fsyacc (the F# YACC implementation) is here: http://github.com/dmpots/CnC.NET/blob/master/CnC.NET/CnC.NET/Parser.fsy The textual representation is still in flux a bit, but this grammar should be enough of a guide for implementing a parser in Haskell. The grammar is left recursive, so using a parser generator like Happy would be a good choice. The textual representation will actually be a bit different depending on the underlying language since the types of items stored in a collection is part of the description. For example in C, an item collection that stores an array of ints would be declared like: [int* A]; but in Haskell we would want to write something like [Array Int Int A]; I think dealing with type declarations would in the textual representation would be the main difference in implementing the parser in Haskell. Once the textual representation has been parsed to an AST it should be possible to generate the Haskell code that builds the graph using the haskell-cnc package. -David On Jun 23, 2010, at 3:56 PM, Vasili I. Galchin wrote: On Wed, Jun 23, 2010 at 3:47 PM, Don Stewart d...@galois.com wrote: vigalchin: Hello, I have been reading work done at Rice University: http:// habanero.rice.edu/cnc. Some work has been done by http://www.cs.rice.edu/ ~dmp4866/ on CnC for .Net. One component that David wrote a CnC translator that translates CnC textual form to the underlying language, e.g. F#. Is anybody working on a CnC textual form translator for Haskell so a Haskell user of CnC Haskell can write in a higher level?? Ah, so by a translator from high level CnC form to this: http://hackage.haskell.org/packages/archive/haskell-cnc/latest/doc/hml/Intel-Cnc.htmlhttp://hackage.haskell.org/packages/archive/haskell-cnc/latest/doc/html/Intel-Cnc.html ^^ exactly what I mean ? Do you have a reference for the CnC textual form? ^^ if you mean something like a context-free grammatical definition of the CnC textual form ,,, the answer is I haven't seen such a reference. V. -- Don ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Crypto-API is stabilizing
Is there a reason this belongs under the Data. prefix? Why not break it out
into Crypto, so future implementers of algorithms can also put their stuff
under there. Everything at some level can be seen as Data, and it would be
nice to start moving out of the overcrowded module hierarchy.
On Fri, Sep 3, 2010 at 1:59 AM, Thomas DuBuisson thomas.dubuis...@gmail.com
wrote:
On Thu, Sep 2, 2010 at 3:07 PM, Sebastian Fischer
s...@informatik.uni-kiel.de wrote:
data Key = Key {
encrypt :: B.ByteString - B.ByteString,
decrypt :: B.ByteString - B.ByteString,
keyLength :: BitLength,
serialize :: B.ByteString}
rsa :: RandomGen g = BitLength - g - ((Key,Key), g)
One reason against this is simply that all the other constructs
(block/stream cipher, hashes) are classes, it would be odd for there
to be a single exception. A better reason is the data structure has
no way to implement generateKeyPair.
Why not use
generateKeypair :: MonadRandom m = BitLength - m (Maybe (p,p))
Because MonadRandom dictates mtl, and is heavier weight than a single
class. I was hoping to keep this agnostic (mtl is only required for
testing or benchmarks in crypto-api). If MR the more agreeable path
then I'll do it, though this means I use the unholy fail function.
Even if that's the case (and more people weighing in would help) I
still want to include Data.Crypto.Random and welcome comments.
Cheers,
Thomas
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[Haskell-cafe] On to applicative
This may be a dumb question, but here goes. Types Maybe, Either, List, are types and also instances of Functor (and Monad). Assuming (-) is also a type, where can I find its type definition? Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
On Thu, Sep 2, 2010 at 9:16 PM, michael rice nowg...@yahoo.com wrote: This may be a dumb question, but here goes. Types Maybe, Either, List, are types and also instances of Functor (and Monad). Assuming (-) is also a type, where can I find its type definition? (-) is a built-in type. You could say its definition is in the Haskell Report. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] On to applicative
Cool, I'll go looking for it. I couldn't find anything on Hoogle. Thanks, Michael --- On Thu, 9/2/10, David Menendez d...@zednenem.com wrote: From: David Menendez d...@zednenem.com Subject: Re: [Haskell-cafe] On to applicative To: michael rice nowg...@yahoo.com Cc: haskell-cafe@haskell.org Date: Thursday, September 2, 2010, 9:26 PM On Thu, Sep 2, 2010 at 9:16 PM, michael rice nowg...@yahoo.com wrote: This may be a dumb question, but here goes. Types Maybe, Either, List, are types and also instances of Functor (and Monad). Assuming (-) is also a type, where can I find its type definition? (-) is a built-in type. You could say its definition is in the Haskell Report. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
On 3 September 2010 11:57, John Millikin jmilli...@gmail.com wrote: Is there any particular reason you're using XHTML instead of HTML? [snip] XHTML is supported by most modern browsers (Firefox, Chrome, Safari, Opera, etc), but not by any currently released version of Internet Explorer. Sounds like a good enough reason to me... :p -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Unnecessarily strict implementations
On 3 September 2010 04:57, Arie Peterson ar...@xs4all.nl wrote: On Thu, 2 Sep 2010 19:30:17 +0200, Daniel Fischer daniel.is.fisc...@web.de wrote: Why would one consider using Ord for Map an abuse? A kludge, for performance reasons, but an abuse? Because it forces one to declare Ord instances for types which have no natural ordering. It is useful to *not* have such instances, in order to catch programming errors. What precisely do you mean by natural ordering? A separate type class for types which can be ordered in some (possibly arbitrary) way, for use in Data.Map, would remedy this. Sure... except that the way Data.Map and Data.Set are implemented is by a binary tree, and you typically want some kind of ordering for those. How is a type class that represents arbitrary ordering any different from what we already have? The notation might not be the best if you consider the ordering to be arbitrary, but what else would you use? isArbitrarilyBefore :: (ArbitraryOrdering a) = a - a - Bool ? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
I am well aware of the differences between HTML and XHTML. I choose to switch Haddock's output from HTML to XHTML mostly because I have found the consistency of rendering cross-browser to be greater and easier to achieve with XHTML. I'm not alone in this opinion: Many well respected web design authorities have promoted, and publish their own sites, in XHTML.[1] Even Microsoft's own developer web site uses it[2]! Indeed, there is just one kind of validation error in the pages: the ids for section headings within a page are pure numbers and need an alphabetic prefix. That said, they work just fine in all browsers. I did fix the very bad validation problems with other ids (those that link to specific program symbols), and several other classes of ids. I will push my fix for the remaining ids and it will appear in the next release.[3,4] As for extensions and doctypes, I believe that we are following best practices for the most interoperable result among browsers, and given that we need to produce output that will be served in a variety of ways including different web servers, and being browsed directly off the file system.[5] Of course, as soon as it is viable, I would love to move Haddock's output to HTML 5. However, given the pace of adoption of such standards, and the range, age and mix of browsers that readers of Haddock's output use, it is likely to be two years off. - Mark [1] See, for example: http://www.alistapart.com/ http://www.csszengarden.com/ http://www.quirksmode.org/ http://happycog.com/ http://www.w3.org/ all of which are published as XHTML [2] See: http://msdn.microsoft.com/en-us/default.aspx [3] Considerable thought was put into both making identifiers validating, while maximizing browser interoperability and forward/backward compatibility. See: http://projects.haskell.org/pipermail/haddock/2010-August/000623.html [4] Given that the prior Haddock produced pages with much more significant validation errors and they didn't seem to cause issues, I don't think we should rush a point fix just for this change. [5] I can't find any evidence for your assertion that Internet Explorer doesn't support XHTML, or the way Haddock names the files (and hence URLs). Mark Lentczner http://www.ozonehouse.com/mark/ IRC: mtnviewmark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Restricted type classes
When I released the first version of container-classes (which I hacked on during AusHac), some people said I should split out the various folding, etc. into duplicates of the current Foldable class, etc. rather than having large monolithic classes. I've been working on this (see my more recent email with the subject along the lines of fighting the type system), and I think I've worked out how to do this: * Have one version of the class (when this makes sense) for values of kind * * Have another version that's closer to the original class for kind * - * but allowing restrictions (e.g. allowing Set to be an instance of Functor). This is based upon Ganesh Sittampalam's rmonad package (http://hackage.haskell.org/package/rmonad). Rather than my original goal of forcing all kind * - * values to be instances of the kind * classes, my new approach is to write instances that automatically make all instances of a * - * class to also be an instance of the kind * class, and to use a newtype wrapper with a phantom type value to allow lifting/promotion of a kind * value to a kind * - * value (e.g. foo :: (Word8 - Word8) - ByteString - ByteString; foo f = unpromote . fmap f . Promote is a valid usage, rather than using the kind * function of rigidMap). My goal with this is that if I have duplicated a class Foo to allow restricted values, then it should be a drop-in replacement for the original in terms of _usage_ (i.e. the class and method/function names are the same, but the type signatures are not). However, I would appreciate the communities advice on a few matters: 1) How should I name the kind * versions? For example, the kind * version of Functor is currently called Mappable with a class method of rigidMap. What should I call the kind * version of Foldable and its corresponding methods? Is there a valid system I can use for these? 2) How far should I go? Should I restrict myself to the data-oriented classes such as Functor, Traversable, etc. or should I try to make restricted versions of Applicative and Monad? Assuming I should: 2a) Which namespace to use? Should Monad go in Data.Restricted.Monad to keep it in the same namespace as the other classes, or should I make it closer to base with Control.Restricted.Monad? 2b) Is it OK to promote functions that use a class to being class methods? When I was discussing this in #haskell several people mentioned that defining something like liftA2 for the Set instance of (restricted) Applicative would make more sense than the default * (since (a - b) isnt' an instance of Ord). 2c) Should I keep the classes as-is, or should I explicitly put in the constraints mentioned in the Typeclassopedia (e.g. make Applicative an explicit superclass of Monad, and define return = pure for compatability reasons)? If so, should I bring over Pointed, etc. from category-extras to round out the set or just stick with classes that are already in base? 3) Am I wasting my time with this? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: Haddock version 2.8.0
On Thu, Sep 2, 2010 at 21:14, Mark Lentczner ma...@glyphic.com wrote: I choose to switch Haddock's output from HTML to XHTML mostly because I have found the consistency of rendering cross-browser to be greater and easier to achieve with XHTML. I'm not alone in this opinion: Many well respected web design authorities have promoted, and publish their own sites, in XHTML.[1] Even Microsoft's own developer web site uses it[2]! You're not generating anything browsers will parse as XHTML, so I find it unlikely that attaching the correct doctype will cause problems. I am extremely skeptical that using an HTML4 doctype will render incorrectly when an unrecognized doctype works as expected across all browsers. [1] See, for example: http://www.alistapart.com/ http://www.csszengarden.com/ http://www.quirksmode.org/ http://happycog.com/ http://www.w3.org/ all of which are published as XHTML [2] See: http://msdn.microsoft.com/en-us/default.aspx Browsers treat any data sent using the text/html MIME-type as HTML. Those pages are being served as HTML, so browsers treat them as HTML with an unknown doctype. In particular, CSS and JS behavior on these sites will be that of HTML, *not* XHTML. Firefox will show you how the page is being rendered (HTML or XHTML) in the page info dialog. I don't know of any similar feature in Chrome. [5] I can't find any evidence for your assertion that Internet Explorer doesn't support XHTML, or the way Haddock names the files (and hence URLs). IE versions 8 and below (I've not tested IE9) will not render XHTML -- they pop up a save as dialog box. You're welcome to verify this by opening an XHTML page (such as http://ianen.org/haskell/dbus/ ) in IE. You may be confused, because the pages you mentioned earlier *are* rendering in IE. However, they are not being rendered as XHTML -- again, browsers are rendering them as HTML with an unrecognized doctype. Haddock is generating files with an .html extension, which causes webservers to serve it using text/html, the incorrect MIME-type. The correct extension for XHTML content is .xhtml. For some reason, it is common to use XHTML doctypes in HTML documents -- I assume because people think the X makes it more modern. However, this is incorrect behavior. It is better to serve a page correctly as HTML4 than incorrectly as tag soup. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
