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Re: problems installing ghc 6.6 with extralibs (bad interface file)
by Thomas Hartman 08 Mar '07

08 Mar '07

Thanks. I incorporated these changes, and it cranks longer now before failing. But still fails, now with a seg fault. Does this just mean I don't have enough ram, or cpu, or ... Any ideas? thomas. ************* thartman@linodewhyou:~/haskellInstalls$ tail -n13 out.txt ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename -istage2/typecheck -istage2/deSugar -istage2/coreSyn -istage2/specialise -istage2/simplCore -istage2/stranal -istage2/stgSyn -istage2/simplStg -istage2/codeGen -istage2/main -istage2/profiling -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten -istage2/iface -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI -DBREAKPOINT -package template-haskell -threaded -package readline -DUSE_READLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser -package unix -package Cabal -package regex-compat -ignore-package lang -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name ghc-6.6 -fgenerics -fno-cse -c main/DriverPipeline.hs -o stage2/main/DriverPipeline.o -ohi stage2/main/DriverPipeline.hi <<ghc: 489718944 bytes, 1371 GCs, 11780600/23325480 avg/max bytes residency (7 samples), 59M in use, 0.00 INIT (0.00 elapsed), 3.40 MUT (18.69 elapsed), 3.69 GC (3.91 elapsed) :ghc>> ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename -istage2/typecheck -istage2/deSugar -istage2/coreSyn -istage2/specialise -istage2/simplCore -istage2/stranal -istage2/stgSyn -istage2/simplStg -istage2/codeGen -istage2/main -istage2/profiling -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten -istage2/iface -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI -DBREAKPOINT -package template-haskell -threaded -package readline -DUSE_READLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser -package unix -package Cabal -package regex-compat -ignore-package lang -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name ghc-6.6 -fgenerics -c main/GHC.hs -o stage2/main/GHC.o -ohi stage2/main/GHC.hi gcc: Internal error: Segmentation fault (program cc1) Please submit a full bug report. See <URL:http://gcc.gnu.org/bugs.html> for instructions. For Debian GNU/Linux specific bug reporting instructions, see <URL:file:///usr/share/doc/gcc-4.0/README.Bugs>. <<ghc: 595874452 bytes, 1818 GCs, 14564135/30202688 avg/max bytes residency (8 samples), 74M in use, 0.00 INIT (0.00 elapsed), 5.10 MUT (17.37 elapsed), 5.80 GC (12.08 elapsed) :ghc>> make[1]: *** [stage2/main/GHC.o] Error 1 make: *** [install] Error 1 ~/haskellInstalls thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 | tee out.txt thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh if [ ! -f ghc-6.6-src.tar.bz2 ]; then wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 fi if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 fi tar -tvjf ghc-6.6-src.tar.bz2 tar -tvjf ghc-6.6-src-extralibs.tar.bz2 pushd ghc-6.6 (cd compat && make clean && make UseStage1=YES) (cd utils && make clean && make UseStage1=YES) ./configure make make install popd thartman@linodewhyou:~/haskellInstalls$ 2007/2/27, Thomas Hartman <tphyahoo(a)gmail.com>: > I incorporated these changes to my install script, and now it cranks > longer before failing, but still fails. Now with a seg fault. > > For some odd reason the final crash snipped below didn't get written > to out.txt, otherwise I would have attached it. > > Any ideas to get it working? > > Thanks, thomas. > > ********************************** > > thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh > if [ ! -f ghc-6.6-src.tar.bz2 ]; then > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 > fi > > if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 > fi > > > tar -tvjf ghc-6.6-src.tar.bz2 > tar -tvjf ghc-6.6-src-extralibs.tar.bz2 > pushd ghc-6.6 > (cd compat && make clean && make UseStage1=YES) > (cd utils && make clean && make UseStage1=YES) > ./configure > make > make install > popd > thartman@linodewhyou:~/haskellInstalls$ > > thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 > | tee out.txt > > .... > > ../compiler/ghc-inplace -H16m -O -istage2/utils -istage2/basicTypes > -istage2/types -istage2/hsSyn -istage2/prelude -istage2/rename - > istage2/typecheck -istage2/deSugar -istage2/coreSyn > -istage2/specialise -istage2/simplCore -istage2/stranal > -istage2/stgSyn -istage2 > /simplStg -istage2/codeGen -istage2/main -istage2/profiling > -istage2/parser -istage2/cprAnalysis -istage2/ndpFlatten > -istage2/iface > -istage2/cmm -istage2/nativeGen -istage2/ghci -Istage2 -DGHCI > -DBREAKPOINT -package template-haskell -threaded -package readline > -DUSE_R > EADLINE -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser > -package unix -package Cabal -package regex-compat -ignore-package > lang > -recomp -Rghc-timing -H16M '-#include "cutils.h"' -package-name > ghc-6.6 -fgenerics -c main/GHC.hs -o stage2/main/GHC.o -ohi > stage2 > /main/GHC.hi > gcc: Internal error: Segmentation fault (program cc1) > Please submit a full bug report. > See <URL:http://gcc.gnu.org/bugs.html> for instructions. > For Debian GNU/Linux specific bug reporting instructions, see > <URL:file:///usr/share/doc/gcc-4.0/README.Bugs>. > > <<ghc: 595874452 bytes, 1818 GCs, 14564135/30202688 avg/max bytes > residency (8 samples), 74M in use, 0.00 INIT (0.00 elapsed), 5.10 MUT > (17 > .37 elapsed), 5.80 GC (12.08 elapsed) :ghc>> > make[1]: *** [stage2/main/GHC.o] Error 1 > make: *** [install] Error 1 > ~/haskellInstalls > > > > 2007/2/27, Simon Marlow <simonmarhaskell(a)gmail.com>: > > Thomas Hartman wrote: > > > I installed ghc 6.6 from source ok. But then when I tried installing > > > it with the "extralibs" to get all the functionality that had been > > > unbundled in 6.6, I hit a glitch. > > > > > > Anyone ever seen anything like this? > > > > > > In case it matters, this is ssh-ed in to a virtualized user mode linux > > > session. > > > > > > ***************************************** > > > > > > thartman@linodewhyou:~/haskellInstalls$ cat install-ghc-6.6.sh > > > if [ ! -f ghc-6.6-src.tar.bz2 ]; then > > > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src.tar.bz2 > > > fi > > > > > > if [ ! -f ghc-6.6-src-extralibs.tar.bz2 ]; then > > > wget http://www.haskell.org/ghc/dist/6.6/ghc-6.6-src-extralibs.tar.bz2 > > > fi > > > > > > > > > tar -tvjf ghc-6.6-src.tar.bz2 > > > tar -tvjf ghc-6.6-src-extralibs.tar.bz2 > > > pushd ghc-6.6 > > > ./configure > > > make > > > make install > > > popd > > > thartman@linodewhyou:~/haskellInstalls$ sudo ./install-ghc-6.6.sh 2>&1 > > > | tee out.txt > > > thartman@linodewhyou:~/haskellInstalls$ tail -n20 out.txt > > > ------------------------------------------------------------------------ > > > make[2]: Nothing to be done for `install'. > > > ------------------------------------------------------------------------ > > > == make install - --no-print-directory -r; > > > in /home/thartman/haskellInstalls/ghc-6.6/utils/ghc-pkg > > > ------------------------------------------------------------------------ > > > Creating a symbolic link from ghc-pkg-6.6 to ghc-pkg in /usr/local/bin > > > for i in ghc-pkg-6.6; do \ > > > /usr/bin/install -c -m 755 $i /usr/local/bin; \ > > > done > > > /usr/local/bin/ghc -H16m -O -cpp -Wall -fno-warn-name-shadowing > > > -fno-warn-unused-matches -i../../compat -ignore-package Cabal > > > -Rghc-timing -c Main.hs -o Main.o -ohi Main.hi > > > > > > Main.hs:19:0: > > > Bad interface file: ../../compat/Distribution/InstalledPackageInfo.hi > > > mismatched interface file versions: expected 6060, found 6 > > > <<ghc: 24591324 bytes, 4 GCs, 106128/106128 avg/max bytes residency (1 > > > samples), 16M in use, 0.00 INIT (0.02 elapsed), 0.25 MUT (0.42 > > > elapsed), 0.10 GC (0.12 elapsed) :ghc>> > > > make[2]: *** [Main.o] Error 1 > > > make[1]: *** [install] Error 1 > > > make: *** [install] Error 1 > > > > I'm guessing what happened is that during the install the build system decided > > to rebuild ghc-pkg (I'm not sure why), but by that time you had already > > installed the new compiler, and the previous interface files weren't compatible > > with the new compiler. (I don't know why that would be the case either, since > > both compilers are 6.6...). > > > > You might be able to work around it by > > > > $ (cd compat && make clean && make UseStage1=YES) > > $ (cd utils && make clean && make UseStage1=YES) > > > > Cheers, > > Simon > > > > >

4 4

LDFLAGS
by unknown＠example.com 08 Mar '07

08 Mar '07

I have built ghc-6.6 twice for 64-bit OpenBSD 4.0 with LDFLAGS=-L/usr/local/lib set as an environmental variable. Both times the built ghc did not find -lgmp until I modified lib/ghc-6.6/package.conf by adding "-L/usr/local/lib" to ldOptions. What do I set in order to have ldOptions set properly at the conclusion of make;make install? Thanks, Dave Feustel

2 1

TVars & throw
by Thomas Conway 08 Mar '07

08 Mar '07

Hi All, Consider the following: foo = do v <- newTVar "hi there!" throwDyn v main = do catchDyn (atomically foo) \v -> do x <- atomically (readTVar v) putStr x I.e. throw information that gets rolled back from inside a transaction, catch it and use it. This looks like bad. I assume it actually works, but should it? T. -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

3 2

lhs2TeX
by Thomas Conway 08 Mar '07

08 Mar '07

Hi all, I noticed that in the polycode mode, lhs2TeX produces odd looking output for hex constants. E.g. \begin{code} wibble = 0x7F \end{code} It produces a nice little gap between the 0 and the x. Inspecting the latex source, it even goes to some effort to do so: \mathrm{0}\;\Varid{x7F} I couldn't see anything in the manual to show me how. Anyone? -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

1 0

Usage of . and $
by Jefferson Heard 08 Mar '07

08 Mar '07

Usually, I can do this, but today, my brain is weak, and I'm just trying to get this piece of code out the door. My code looks like this: weight = sum (IntMap.elems (IntMap.intersectionWith (\x y -> x*y) queryVector rationalProjection)) I know that this will work (ignoring indentation): sum $ IntMap.elems $ IntMap.intersectionWith (\x y -> x*y) queryVector rationalProjection But why won't this?: sum . IntMap.elems . IntMap.IntersectionWith ... Is there a difference between the "elegance" of function composition versus application?

10 15

MPTCs and rigid variables
by David House 08 Mar '07

08 Mar '07

class Foo a b | a -> b instance Foo Int String bar :: Foo Int b => b bar = "rargh" Is there any reason why that shouldn't work? GHC gives one of its silly "b is a rigid variable" errors (aside: that's a really confusing error; I'd prefer something like Hugs's "Infered type is not general enough"). -- -David House, dmhouse(a)gmail.com

9 16

ANN: Bugfixes for regex-posix and regex-pcre ByteString use
by Chris Kuklewicz 07 Mar '07

07 Mar '07

I got a bug report from the #haskell IRC channel last night that empty ByteStrings were broken. The new bugfixed versions of the affected packages are: regex-posix-0.92 regex-posix-0.72 regex-pcre-0.92 regex-pcre-0.81 All the above have been uploaded to http://hackage.haskell.org/ and are available via darcs (see below). Details: regex-posix-0.92 replaces the "unstable" regex-posix-0.91 that I announced yesterday. The bug fix also applied to ByteString.Lazy repository: http://darcs.haskell.org/packages/regex-unstable/regex-posix/ regex-posix-0.72 replaces the regex-posix-0.71 that came with GHC 6.6 repository: http://darcs.haskell.org/packages/regex-posix/ The repository version is setup to compile alongside GHC in some way that I cannot easily package, so the tarball on hackage has edited Wrap.hsc and cabal files. regex-pcre-0.92 replaces the "unstable" regex-pcre-0.91 that I announced yesterday. The bug fix also applied to ByteString.Lazy repository: http://darcs.haskell.org/packages/regex-unstable/regex-pcre/ regex-pcre-0.81 replaces the "stable" regex-pcre-0.80 that is compatible with the regex-base-0.71 supplied with GHC or regex-base-0.72 that I announced yesterday. repository: http://darcs.haskell.org/packages/regex-pcre/

3 3

LGPL libraries
by Alex Queiroz 07 Mar '07

07 Mar '07

Hallo, Gtk2Hs and HDBC are both LGPL licensed, but aren't they always static linked? Is there a way to use them in closed-source programs? Cheers, -- -alex http://www.ventonegro.org/

13 15

Haskell File reading
by cornmouse 07 Mar '07

07 Mar '07

I have a txt file, which contains a paragraph. I am trying to read the file, and pass the contents of the file as a string to another function called "createIndex". "createIndex" is a function to generate index of the input string. Below is my code to read the file : main :: IO () main = do putStr "Enter input file name.txt: " filename <- getLine content <- readFile filename createIndex content createIndex :: String -> [ ([Int], String) ] createIndex {- contents of the function... -} I am using Hugs compiler, when i execute, i got an error Type error in generator *** Term : showString content *** Type : [Char] -> [Char] *** Does not match : IO a IO> I know the data type doesn't match. How do i go about this?

4 3

Re: [Haskell] Haddock not being able to read interface file
by Simon Marlow 07 Mar '07

07 Mar '07

Wolfgang Jeltsch wrote: > Am Dienstag, 6. März 2007 12:09 schrieben Sie: >> Wolfgang Jeltsch wrote: >> […] > >>> However, Haddock outputs the following: >>> >>> haddock: Warning: The interface file "base.haddock" could not be >>> read. Maybe it's from a later version of Haddock? >>> >>> This happens with Haddock 0.8 as well as the current development version >>> of Haddock. >> It's possible the interface files are not portable between 32 and 64-bit >> machines, and you're using one generated for a different word size. I >> haven't verified this, but I'll make a note to check for the next version >> of Haddock. I imagine we'll move to using Data.Binary anyway, which should >> fix any non-portability issues. > > Hello Simon, > > I use a 64 bit machine. Was base.haddock on the Haskell website created on a > 32 bit machine? I don't honestly know, it could have been either. Cheers, Simon

1 0

Haskell Cookbook?
by Alexy Khrabrov 07 Mar '07

07 Mar '07

So I'm picking up Haskell bit by bit, and I found the code examples transpiring here most useful. Reflecting why it's harder to pick up Haskell than say Ruby or Python, here's what I found -- those languages deal with a typical domain available to any programmer -- his own computer/system/shell. The artifacts are files, directories, timestamps, etc. The stuff every programmer understands in their sleep. APIs. So I loved the shell-script beautification thread. That's how I learn about new modules and their functions -- as use cases. I also found some pieces of Haskell strewn around people's websites, blogs, forums; even at paste.lisp.org. I'm gathering them for my own purpose and trying to compile and run them. Wouldn't it be nice -- in case it doesn't exist already -- a[n O'Reilly[-like]] Haskell Cookbook? That would be the best way to learn Haskell. I've found a wikibook on Haskell, but I look for a big bag of small, self-contained programs. Perhaps you esteemed veterans can dig your small scripts and paste them into a wiki? Examples needed -- how to connect to a database; to a web service (e.g. Amazon); read a csv file; represent data equivalent to a directory listing; a text file/XML; etc... Cheers, Alexy

8 10

Programming performance
by Tim Newsham 07 Mar '07

07 Mar '07

I'm interested in understanding how fast people can program small utility and experiment type programs in haskell. I'm also interested in seeing what types of solutions people who are experienced and code quickly end up with. Towards this end I set up a small informal experiment on the wiki: http://www.haskell.org/haskellwiki/Programming_performance Hopefully the problem is small, fun and easy without being too unrealistic. and a question about the wiki/page: is there a simple way to host the input data on the wiki? Tim Newsham http://www.thenewsh.com/~newsham/

2 1

weak references and sharing
by Thomas Conway 07 Mar '07

07 Mar '07

Hi All, I have the situation where I have something like the following: type Foo = TVar Int data Clasp t = Clasp t makeClasp x f = do let c = Clasp x mkWeakRef c (Just (f x)) return c finis p = do atomically $ do x <- readTVar p writeTVar p (x - 1) .... makeClasp p finis .... The Foo object has a greater lifetime than the Clasp. The bit I want you to focus on is the three lines: let c = Clasp x mkWeakRef c (Just (f x)) return c We can only be sure that (f x) will be called after we let go of the returned value if we can be sure that the language implementation preserves the (explicit) sharing of 'c' between the call to mkWeakRef and return. In particular, if the implementation rewrote the fragment as: mkWeakRef (Clasp x) (Just (f x)) return (Clasp x) then the finalizer might be called sooner than we expect. The problem is, that as I read it, making a distinction between the two fragments would be a violation of referential transparency. So here's the question: is there a way of writing this that is guaranteed to work on all correct implementations of Haskell? cheers, T. ps FWIW, the actual situation is that we have a TVar pointing to a record representing a 'page' of an external data structure. For some operations we need to make sure the the page is in-memory, but when all the operations using a particular page are finished, we'd like to flush it back to disk if it has been modified. Now it'd be really nice to use the garbage collector to tell us when noone is using the in-memory version of the page, so we can write it out. However, if we can't be certain that we've got a genuine hard-reference to the object, then we can't be sure it will not be prematurely flushed. -- Dr Thomas Conway You are beautiful; but learn to work, drtomc(a)gmail.com for you cannot eat your beauty. -- Congo proverb

1 0

IO and lazyness.
by D.V. 07 Mar '07

07 Mar '07

Hello, I'm still learning Haskell and I am stuck on a probably simple problem. Assume I have a file where lines are of the form "key=value" I want to search a value in that file and came up with the following code. > rechf :: String -> IO (Maybe String) > rechf r = bracket (openFile "liste" ReadMode) (hClose) (rechf2 r) > > rechf2 :: String -> Handle -> IO (Maybe String) > rechf2 r h= do > f <- hGetContents h > --print f > return $ rech r $ lines f > > rech :: String -> [ String ] -> Maybe String > rech r l = lookup r $ map span2 l > > span2 :: String->(String,String) > span2 c = (a,b) > where a=takeWhile (/='=') c > b=drop 1 $ dropWhile (/='=') c Now the problem is this : 1) if I try rechf, it returns nothing even for a key that exists in the file. 2) if I uncomment the line where there is "print f", the key is found and the value returned. I'm guessing print forces f to be evaluated, so the file is actually read, but I was wondering why it doesn't work without it and how to correct that. David.

8 11

Literate haskell format unclear (implementation and specification inconsistencies)
by Isaac Dupree 07 Mar '07

07 Mar '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Trying to implement literate haskell[*], I realized several ways in which the correct behavior for unliterating (especially with regard to errors) was unclear. I have several cases which ghc, hugs and Haskell 98 have differing opinions on! The Report as it stands is far from a clear and complete specification (and I didn't find anything in the Haskell' wiki/trac about literate haskell). [*](particularly, to make DrIFT able to deal with TeX-style lhs - there's unfinished work in darcs repo http://isaac.cedarswampstudios.org/2007/DrIFT/ ) testing with: ghc: 6.4.2, 6.6(some) hugs: Hugs Version 20050308 nhc98: recent darcs (1.19) report: Haskell 98 (The Revised Report: December 2002), section 9.4, http://www.haskell.org/onlinereport/syntax-iso.html#sect9.4 A full set of .lhs test files for all the issues: darcs get http://isaac.cedarswampstudios.org/2007/LiterateHaskellTests or download http://isaac.cedarswampstudios.org/2007/LiterateHaskellTests-1.tar.gz or you can try just prefixing all examples with \begin{code} module Main where main = print str \end{code} or >module Main where > main = print str as appropriate... (please don't get mangled by mail programs, initial '>'s... ): 1.[UnmatchedBegin] If a \begin{code} starts a section of code, is \end{code} _required_ before the end of the file? report: unclear ghc: required hugs, nhc98: not required The report says "entirely enclosed between", but goes on to say "More precisely:" and give a description that is not at all precise in the matter of this question. 2.[AfterBeginOrEnd/{BeginWhite,EndWhite,BeginPrint,EndPrint}] Can a line beginning \begin{code} or \end{code} have additional stuff on the end, where the directive is understood and the additional stuff is ignored? report:[yes] hugs:[yesIffAdditionalStuffIsInvisible] ghc:[case beginningOfLine of "\end{code}" -> yes "\begin{code}" -> yesIffAdditionalStuffIsInvisible] nhc98:[UNLIT_IGNORED] where yesIffAdditionalStuffIsInvisible = if (all isSpace additionalStuff) then yes else UNLIT_IGNORED UNLIT_IGNORED means that if it was inside a code block then the line is treated as program text (so it's probably a syntax error) and if it was in a literate comment section it is treated as a non-empty literate comment line. Note that it takes a careful reading of the report: for begin, program code only begins on the _following_ line. Most seem to agree that it shouldn't mess up your program to have trailing whitespace on such a line (but at least nhc98 doesn't currently implement this). Is there any reason to allow NON-whitespace in that location? 3.[IgnoringStringLiterals/{A,B}] what does "(ignoring string literals, of course)" mean? that the following(A) makes str = "string gap:end{code}" and an unended code block(A), or that it makes an ended code block(B)? (A)--------- \begin{code} str = "string gap:\ \end{code}" - --------- report:unclear, hugs:A, ghc:B, nhc98:A This works for ghc, the result being "string gap:string gap ends": (B)--------- \begin{code} str = "string gap:\ \end{code}" \begin{code} \string gap ends" \end{code} - ----------- Note that behavior 1 requires a detailed knowledge of Haskell's syntax in order to unliterate a file, for a dubious benefit (if a string literal with string gaps is used like that, the programmer could just indent the second line!) 4.[ExtraBeginEnd/{ExtraBegin,ExtraEnd}] What happens if \begin{code} appears after another \begin{code} before an \end{code}; and what happens if an \end{code} appears without a code block previously having been started by a \begin{code}? stray end: ghc, nhc98:[UNLIT_IGNORED (-> probable successful compile)] hugs:[error "\end{code} encountered outside code block"] stray begin: ghc, nhc98:[UNLIT_IGNORED (-> probable syntax error)] hugs:[error "\begin{code} encountered inside code block"] 5.[LexicalUnitAcrossLiterateComment/{StringGap,BlockComment}] Can lexical units jump across literate comment gaps? report, ghc, hugs, nhc98: yes... Note that the Report specifies it by removing all non-program lines, rather than converting them to blank lines, but an additional blank line in the middle of a Haskell program NEVER makes a difference (except for line numbering, of course). - ---------- > str = "string gap:\ This might be a literate comment. > \ends here" - --------- ghc, hugs, nhc98: "string gap:ends here" or - -------- > str = "string" > {- a comment This might be a literate comment -} with weird character sequences. > ends here -} - ---------- ghc, hugs, nhc98: think it's a fine comment I mention this because allowing these makes it complicated to preserve literate comments in a translation to .hs, because, other than cases like these, prefixing literate comment lines with "-- " works fine.[*] However, banning these could make processing that wants to report errors end up more complicated. Maybe the report could/should say that it is "not advisable", as it does for mixing '>' and {code} styles? (Also it's confusing to the programmer - I wondered "can I (and should I) really do that?!" sometimes..) [*]Haddock style is a nuisance too, which is why there are two spaces added -- Haddock seems not to recognize such comments then, as desired. Or would it be better to take the other approach and say those should count as haddock comments? 6.[TeXBirdtrack/] I understand that "It is not advisable to mix these two styles in the same file." and the report doesn't even talk about how they mix, but now that I've gotten started on the implementation inconsistencies... Actually, despite the Report's advice against it, there seems to be a consensus on what the meaning of mixing the two styles is, which I'll describe below: Sensibly, ghc, hugs and nhc98 treat begin/end{code} lines as blank for the purposes of '>'-style comment checking (which is that a code and a non-blank literate comment line can't be adjacent); this works: [TeXBirdtrack/NoLayout]------------ >module Main where >{main = print str \begin{code} ;str = "string"} \end{code} ok - ------------ Note I didn't rely on the layout rule. This should work: [TeXBirdtrack/AlignedLayout]------------ >module Main where > main = print str \begin{code} str = "string" \end{code} ok - ------------ It does in hugs and nhc98, and according to http://hackage.haskell.org/trac/ghc/ticket/210 it does in GHC HEAD now (6.7) as well. As another example, this doesn't work, for the same reason that you can't start a line with '>' in a .hs file: [TeXBirdtrack/Wrong]------------ >module Main where > main = print str \begin{code} > str = "string" \end{code} ok - ------------ Hoping to start some discussion, Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFF5gaoHgcxvIWYTTURAoF4AJwIjQ3hJ9jpwUgHiYgTB7IhN2so4QCdGCKU 96q4YIeakWtlBKOdAiFM+vU= =qzCQ -----END PGP SIGNATURE-----

5 8

Pls help about stupid question!
by iliali16 07 Mar '07

07 Mar '07

Hi folks I have this funciton to implement : leftJustified Now this function shoud justify the text acording to the number of characters per line.So for example I u put the following leftJustified :: Integer -> String -> String leftJustified n xs | acctually my problem is that I have for example the following string Hi my name is X. And what I want is to leftJustified it by 3 characters and I have to do it whithout choping words and I have to do it on the next line and what I came up is very stupid becouse it doesn't work at all like what I need but atleast it shows the string eventhough it counts not the characters but the words. leftJustified :: Integer -> String -> String leftJustified 0 xs = [] leftJustified _ [] = [] leftJustified n xs |lList (words xs) <= n = xs |otherwise = x : \n (leftJustified xs) This doesnt work but if I delete the last line it owrks as shown above. Please help me to understand how this should be done. -- View this message in context: http://www.nabble.com/Pls-help-about-stupid-question%21-tf3357906.html#a933… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

1 0

Recursion
by unknown＠example.com 07 Mar '07

07 Mar '07

Does the following code increase the level of recursion once for each input line or is the recursive construct converted to an iteration? Thanks, Dave Feustel main :: IO () main = do line <- getLine processIt line main processIt :: String -> IO () processIt s = do print (length s)

4 3

StaticDTD - Type safe markup combinator libraries from DTDs
by mm 07 Mar '07

07 Mar '07

Hello, I would like to inform you that i am currently working on a tool that transforms a Document Type Definition to a library. The resulting library contains combinators that assure proper nesting of elements to some extend. I am planning to add more constraints, that will also take care of the order of occurence of children (content model). The parsing of the DTD is done with HaXml's DTD parser. The whole thing is very much inspired by HList, HaXml, WASH/HTML and HSXML. The darcs repo is at: http://m13s07.vlinux.de/darcs/StaticDTD/ Marcel Manthe -- No one wins It's a war of man.

1 0

Pulling a monad out of a functor
by Bryan Burgers 06 Mar '07

06 Mar '07

Haskellers, Recently, I have come across a couple of situations in which I need to "pull a monad out of a functor" so to speak. The first time it was needed, I didn't think much of it, but the second time started me thinking whether there is already an existing construct for this. The type signatures I have in mind are: pull :: (Monad m, Functor f) => f (m a) -> m (f a) fmapM :: (Monad m, Functor f) => (a -> m b) -> f a -> m (f b) fmapM f = pull . fmap f You may notice that these are already defined for the List functor as 'sequence' and 'mapM'. It seems to me that if this were a class, the implementor would be defining a traversing order by defining pull; in the list case this traversing sequence is clearly defined as head to tail. I am wondering if there is already a construct for this that I am not aware of (a class, a way to defined it using monads and functors that I am not aware of, an idiom)? Is this something that frequently happens for others, or is it a sign a few of my designs have been flawed recently? Bryan

2 2

haskell zlib on win32
by Tim Newsham 06 Mar '07

06 Mar '07

Building haskell's zlib library for win32 is not trivial since it relies on an external C library. Most of the required tools are shipped with the ghc binary distribution though. I finally bit the bullet and jumped through the build hoops to install it. My notes are attached below. The build could be nicer if it was more cabalized -- ie. have the cabal file directly reference the zlib-1.2.3 sources and headers.. Problems are possible reliance on particular versions, duplicating already installed code (although in this case its pretty small), and possibly figuring out how to perform the "configuration" process without a shell.... Any opinions on this approach? --- WIN32 BUILD INSTRUCTIONS ---- I built from cygwin. Probably a little easier if you have mingwin installed. I have ghc-6.6 installed in /c/ghc/ghc-6.6 (/c is a mount point for c:\ "mount c:\\ /c"). Fetch sources $ darcs get http://haskell.org/~duncan/zlib $ cd zlib $ wget http://www.zlib.net/zlib-1.2.3.tar.gz $ tar -xzf zlib-1.2.3.tar.gz Prefer ghc's gcc (mingwin) rather than cygwins. $ export PATH=/c/ghc/ghc-6.6:/c/ghc/ghc-6.6/bin:$PATH Build zlib C code $ ./configure --prefix=/c/ghc/ghc-6.6 --libdir=/c/ghc/ghc-6.6 $ make install build haskell zlib $ cd .. $ runhaskell Setup.py configure $ runhaskell Setup.hs build $ runhaskell Setup.hs install Tim Newsham http://www.thenewsh.com/~newsham/

2 1

Lambdabot on Windows?
by Iain Alexander 06 Mar '07

06 Mar '07

Does anyone know of a standalone version of lambdabot which will run on Windows? (When I try to configure lambdabot-4.0, I get Setup.hs: cannot satisfy dependency unix-any.) -- Iain Alexander ia(a)stryx.demon.co.uk

4 4

Haskell sequence hosting
by John Goerzen 06 Mar '07

06 Mar '07

Hi everyone, I've been hosting sequence.complete.org on my own server for awhile, but have found that I haven't had time to maintain it lately. I'm looking for someone else that might be willing/able to host and maintain it. It's using Drupal on MySQL, though a fairly old version of Drupal at the moment. -- John

1 0

ANN: New release of regex packages
by Chris Kuklewicz 05 Mar '07

05 Mar '07

I would like to announce new versions of the regex-* packages. This announcement covers: Version Package Description 0.83 regex-base -- Type Classes and generic instances 0.90 regex-compat -- Uses regex-posix to provide old API 0.91 regex-dfa -- backend, pure haskell, no submatch capture 0.90 regex-parsec -- backend, pure haskell 0.91 regex-pcre -- backend, links against libpcre 0.91 regex-posix -- backend, links against standard c library 0.92 regex-tdfa -- backend, pure haskell (Posix semantics) 0.91 regex-tre -- backend, links against libtre (currently buggy) These all compile, install, and run a few test correctly. Most notably, I consider regex-tdfa to be of useful quality now. Summary of changes and recommendations: * all packages: ** import Text.Regex.XXX exposes (getVersion_Text_Regex_XXX :: Data.Version) which allows programs to access the current version number of the package ** LICENSE file provided (all are 3 clause BSD except regex-dfa is LGPL) * regex-base: ** BUGFIX: one of the RegexContext instances used tail unsafely ** RegexMaker now has makeRegexM and makeRegexOptsM for better error handling ** Extract has new instances for (Seq Char) and (ByteString.Lazy), as well as the previous [Char] and ByteString instances * all backends: ** Now support [Char], (Seq Char), ByteString, and ByteString.Lazy ** CHANGE: The (=~~) monadic match operators now use makeRegexM and will call 'fail' when a regular expression cannot be parsed. ** CHANGE: (import Text.Regex.BACKEND) now re-exports (module Text.Regex.Base) * regex-dfa: ** BUGFIX: No longer hangs on repeated nullable subpatterns * regex-tdfa: ** New backend in pure haskell that provides true Posix semantics ** Runs with excellent memory usage ** I recommend this backend for Posix extended regular expressions (leftmost longest). * regex-compat: No other changes, still uses regex-posix underneath, not recommended * regex-parsec: No other changes, I recommend regex-tdfa or regex-pcre instead * regex-pcre: No other changes, best provider of Perl's left-biased regular expressions * regex-posix: No other changes, very slow (on OS X the underlying C library is buggy) * regex-tre: No other changes, underlying libtre version 0.7.5 is still buggy Dependencies: All of the above packages have been updated to depend on regex-base>=0.80. I have only tested with GHC 6.6 on Mac OS X 10.4.8 (PPC, 32bit). Porting the backends to other Haskell compilers should be possible, though they may not support the polymorphic type class API that regex-base provides. Porting to GHC 6.4 should work once the support for (Seq Char) and ByteString[.Lazy] has been edited or externally obtained. I think only regex-tdfa actually uses bang patterns at the moment, and those could also be removed when porting. Where to get more information and the packages themselves: There is a slowly developing wiki page at http://haskell.org/haskellwiki/Regular_expressions for holding more documentation relating to these packages. I have uploaded tar.gz sources for each of the packages to hackage: http://hackage.haskell.org/packages/hackage.html They are listed under the "Text" Category: http://hackage.haskell.org/packages/archive/pkg-list.html#cat:Text Development and bug fixes continue in the darcs repositories under http://darcs.haskell.org/packages/regex-unstable/ To checkout one of the above versions with darcs you can use commands like darcs get --partial --tag=0.83 regex-base where the --tag=0.83 may be omitted to get the latest unstable version To install the packages once you have the source: For regex-pcre and regex-tre (and perhaps regex-posix) you might need to edit the end of cabal file to provide Include and Lib directories to the corresponding C library. # Compile Setup.hs for better startup speed ghc --make Setup.hs -o setup # I use my own path and "--user" .I recommend doing this to avoid overwriting # the global regex-* from GHC 6.6 ./setup configure --enable-library-profiling --prefix=YOUR_PATH --user ./setup build ./setup install Producing haddock documentation may not work and may not be up to date, with the important exception of regex-base. Future Plans: * regex-base: add support for generalized indices instead of the current Int * regex-tdfa: Improve DFA algorithm and further limit memory allocation. Try to improve performance of ByteString.Lazy matching. Cheers, Chris Kuklewicz

1 0

Tricks for making low level haskell hacking easier
by dons＠cse.unsw.edu.au 05 Mar '07

05 Mar '07

For those of you who like your Haskell code fast, then, if you're like me, reading Core output all day can give you headaches. Here's a couple of tricks I use to make optimising low level stuff easier. 1) Use Hscolour to pretty-ifiy the Core so its more parsable: ghc -O Foo.hs -ddump-simpl | HsColour -tty | less -r will colourise the Core, and pipe it into less (which will display the metachars). A screenshot: http://www.cse.unsw.edu.au/~dons/tmp/screen-core.png 2) Use vimdiff on asm output, checking the results for different ghc / gcc flags. Yes, sometimes you get down to the asm level, and it can make all the difference. It is useful when writing (*cough*) entries for the great language shootout, to compare the asm output. Currently I do this by compiling a program with different flags, or slightly different code, with -keep-tmp-files -no-recomp set, and then vimdiff the resulting asm files: http://www.cse.unsw.edu.au/~dons/tmp/asm-diff.png (before on the left, after generating pentium4 instructions on the right). Do people have any other tricks for making the tweaking of low level ghc output easier (that we should incorporate into vim/emacs support)? -- Don

3 3

Haskell 6.6 problem
by Dave Feustel 05 Mar '07

05 Mar '07

make and make install of ghc 6.6 completed successfully, but exe generated by ghc fails to load. ===test.hs=== main :: IO() main = putStr "This is a test\n" ============= ghc test.hs compilation IS NOT required /usr/bin/ld: cannot find -lgmp collect2: ld returned 1 exit status Is there a simple way to fix this? Thanks.

3 2

Haskell Weekly News: March 05, 2007
by dons＠cse.unsw.edu.au 05 Mar '07

05 Mar '07

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20070305 Issue 58 - March 05, 2007 --------------------------------------------------------------------------- Welcome to issue 58 of HWN, a weekly newsletter covering developments in the [1]Haskell community. 1. http://haskell.org/ Announcements New Book - Programming in Haskell. Graham Hutton [2]announced a new Haskell textbook: [3]Programming in Haskell. This introduction is ideal for beginner programmers: it requires no previous programming experience and all concepts are explained from first principles via carefully chosen examples. Each chapter includes exercises that range from the straightforward to extended projects, plus suggestions for further reading on more advanced topics. The presentation is clear and simple, and benefits from having been refined and class-tested over several years. 2. http://article.gmane.org/gmane.comp.lang.haskell.general/14849 3. http://www.cs.nott.ac.uk/~gmh/book.html Gtk2Hs version 0.9.11. Duncan Coutts [4]announced Gtk2Hs - a GUI Library for Haskell based on Gtk+, version 0.9.11, is [5]now available. Gtk2Hs features: automatic memory management; Unicode support; nearly full coverage of Gtk+ 2.8 API; support for several additional Gtk+/Gnome modules (Glade visual GUI builder, cairo vector graphics, SVG rendering, OpenGL extension and more). 4. http://article.gmane.org/gmane.comp.lang.haskell.general/14934 5. http://haskell.org/gtk2hs/download/ cabal-make version 0.1. Conal Elliott [6]announced Cabal-make, a GNU make include file to be used with Cabal in creating and sharing Haskell packages. A few highlights: web-based, cross-package links in Haddock docs; syntax coloring via hscolour, with per-project CSS; links from the Haddock docs to hscolour'd code and to wiki-based user comment pages. [7]It is available here. 6. http://article.gmane.org/gmane.comp.lang.haskell.general/14891 7. http://haskell.org/haskellwiki/Cabal-make Vty 3.0.0. Stefan O'Rear [8]announced a new major of [9]vty, featuring improved performance. vty is notably used in yi to provide a terminal interface supporting syntax highlighting. 8. http://article.gmane.org/gmane.comp.lang.haskell.general/14876 9. http://members.cox.net/stefanor/vty/dist/doc/html/index.html Haskell Xcode Plugin. Lyndon Tremblay [10]announced the first release of [11]a plugin for Xcode enabling Haskell syntax highlighting, Xcode projects compiling and linking, and a couple missing features, for Haskell (GHC). 10. http://article.gmane.org/gmane.comp.lang.haskell.general/14875 11. http://www.hoovy.org/HaskellXcodePlugin/ urlcheck 0.1: parallel link checker. Don Stewart [12]announced the first release of [13]urlcheck, an parallel link checker, written in Haskell. Frustrated with the resources and time consumed by 'linkchecker', urlcheck is a lightweight, smp-capable replacement in Haskell. urlcheck pings urls found in the input file, checking they aren't 404s. It uses Haskell threads to run queries concurrently, and can transparently utilise multiple cores if you have them. 12. http://article.gmane.org/gmane.comp.lang.haskell.general/14863 13. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/urlcheck-0.1 The Monad.Reader: call for copy. Wouter Swierstra [14]welcomed articles for the next issue of The Monad.Reader. Submit articles for the next issue by e-mail before April 13th, 2007. Articles should be written according to the guidelines available from [15]The Monad Reader home. 14. http://article.gmane.org/gmane.comp.lang.haskell.general/14870 15. http://www.haskell.org/haskellwiki/TheMonadReader TV-0.2 and GuiTV-0.2. Conal Elliott [16]announced TV, a library for composing tangible values ('TVs'), values that carry along external interfaces. In particular, TVs can be composed to create new TVs, and they can be directly executed with various kinds of interfaces. Values and interfaces are combined for direct use, and separable for composition. GuiTV adds graphical user interfaces to the TV (tangible value) framework, using Phooey. The functionality was part of TV up to version 0.1.1, and is now moved out to a new package to eliminate the dependency of core TV on Phooey and hence on wxHaskell, as the latter can be difficult to install. 16. http://article.gmane.org/gmane.comp.lang.haskell.general/14862 Haskell-mode 2.2. Stefan Monnier [17]released version 2.2 of [18]the Haskell-mode package for Emacs. It has very few visible changes, mostly some commands to query an underlying interactive hugs/ghci in order to get type/info about specific identifiers. 17. http://article.gmane.org/gmane.comp.lang.haskell.general/14857 18. http://www.iro.umontreal.ca/~monnier/elisp/ Data.CompactString 0.1. Twan van Laarhoven [19]announced a beta [20]Unicode version of Data.ByteString. The library uses a variable length encoding (1 to 3 bytes) of Chars into Word8s, which are then stored in a ByteString. 19. http://thread.gmane.org/gmane.comp.lang.haskell.general/14834 20. http://twan.home.fmf.nl/compact-string/ HSXML version 1.13. Oleg Kiselyov [21]announced version 1.13 of [22]HSXML. HSXML is a library for writing and transforming typed semi-structured data in Haskell -- in S-expression syntax, with the extensible set of `tags', and statically enforced content model restrictions. A particular application is writing web pages in Haskell. We obtain HTML, XHTML or other output formats by running the Haskell web page in an appropriate rendering monad. The benefit of representing XML-like documents as a typed data structure/Haskell code is static rejection of bad documents -- not only those with undeclared tags but also those where elements appear in wrong contexts. 21. http://thread.gmane.org/gmane.comp.lang.haskell.general/14835 22. http://pobox.com/~oleg/ftp/Scheme/xml.html#typed-SXML Haskell XML Toolbox 7.1. Uwe Schmidt [23]announced a new version of [24]the Haskell XML Toolbox. The main change is the step from cvs to darcs. The documentation has source links into [25]the darcs repository. [26]A tutorial is available in the Haskell wiki. 23. http://article.gmane.org/gmane.comp.lang.haskell.general/14831 24. http://www.fh-wedel.de/~si/HXmlToolbox/index.html 25. http://darcs.fh-wedel.de/hxt 26. http://www.haskell.org/haskellwiki/HXT OmegaGB, Haskell Game Boy Emulator. Bit Connor [27]announced OmegaGB, an emulator for the Nintendo Game Boy, written in pure Haskell. It uses gtk2hs for the user interface, but there is also a version that doesn't require gtk2hs and uses ascii art. You can find more information about the program at [28]the website. 27. http://article.gmane.org/gmane.comp.lang.haskell.general/14938 28. http://www.mutantlemon.com/omegagb/ Takusen 0.6. Oleg and Alistair [29]announced a new release of [30]Takusen, the database library for Haskell. There are a large number of changes and bug-fixes in this release, including improved Oracle and PostgreSQL support. 29. http://article.gmane.org/gmane.comp.lang.haskell.libraries/6209/ 30. http://darcs.haskell.org/takusen hoogle.el. David House [31]announced Hoogle.el, a simple Emacs Lisp library that nicely integrates [32]Hoogle into Emacs. 31. http://article.gmane.org/gmane.comp.lang.haskell.general/14944 32. http://haskell.org/haskellwiki/Hoogle.el Buggy nofib. Josep Silva Galiana [33]announced a 'buggy' version of the nofib collection of Haskell programs. [34]All programs contain one of these bugs: a bug that produces an incorrect result; a bug that produces non-termination; a bug that produces an exception (e.g., div by zero). [35]The buggy nofib suite can be used to test debugging tools. 33. http://article.gmane.org/gmane.comp.lang.haskell.general/14825 34. http://einstein.dsic.upv.es/darcs/nofib 35. http://einstein.dsic.upv.es/nofib nobench: Haskell implementation shootout. Don Stewart [36]announced nobench, a cross-implementation performance benchmark suite, based on nofib, [37]comparing the performance of various Haskell compilers and bytecode interpreters on a range of programs. 36. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19684 37. http://www.cse.unsw.edu.au/~dons/nobench.html Derangement version 0.1.0. Dennis Griffith [38]announced the initial version of derangement, a library for finding a derangement of a set. A derangement of a set is a permutation with no fixed points, like many constrained matching problems it is susceptible to solution via a Max-flow algorithm. 38. http://article.gmane.org/gmane.comp.lang.haskell.cafe/19714 HSH 1.0.0. John Goerzen [39]announced the first release of HSH. HSH is designed to let you mix and match shell expressions with Haskell programs. With HSH, it is possible to easily run shell commands, capture their output or provide their input, and pipe them to/from other shell commands and arbitrary Haskell functions at will. HSH makes it easy to run shell commands. But its real power is in piping. You can pipe -- arbitrarily -- between external programs, pure Haskell functions, and Haskell IO functions 39. http://article.gmane.org/gmane.comp.lang.haskell.cafe/20053 A new Haskell cookbook. Martin Bishop [40]began a preliminary page, and fleshed out some of the headers/sub-headers on the wiki page for a good Haskell Cookbook (not a PLEAC clone). [41]Please contribute. 40. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19790 41. http://haskell.org/haskellwiki/Cookbook Haskell' This section covers the [42]Haskell' standardisation process. * [43]Global variables * [44]Polymorphic components, so far * [45]do-and-if-then-else modification * [46]Fixity resolution, possible specification * [47]Disjunctive tuples 42. http://hackage.haskell.org/trac/haskell-prime 43. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2054 44. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2076 45. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2120 46. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2121 47. http://thread.gmane.org/gmane.comp.lang.haskell.prime/2133 Libraries This week's proposals and extensions to the [48]standard libraries. * [49]Data.Proxy * [50]Add extra readline completion functionality * [51]Control.Monad.Cont documentation * [52]Add First and Last wrappers around Maybe to Data.Monoid * [53]Add ioeGetLocation, ioeSetLocation to System/IO/Error.hs 48. http://haskell.org/haskellwiki/Library_submissions 49. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6238 50. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6256 51. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6287 52. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6319 53. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/6320 Discussion Haskell with only one typeclass. Oleg Kiselyov [54]described how, if the ability to define typeclasses is removed from Haskell, no expressivity is lost. If Haskell had only one, pre-defined typeclass with only one method, we could still do normal Haskell programming with standard and user-defined overloaded numerical functions, monads, monad transformers, etc. Haskell with only one typeclass can express all of Haskell98 typeclass programming idioms including constructor classes, plus multi-parameter type classes and some functional dependencies. 54. http://article.gmane.org/gmane.comp.lang.haskell.general/14936 Data type declarations are implicitly moduled. Chris Moline [55]proposed an idea to allow multiple data declarations to share constructors by having them be implicitly declared inside a module. 55. http://article.gmane.org/gmane.comp.lang.haskell.general/14847 Importance of MonadRandom. Yitzchak Gale [56]pointed out the importance of Cale Gibbard's [57]MonadRandom. This monad makes it possible to write functions that use randomness without having to specify in advance whether the source of randomness will be a pure pseudorandom number generator, as in System.Random, or physical randomness via the IO monad, such as your operating system's source of physical randomness, or random.org, or a hardware random generator. 56. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19058 57. http://www.haskell.org/haskellwiki/New_monads/MonadRandom Become a GHC build slave!. Simon Marlow [58]pointed out that, thanks largely to Ian Lynagh, GHC now has a BuildBot infrastructure to automate nightly builds on multiple platforms. This replaces the old set of shell scripts that we used to run nightly builds; now adding new clients to the setup is [59]relatively easy. So far we have various Windows builds running, and I'll be moving over the existing Linux nightly builds in due course. 58. http://article.gmane.org/gmane.comp.lang.haskell.cafe/19103 59. http://hackage.haskell.org/trac/ghc/wiki/BuildBot Editor support for low level hacking. Don Stewart [60]mentioned some tools used for making low level optimisation of GHC Haskell code easier 60. http://article.gmane.org/gmane.comp.lang.haskell.cafe/19348 Optimisation fun. Creighton Hogg [61]sparked a long thread on optimising prime sieves in Haskell 61. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19380 OO Design in Haskell Example. Steve Downey [62]began a thread on OO design in Haskell 62. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19897 Safe lists with GADTs. Neil Mitchell [63]explored a safe version of head and tail, on a safe version of lists, using GADTs 63. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/19901 Jobs Research position at Nokia Research Center. Jamey Hicks [64]announced the availability of a senior research engineer position at Nokia Research Center Cambridge, US. They are seeking an exceptional, highly motivated individual who is interested in a unique opportunity to collaborate with a world-class academic research community. This position is for the Armo project at NRC Cambridge, using Bluespec hardware description language to radically improve Nokia's ability to develop advanced SOCs and corresponding software for future mobile phones and mobile computers. We are investigating co-development of hardware and software components for such devices. Success in the project will lead to both academic publication as well as a significant positive impact on Nokia products and engineering. 64. http://article.gmane.org/gmane.comp.lang.haskell.general/14901 New PhD Positions Computing Science, Chalmers University. Koen Claessen [65]announced new [66]PhD positions for 2007, at Chalmers University of Technology. The focus is on algorithms, bioinformatics, distributed systems and computing, functional programming, formal methods, interaction design, language technology, language based security, parallel and high performance computing, programming logic and type theory, but research is not restricted to these topics. 65. http://article.gmane.org/gmane.comp.lang.haskell.general/14900 66. http://chalmersnyheter.chalmers.se/chalmers03/english/eng_vacanciesarticle.… Positions at Oxford: refactoring tools. Oege.de.Moor [67]announced the availability of positions in the Programming Tools Group at Oxford, researching aspect refactoring tools 67. http://article.gmane.org/gmane.comp.lang.haskell.general/14860 Blog noise [68]Haskell news from the blogosphere. * [69]Writing a Simple Search Engine in Haskell: Part 0 - Introduction * [70]Writing a Simple Search Engine in Haskell: Part 1 Maybe and List * [71]Haskell IO for Imperative Programmers * [72]Quotient Types for Information Hiding * [73]How Many Functions are There of Type Bool -> Bool? * [74]Macros for Haskell? Done. * [75]More on Haskell, Side Effects and Code Reuse * [76]The theory of monads * [77]Writing code by types * [78]Haskell: open secret in Ruby land * [79]Ruby vs Haskell: choose what works * [80]Real time Haskell * [81]Folds and functional programming * [82]Countable Ordinals in Haskell * [83]Haskell * [84]Programming and the Metaphorical Mind * [85]Languages and the semiskilled developer * [86]Building a Firewall Against Complexity * [87]The Killer App for a new language * [88]Time travel in Haskell * [89]Comonads and reading from the future * [90]Flirting with Functional Programming * [91]A fold-like procedure in C * [92]Monads in Qi * [93]Monads work because they have a tight interface * [94]What's wrong with for loops * [95]More on what's wrong with for loops * [96]Haskell, CAL and Scala * [97]Haskell: Queues without pointers * [98]Type Classes: Not Quite Overloading * [99]Generalised Algebraic Data Types, Phantom Types, and Dependent Types * [100]An IRC client/server in Haskell * [101]Language design: grand architecture versus feature collections * [102]Thoughts on one week in Haskell * [103]Why its hard for imperative programmers to learn Haskell * [104]Refunctoring with polymorphism * [105]Introductory console IO in Haskell * [106]Learn the lambda calculus * [107]Haskell for Alphas and Betas * [108]My evolution as a Haskell programmer * [109]On learning Haskell * [110]Greenspun's Tenth Rule applied to Haskell * [111]Cabal with rpm goodness * [112]F# * [113]Arithemtic coding in Haskell * [114]A filesystem tree printer * [115]Using Bayesian filtering instead of 'if' in Haskell * [116]Combinator parsing * [117]Monads for vector spaces, probability and quantum mechanics pt. I * [118]Monads, Vector Spaces and Quantum Mechanics pt. II * [119]Learning the Haskell programming language * [120]A twisted history of monad transformers * [121]Monadic parsing * [122]Forth as a Haskell DSL * [123]A better environment for shell scripting * [124]Smart classification using Bayesian monads in Haskell * [125]Haskell like data structures in Common Lisp 68. http://planet.haskell.org/ 69. http://blogs.nubgames.com/code/?p=18 70. http://blogs.nubgames.com/code/?p=19 71. http://blogs.nubgames.com/code/?p=22 72. http://japple.blogspot.com/2007/01/quotient-types-for-information-hiding.ht… 73. http://japple.blogspot.com/2007/01/how-many-functions-are-there-of-type.html 74. http://clemens.endorphin.org/weblog/archives/2007-01.shtml#e2007-01-31T12_2… 75. http://neilbartlett.name/blog/?p=13 76. http://scienceblogs.com/goodmath/2007/01/the_theory_of_monads_and_the_m_1.p… 77. http://neilmitchell.blogspot.com/2007/01/writing-code-by-types.html 78. http://notes-on-haskell.blogspot.com/2007/01/haskell-open-secret.html 79. http://notes-on-haskell.blogspot.com/2007/01/ruby-vs-haskell-choose-what-wo… 80. http://mikeburrell.wordpress.com/2007/02/01/real-time-haskell/ 81. http://mikeburrell.wordpress.com/2007/02/01/functional-idempotence-optimiza… 82. http://japple.blogspot.com/2007/02/countable-ordinals-in-haskell.html 83. http://vanirsystems.com/danielsblog/?p=103 84. http://toomuchcode.blogspot.com/2007/02/part-1-programming-and-metaphorical… 85. http://toomuchcode.blogspot.com/2007/02/part-2-languages-and-lesser-skilled… 86. http://toomuchcode.blogspot.com/2007/02/building-firewall-against-complexit… 87. http://toomuchcode.blogspot.com/2007/02/part-4-killer-app.html 88. http://community.livejournal.com/evan_tech/216270.html 89. http://sigfpe.blogspot.com/2007/02/comonads-and-reading-from-future.html 90. http://johnleesmiller.blogspot.com/2007/02/first-post.html 91. http://www.yomi.at/archive/2007/02/115 92. http://programmingkungfuqi.blogspot.com/2007/02/monads-in-qi.html 93. http://www.sdowney.org/2007/01/monads-rest-and-c-template.html 94. http://notes-on-haskell.blogspot.com/2007/02/whats-wrong-with-for-loop.html 95. http://notes-on-haskell.blogspot.com/2007/02/whats-wrong-with-for-loop-revi… 96. http://blog.tmorris.net/ignorance-is-mostly-bliss-but-not-always/ 97. http://www.randomhacks.net/articles/2007/02/08/haskell-queues-without-point… 98. http://www.cs.nott.ac.uk/~pni/Papers/Notes/typeClassOvld.html 99. http://www.cs.nott.ac.uk/~pni/Papers/Notes/GADTs.html 100. http://blog.nurd.se/hype/?p=30 101. http://www.dysfunctor.org/2007/02/13/architecture-vs-features/ 102. http://kevin.scaldeferri.com/blog/2007/02/12/OneWeek.html 103. http://qftblog.wordpress.com/2007/02/14/why-its-so-hard-for-imperative-prog… 104. http://blog.tmorris.net/refunctoring/ 105. http://cod3po37ry.blogspot.com/2007/02/more-on-haskell-io-and-interact.html 106. http://foreigndispatches.typepad.com/dispatches/2007/02/an_introduction.html 107. http://paulspontifications.blogspot.com/2007/02/haskell-for-alphas-and-beta… 108. http://onthebalcony.wordpress.com/2007/02/19/my-evolution-as-a-haskell-prog… 109. http://osfameron.vox.com/library/post/on-learning-haskell.html 110. http://japple.blogspot.com/2007/02/conors-rule.html 111. http://www.serpentine.com/blog/2007/02/20/haskell-cabal-now-with-extra-crun… 112. http://reddevnews.com/news/devnews/article.aspx?editorialsid=164 113. http://vandreev.wordpress.com/2007/01/07/arithmetic-coding/ 114. http://blog.moertel.com/articles/2007/02/22/a-simple-directory-tree-printer… 115. http://www.randomhacks.net/articles/2007/02/22/bayes-rule-and-drug-tests 116. http://mikeburrell.wordpress.com/2007/02/25/combinator-parsing/ 117. http://sigfpe.blogspot.com/2007/02/monads-for-vector-spaces-probability.html 118. http://sigfpe.wordpress.com/2007/03/04/monads-vector-spaces-and-quantum-mec… 119. http://printf.wordpress.com/2007/02/27/haskell-functional-programming-langu… 120. http://conway.rutgers.edu/~ccshan/wiki/blog/posts/Monad_transformers.html 121. http://gbacon.blogspot.com/2007/02/my-first-monadic-program.html 122. http://shaurz.wordpress.com/2007/03/03/forth-as-a-haskell-dsl-or-lambda-the… 123. http://changelog.complete.org/posts/587-A-better-environment-for-shell-scri… 124. http://www.randomhacks.net/articles/2007/03/03/smart-classification-with-ha… 125. http://common-lisp.net/project/patty/patty.html Quotes of the Week * sleepingsquirrel: Programming in Haskell is like having an interactive conversation with a teleportation machine. You tell it you want to go to some place warm and sandy. The machine complains about ambiguous constraints. So you tell it that there should be plenty of free tropical fruit drinks. It carps 'Inferred location less polymorphic than expected'. Whoops, free flowing that is... After a few more iterations, there's a little puff of smoke, and at the sound of the chimes, you discover you're now on the beach in Tahiti. And although you've used the machine many times before, you can't help but be impressed that it usually 'Just works' most of the time. * jmillikin: If I had to work on code with performance requirements, Haskell would be my choice (followed by C++). Haskell has functional goodness with the ability to break into imperative mode, and C++ gives me direct memory management with a few functional pieces. * Cale: It ought to be called simonPerformIO, and only used if your first name is Simon * monochrom: m a -> (a -> m b) -> m b is much more to the point than 'mumble computation mumble computation' * mwc: There's a time when your brain doesn't get the monads. Then something violent and irreversable happens and you hate every other language for not having monads Code Watch Wed Feb 28 05:07:14 PST 2007. Simon Marlow. [126]Remove vectored returns. We recently discovered that they aren't a win any more, and just cost code size. 126. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/19418 Wed Feb 21 09:04:01 PST 2007. simonpj. [127]Allow GADT syntax for newtypes 127. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/19344 About the Haskell Weekly News Each week, new editions are posted to [128]the Haskell mailing list as well as to [129]the Haskell Sequence and [130]Planet Haskell. [131]RSS is also available, and headlines appear on [132]haskell.org. Headlines are available as [133]PDF. To help create new editions of this newsletter, please see the [134]contributing information. Send stories to dons at cse.unsw.edu.au. The darcs repository is available at darcs get [135]http://www.cse.unsw.edu.au/~dons/code/hwn 128. http://www.haskell.org/mailman/listinfo/haskell 129. http://sequence.complete.org/ 130. http://planet.haskell.org/ 131. http://sequence.complete.org/node/feed 132. http://haskell.org/ 133. http://www.cse.unsw.edu.au/~dons/code/hwn/archives/20070305.pdf 134. http://haskell.org/haskellwiki/HWN 135. http://www.cse.unsw.edu.au/~dons/code/hwn

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Re: ANN: HSH 1.2.0
by Dave Feustel 05 Mar '07

05 Mar '07

> > On 2007-03-04, Dave(a)haskell.org, "Feustel <dfeustel"@mindspring.com <Dave(a)haskell.org> wrote: > > >> The Makefile in the HSH distribution should do this for you. But you > > >> can say: > > >> > > >> ghc --make -o setup -package Cabal Setup.lhs > > > > > > A40:/home/daf/Hsh/hsh}ghc --make -o setup -package Cabal Setu.lhs > > > ghc-6.2.2: unknown package name: Cabal > > > > Ahh. You will certainly need GHC 6.6 for HSH; see the list of > > prerequisites in the README or at > > http://software.complete.org/hsh/wiki/RelatedSoftware > > > > > gmake[1]: *** [Linker.o] Error 1 > > > gmake: *** [stage1] Error 1 > > > A40:/home/daf/Ghc/ghc-6.6} > > > > > > I'm not quite sure what to do with MAP_32BIT since I'm running in > > > AMD 64-bit mode. Any suggestions? > > > > This is out of my league to answer, but if you tell us about your > > platform, I bet we can find you some precompiled binaries for it. > > > > -- John > > I'm running AMD 64-bit OpenBSD 4.0. There is a downlevel package for ghc. > > I think I have found the cause of the undefined MAP_ANONYMOUS. It > looks like that symbol was changed to MAP_ANON in sys/mmap.h for > OpenBSD. I fixed(?) that and now the MAP_32BIT symbol is the current > roadblock. As far as I can tell, this symbol is not defined anywhere > in OpenBSD at the moment. I've done some googling but I still don't > know what to do with this symbol. Since there seems to be no MAP_32BIT in OpenBSD, I set the symbol to 0 and gmake got through Linker.c. Gmake now is running toward completion of the make. I have my fingers crossed :-).

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Re: ANN: HSH 1.2.0
by Dave Feustel 05 Mar '07

05 Mar '07

> On 2007-03-04, Dave(a)haskell.org, "Feustel <dfeustel"@mindspring.com <Dave(a)haskell.org> wrote: > >> The Makefile in the HSH distribution should do this for you. But you > >> can say: > >> > >> ghc --make -o setup -package Cabal Setup.lhs > > > > A40:/home/daf/Hsh/hsh}ghc --make -o setup -package Cabal Setu.lhs > > ghc-6.2.2: unknown package name: Cabal > > Ahh. You will certainly need GHC 6.6 for HSH; see the list of > prerequisites in the README or at > http://software.complete.org/hsh/wiki/RelatedSoftware > > > gmake[1]: *** [Linker.o] Error 1 > > gmake: *** [stage1] Error 1 > > A40:/home/daf/Ghc/ghc-6.6} > > > > I'm not quite sure what to do with MAP_32BIT since I'm running in > > AMD 64-bit mode. Any suggestions? > > This is out of my league to answer, but if you tell us about your > platform, I bet we can find you some precompiled binaries for it. > > -- John I'm running AMD 64-bit OpenBSD 4.0. There is a downlevel package for ghc. I think I have found the cause of the undefined MAP_ANONYMOUS. It looks like that symbol was changed to MAP_ANON in sys/mmap.h for OpenBSD. I fixed(?) that and now the MAP_32BIT symbol is the current roadblock. As far as I can tell, this symbol is not defined anywhere in OpenBSD at the moment. I've done some googling but I still don't know what to do with this symbol.

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Re: ANN: HSH 1.2.0
by unknown＠example.com 05 Mar '07

05 Mar '07

> The Makefile in the HSH distribution should do this for you. But you > can say: > > ghc --make -o setup -package Cabal Setup.lhs A40:/home/daf/Hsh/hsh}ghc --make -o setup -package Cabal Setu.lhs ghc-6.2.2: unknown package name: Cabal I'm working on getting ghc 6.6 built and installed. Gmake Currently exits on these errors: == gmake all -r; in /home/daf/Ghc/ghc-6.6/compiler ------------------------------------------------------------------------ ------------------------------------------------------------------------ == gmake all -r; in /home/daf/Ghc/ghc-6.6/rts ------------------------------------------------------------------------ ../compiler/ghc-inplace -optc-O -optc-L/usr/local/lib -optc-Wall -optc-W -optc-Wstrict-prototypes -optc-Wmissing-prototypes -optc-Wmissing-declarations -optc-Winline -optc-Waggregate-return -optc-Wbad-function-cast -optc-I../includes -optc-I. -optc-Iparallel -optc-DCOMPILING_RTS -optc-fomit-frame-pointer -optc-fno-strict-aliasing -H16m -O -L/usr/local/lib -optc-O2 -static -I. -#include HCIncludes.h -optc-fno-stack-protector -fvia-C -dcmm-lint -c Linker.c -o Linker.o Linker.c: In function `addDLL': Linker.c:1026: warning: assignment discards qualifiers from pointer target type Linker.c: In function `loadObj': Linker.c:1350: error: `MAP_32BIT' undeclared (first use in this function) Linker.c:1350: error: (Each undeclared identifier is reported only once Linker.c:1350: error: for each function it appears in.) Linker.c: In function `x86_64_high_symbol': Linker.c:2789: error: `MAP_32BIT' undeclared (first use in this function) Linker.c:2789: error: `MAP_ANONYMOUS' undeclared (first use in this function) gmake[1]: *** [Linker.o] Error 1 gmake: *** [stage1] Error 1 A40:/home/daf/Ghc/ghc-6.6} I'm not quite sure what to do with MAP_32BIT since I'm running in AMD 64-bit mode. Any suggestions? > ./setup configure > ./setup build > (as root) ./setup install > > > On 2007-03-03, dfeustel(a)mindspring.com <dfeustel(a)mindspring.com> wrote: > > I just tried to make HSH 1.2 but it needs Cabal, which I > > apparently don't have installed. I also don't have > > runghc installed (referenced at cabal homepage). Using > > ghc instead failed as follows: > > > > > > Setup.lhs:2: > > Failed to load interface for `Distribution.Simple': > > *** Deleting temp files > > Deleting: /home/daf/Tmp/ghc27809.hc /home/daf/Tmp/ghc27809.lpp > > Warning: deleting non-existent /home/daf/Tmp/ghc27809.hc > > A40:/home/daf/Hsh/hsh}ghc Setup.lhs configure > > > > Setup.lhs:2: > > Failed to load interface for `Distribution.Simple': > > A40:/home/daf/Hsh/hsh} > > > > This suggests to me that my Haskell setup is not complete. > > > > What do I need to do to get to the point where I can build HSH? > > > > Thanks. > > > -- > John Goerzen > Author, Foundations of Python Network Programming > http://www.amazon.com/exec/obidos/tg/detail/-/1590593715 > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: ANN: HSH 1.2.0
by dfeustel＠mindspring.com 05 Mar '07

05 Mar '07

I just tried to make HSH 1.2 but it needs Cabal, which I apparently don't have installed. I also don't have runghc installed (referenced at cabal homepage). Using ghc instead failed as follows: Setup.lhs:2: Failed to load interface for `Distribution.Simple': *** Deleting temp files Deleting: /home/daf/Tmp/ghc27809.hc /home/daf/Tmp/ghc27809.lpp Warning: deleting non-existent /home/daf/Tmp/ghc27809.hc A40:/home/daf/Hsh/hsh}ghc Setup.lhs configure Setup.lhs:2: Failed to load interface for `Distribution.Simple': A40:/home/daf/Hsh/hsh} This suggests to me that my Haskell setup is not complete. What do I need to do to get to the point where I can build HSH? Thanks.

3 2

Any interested authors?
by Antonio Cangiano 05 Mar '07

05 Mar '07

Dave Thomas (from The Pragmatic Programmers, not from Wendy's :)) has announced an Erlang book (http://www.pragmaticprogrammer.com/titles/jaerlang/) in the Ruby mailing list. A few responses showed an interest in a similar book for Haskell. You can see the thread here: http://tinyurl.com/2ecpsn. Dave answered such requests by saying: "I'd love to do one. It's a question of finding the right author.". If you think this would be up your alley, perhaps you could contact Dave in regards to this matter. Just a heads up, from a potential reader. :) Regards, Antonio -- http://antoniocangiano.com Zen and the Art of Ruby Programming

1 0

Safe top-level IORefs
by Roberto Zunino 05 Mar '07

05 Mar '07

I'm posting the code of a module, IORefs, allowing top-level IORefs to be safely declared and used. Usafety reports are welcome. Tested in GHC 6.6. ** Features: 1) IORef a provided for any Typeable a 2) An unbounded number of IORef's can be declared 3) An IORef declaration is 3 lines long (+ optional type signature) 4) Each IORef has its own starting value 5) Referential transparency: no NOINLINE, no unsafePerformIO is needed in the user module 6) Negligible overhead: O(1) in the usual usage pattern (neglecting a O(log n) setup phase) ** Usage: import Data.Typeable import Data.IORef import IORefs data X deriving Typeable -- the actual name of the IORef instance IORefDefault X Int where ioRefDefault _ = 42 -- type+default x = ioRef (undefined :: X) -- a convenient name for the IORef x :: IORef Int -- optional signature -- Still the same IORef as x ! y :: IORef Int y = ioRef (undefined :: X) main = do let printX = readIORef x >>= print printX -- 42 writeIORef x 3 printX -- 3 modifyIORef x succ printX -- 4 modifyIORef y succ -- y is equal to x, so... printX -- 5 -- ... the above is actually equivalent to modifyIORef (ioRef (undefined :: X) :: IORef Int) succ printX -- 6 Passing a non _|_ value to ioRef does not break the abstraction: ioRef ignores this value. Similarly, ioRef always calls ioRefDefault with _|_, so writing (ioRef (X1 :: X)) and (ioRef (X2 :: X)) will not cause the initial value to be ill-defined, i.e. depending on which expression is evaluated first. On performance: ioRef takes O(log n) to return, where n is the number of refs previous created by ioRef. In the common usage pattern, ioRef is used only in a top-level definition. If no inlining happens, we pay only a startup cost: then all IORefs are available in O(1). If inlining happens, or if we use ioRef as in the last lines of main above, we pay the log(n) price. Note that inlining only affects the performance, and not the semantics. Assumptions/known glitches: 1) We rely on cast from Typeable 2) GHCi is known not to reinitialize the refs on reload. 3) No multithreading support for now. 4) The IORefs module uses a memoization technique, relying on a "classic" top-level IORef declared through NOINLINE + unsafePerformIO. Regards, Zun. =========================================================================== {-# OPTIONS_GHC -Wall -fglasgow-exts #-} module IORefs (ioRef, IORefDefault, ioRefDefault) where import qualified Data.Map as M import System.IO.Unsafe import Data.IORef import Data.Typeable class (Typeable a, Typeable b) => IORefDefault a b | a -> b where ioRefDefault :: a -> b data Ref = forall a . Typeable a => Ref (IORef a) type RefMap = M.Map TypeRep Ref {-# NOINLINE refs #-} -- This is crucial refs :: IORef RefMap refs = unsafePerformIO $ newIORef M.empty -- This is like a memoized function, so inlining this should be safe. -- (Needs locking for multithread, though.) ioRef :: forall a b . IORefDefault a b => a -> IORef b ioRef x = unsafePerformIO $ do rs <- readIORef refs case typeOf x `M.lookup` rs of Nothing -> do ref <- newIORef $ ioRefDefault (undefined :: a) writeIORef refs $ M.insert (typeOf x) (Ref ref) rs return ref Just (Ref aRef) -> case cast aRef of Nothing -> error $ "ioRef: impossible!" Just ref -> return ref -- Should be in Data.Typeable instance Ord TypeRep where compare x y = compare (show x) (show y)

2 2

Non-exported type classes?
by Roberto Zunino 04 Mar '07

04 Mar '07

What is the effect of declaring a class in a module and not exporting it? Would that prevent to add more instances to that class other than those already defined in the module? More in detail, consider this module: === module Peano (Z,S,C) where data Z data S a -- Not exported class Peano b where instance Peano Z where instance Peano a => Peano (S a) where -- Exported class Peano a => C a where === Would that limit the instances of the class C to the Peano type naturals? Thanks, Roberto Zunino.

3 2

is there already a function that does this?
by Jared Jennings 04 Mar '07

04 Mar '07

-- Sort the [a]'s by the [b]'s. sortByKeys :: (Ord b) => [b] -> [a] -> [a] sortByKeys keys values = map snd $ sortBy compareFst (zip keys values) where compareFst x y = compare (fst x) (fst y) -- Sort a list by an IO-returning compare function. sortByM :: (Monad m, Ord b) => (a -> m b) -> [a] -> m [a] sortByM fun lis = mapM fun lis >>= \keys -> return $ sortByKeys keys lis Is there a function that can make sortByM out of sortByKeys? I don't know of one, but having been writing haskell for a few weeks, it sort of smells to me like there probably is one.

4 3

RE: MPTCs and rigid variables
by C Rodrigues 04 Mar '07

04 Mar '07

>{-# OPTIONS_GHC -fglasgow-exts #-} > >class Foo a b | a -> b where > foo :: Foo b c => a -> Maybe c > >instance Foo String () where foo _ = Nothing >instance Foo Int String where foo 4 = Just (); foo _ = Nothing > There appears to be a type-safe way to use unsafeCoerce# for this: -------- import qualified GHC.Exts class Foo a b | a -> b where foo :: a -> FooBox b data FooBox b = forall c. Foo b c => FooBox (Maybe c) instance Foo () () instance Foo String () where foo _ = FooBox Nothing instance Foo Int String where foo 4 = FooBox $ Just (); foo _ = FooBox Nothing runFoo :: (Foo a b, Foo b c) => a -> Maybe c runFoo x = case foo x of FooBox x -> GHC.Exts.unsafeCoerce# x -------- The class constraint check of a,b,c gets moved to the runFoo method instead of the instance declarations. Between the body of foo and the call to foo in runFoo, type 'c' is unknown to the compiler, so we have to encapsulate it in a FooBox. The unsafeCoerce# is safe because the type constraint (Foo b c) that we've placed both on FooBox and on runFoo permits c to have only the type uniquely specified by b. We actually could remove the Foo constraint on FooBox, which makes the code no longer typesafe but it will still work just fine. _________________________________________________________________ Dont miss your chance to WIN 10 hours of private jet travel from Microsoft® Office Live http://clk.atdmt.com/MRT/go/mcrssaub0540002499mrt/direct/01/

2 1

Proposal: simple interface to libraries Haddock
by David House 04 Mar '07

04 Mar '07

Hey all, I'm proposing something simple that should make it easier for both Haskell programmers and Haskell tool writers to find the documentation for a function. We need a simple URL for the Haddock docs of any function. PHP has this already: just hit php.net/funcname for the documentation for funcname(). My proposal is similarly simple: http://docs.haskell.org/funcname A CGI script would find funcname in the index and redirect to the URL of the docs for funcname. The only contentious issue is what to do in case of ambiguous lookups; i.e. would docs.haskell.org/lookup be Data.Map.lookup, or Data.List.lookup? My suggestion is that we present a page saying 'which function did you mean?'. We should also allow a way to be unambiguous in the URL: http://docs.haskell.org/Data.Map.funcname Pros: 1) It's really easy to find the documentation for any function. 2) It's really easy to write a tool that finds documentation for a function (including Firefox keywords, Emacs/Vim integration, GHCi integration and so on). Any comments? -- -David House, dmhouse(a)gmail.com

5 10

instance Eq Exception??
by Isaac Dupree 04 Mar '07

04 Mar '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 It seems the Exception datatype is currently an instance of Eq, that does not even satisfy reflexivity (for Dynamic exceptions). Does anybody use this? What is it good for? Why is it there? What if we delete the instance because it doesn't make sense? Exception is not an instance of Ord currently; it also has an instance Show that does make a little sense - for Dynamic exceptions, it gives (in GHC, not Hugs) the information of what the exception's type looks like. Isaac -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.3 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFF6bSNHgcxvIWYTTURArNRAJwMmp/keolibaZggANLCe5IMdit7ACcDZkp 1WP7Fkdj36ZEeHxHFem1py8= =gkfv -----END PGP SIGNATURE-----

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Re: [Haskell-cafe] MPTCs and rigid variables
by David House 04 Mar '07

04 Mar '07

On 03/03/07, Bryan Burgers <bryan.burgers(a)gmail.com> wrote: > As far as I know, you should be defining the type of bar in the class > declaration for Foo, not in an instance declaration. I think I over-reduced my problem. Here's a more complex issue that can't be resolved by moving bar to be a method of the class: {-# OPTIONS_GHC -fglasgow-exts #-} class Foo a b | a -> b where foo :: Foo b c => a -> Maybe c instance Foo String () where foo _ = Nothing instance Foo Int String where foo 4 = Just (); foo _ = Nothing -- -David House, dmhouse(a)gmail.com

1 0

An HSH case study
by John Goerzen 03 Mar '07

03 Mar '07

Some of you may be interested in my recent blog post[1], where I discuss porting hg-buildpackage[2] from a set of shell scripts to a set of Haskell programs that use HSH. To my surprise, I achieved a 20% *reduction* in source lines of code, while doing the exact same tasks. I guess I have to consider switching more code to HSH. Purely in the interests of science, of course ;-) [1] http://changelog.complete.org/posts/587-A-better-environment-for-shell-scri… [2] http://hg.complete.org/hg-buildpackage

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ANN: HSH 1.0.0
by John Goerzen 03 Mar '07

03 Mar '07

Hello, I'm pleased to announce the first release of HSH. HSH is designed to let you mix and match shell expressions with Haskell programs. With HSH, it is possible to easily run shell commands, capture their output or provide their input, and pipe them to/from other shell commands and arbitrary Haskell functions at will. HSH makes it easy to run shell commands. But its real power is in piping. You can pipe -- arbitrarily -- between external programs, pure Haskell functions, and Haskell IO functions, mixing and matching at will. Here are a few examples to get you started: runS $ "echo /etc/pass*" -> "/etc/passwd /etc/passwd-" run $ "ls -l" -|- "wc -l" -> 12 run $ "ls -l" -|- wcL -> 12 wcL is a pure Haskell function: wcL :: [String] -> [String] wcL inp = [show $ genericLength inp] More information, including downloads and further examples, is at the HSH homepage: http://software.complete.org/hsh -- John

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Very Basic IO question
by Joe Olivas 03 Mar '07

03 Mar '07

I am VERY new to Haskell, and just getting my feet wet with functional programming in general. I've been going over a few examples online, but I can't figure out the behavior I'm seeing on a very basic example: --- module Main where import System.IO main :: IO () main = do putStrLn "Please enter your name: " name <- getLine putStrLn ("Hello, " ++ name ++ ", how are you?") --- This example works as I would expect. The prompt displays with a new line, the input is entered and echoed: --- Please enter your name: joe Hello, joe, how are you? However, changing 'putStrLn' to 'putStr' does not do what I would expect. The prompt doesn't get displayed until after there is input: --- joe Please enter your name: Hello, joe, how are you? Why does it exhibit this behavior? I'm using a ghc 6.6 built from source from 20070227. The regular 6.6 release had the same behavior. Any help would be greatly appreciated. -Joe -- Using Opera's revolutionary e-mail client: http://www.opera.com/mail/

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Hi I need help for very simple question!
by iliali16 03 Mar '07

03 Mar '07

Hi Haskell People, I have problem implementing one function. I think my idea is write but I have minor mistakes which I cannot get right since I progrem Haskell from very recently. No the function is called intoWords and has to take a string of any size and kind of characters.No I have to produce as output a list of strings.To have a rule which defines an element from the list is the space character which can also be included in the string.So what i think should be smth like. intoWord Hello my name is Smart should produse a list looking like [Hello,my,name,is,Smart] Now I tried to do it recucively to take the string and checks if an element is white space in the list using the isSPace build in function. This is my code please help me if you have any suggestions. Also I don't know how to produce a base case for my recursion. import Char intoWords ::String -> [String] intoWords (x:xs) |isSpace x = intoWords xs |otherwise = xs Thanks in advance for any suggestions. I really want to understand this bloody function couse I've been tring for a week now and I have tried so many ways to produce it that now I am fed up with it and I want to know how should it work since I am curious now. -- View this message in context: http://www.nabble.com/Hi-I-need-help-for-very-simple-question%21-tf3334486.… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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numeric minimization in Haskell
by Chad Scherrer 03 Mar '07

03 Mar '07

Does anyone know of any Haskell code for numeric minimization? I was thinking conjugate gradient would be good, but at this point I'd be happy with anything. I've found some code written by Tomasz Cholewo at http://ci.uofl.edu/tom/software/Haskell/ but it requires importing his "Arr.lhs" library, which is not publicly available. The only other thing I've been able to dig up is this www.st.cs.ru.nl/papers/1997/serp97-cgfunctional.ps.gz which suggests Haskell is slow for such problems. I suspect this was an implementation issue, so I don't think their code would be very helpful (though it would be nice to tidy it up and demonstrate the improvement - could it beat the Clean implementation they give?) The other possibility I was considering was using Alberto Ruiz's wrapper for the GSL library http://dis.um.es/~alberto/GSLHaskell/ The only problems with this are (1) requires having GSL available, so it's not as portable, and (2) does everything in terms of lists, which requires a lot of translations to and from lists (I'm using mutable arrays). If there's nothing already written that works together, one of these should give me a start, but I'd like to avoid reinventing the wheel if possible. Thanks! -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

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Takusen and strictness
by Paul Moore 03 Mar '07

03 Mar '07

I'm still fiddling with simple database queries using Takusen. One question I have is regarding strictness. I've just been reading "Haskell IO for Imperative Programmers" and loved the idea that laziness (rather than monads) is what makes IO in Haskell so simple. What I'm not sure about, is whether Takusen offers a way of lazily getting data from a database (and a meta-question - how do I work this out for mysefl?!) With the code {-# OPTIONS -fglasgow-exts #-} import Database.Oracle.Enumerator import Database.Enumerator runSql :: String -> IO [String] runSql s = withSession (connect "USER" "PASSWD" "DB") ( do let iter (s::String) accum = result (s : accum) r <- doQuery (sql s) iter [] return r ) main :: IO () main = do r <- runSql "select username from all_users" putStrLn (unlines r) I can do a simple database query, process the results, and produce output. The sreucture of main is much like an interact loop, but with the input from a database rather than stdin. But, will this read the database lazily, or will it get all the rows into memory at once? How will using result' instead of result (in runSql) affect this? And as I said above, how can I learn to work this out for myself? I know I could just ignore the issue until performance becomes a problem and then profile - but that ignores the question of whether I've got the idiom right. Thanks for any help, Paul.

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Re: [Haskell] Laziness and the IO Monad (randomness)
by Kirsten Chevalier 02 Mar '07

02 Mar '07

[redirecting to haskell-cafe] On 3/1/07, Dave Tapley <dukedave(a)gmail.com> wrote: > However this latter case gets stuck in an infinite loop, terminating on a stack overflow. > > My question asks why this is the case, when laziness should ensure only the first 10 cases need to be computed. > You didn't say which function you had narrowed down the stack overflow to, but I suspect it's here: > firstTen :: IO [Int] > firstTen = do > infiniteNums <- iterateM addRand randNum > return (take 10 infiniteNums) In order for IO to work the way you'd expect, you have to be able to specify which IO operations happen in what order, which is exactly what a do-block within the IO monad specifies. But specifying the order of operations also means specifying in what order evaluation happens. So, the code you've written means "evaluate infiniteNums fully (in order that we might do whatever IO operations it involves before the return statement), then return the first 10 elements of its result." Since you're forcing evaluation of an infinite list, the program loops infinitely. If you find this counter-intuitive, you wouldn't be the first, but there's no other sensible interpretation for the code you've written. Deferring evaluation of infiniteNums in this case would mean that IO would happen in a strange and unpredictable order (or if it actually wouldn't, then the compiler isn't smart enough to know that.) I would solve this problem by writing a version of iterateM that takes the length of the desired list as an argument (e.g., 10 in your example), which sadly breaks modularity, but as I explained above, working within the IO monad necessitates that. Someone more l33t than me may be able to suggest a more elegant solution, though. Cheers, Kirsten -- Kirsten Chevalier* chevalier(a)alum.wellesley.edu *Often in error, never in doubt "They killed, they maimed, and they called information for numbers they could easily look up in the book." -- Woody Allen

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splitting strings
by h. 02 Mar '07

02 Mar '07

Hello, I wrote the following split function for Strings: splitS :: String -> String -> [String] splitS a b = splitA a b where z = length b - 1 splitA [] _ = [""] splitA (c:cs) (d:ds) | c == d && fst s == ds = "" : splitA (snd s) b | otherwise = (c : head r) : tail r where r = splitA cs b s = splitAt z cs example: splitS "Test;Hello;+123.5;+ 7" ";+" -> ["Test;Hallo","123.5"," 7"] How could it be optimized on speed? Does there exist already an optimized split for the conventional String type? -- Thanks in advance for your answer. h.

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Using loop fusion for writing efficent high-level code Re[2]: [Haskell] [Fwd: Re: Computer Language Shootout]
by Bulat Ziganshin 02 Mar '07

02 Mar '07

Hello Duncan, Tuesday, February 27, 2007, 1:09:53 PM, you wrote: can you please provide examples of such code? the ultimate goal is to have tutorial on writing efficient code in high-level manner, but that is too ambitious. just some examples with a little explanation of how this is compiled? thanks in advance >> So I think we should do the same. It even shows in the Shootout - the >> programs that are simultaneously fastest and clearest are not pure >> Haskell, but delegate their innermost loops to tuned C libraries (FPS >> and GMP). > I should note that FPS is almost completely Haskell code, not C. We use > C for things like memcmp, memcpy, memset, reverse_copy, intersperse, > maximum, minimum and count. > Certainly some of the innards are low level style Haskell, though not > the kind that could be replicated in C because we use high level > transformations to fuse loop bodies together and wrap them in high > performance, low level loop code. > This is not the style where we just wrap well tuned C code, this is a > style where we generate high performance low level code from a high > level spec. This relies on GHC's excellent and programmable optimiser. > It's wrong to say that the shootout improvements were only down to > improved libraries. The performance of ByteString code improved very > significantly between GHC 6.4 and 6.6 and a large part of that was down > to optimiser improvements (not just the ForeignPtr rep change). Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Re: [Haskell-cafe] Re: OO Design in Haskell
by P. R. Stanley 02 Mar '07

02 Mar '07

>Hi > >>forgive my ignorance but I thought functional programming was a >>mathematically sound framework unlike Object Oriented programming. > >Referentially transparent is a better term than mathematically sound >here. This is the property that x = y means that instances of x can be >replaced with y. >Could you elaborate please? >>Isn't using Haskell for OOP kind of defeating the whole object? > >It is defeating the point of expressing programs in a beautiful way, >but if you are building it on top of Haskell, without going to things >like unsafePerformIO, then you still end up with a referentially >transparent framework. I suppose one thing OO has going for it is a useful system of organising your code. Beyond that I'm afraid it is open to the same issues which plagued the soft eng world in the 70s. Yet, everyone seems to be mad about it inthe business. Sorry if this is going slightly off-topic. Paul

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Build failed - hidden package ?
by Dunric 02 Mar '07

02 Mar '07

Hi. I've got stuck with the following compilation error I probably can't fully understand: ---------------------------------------------------------------------- Building library... ... Using package config file: /usr/local/lib/ghc-6.6/package.conf wired-in package base mapped to base-2.0 wired-in package rts mapped to rts-1.0 wired-in package haskell98 mapped to haskell98-1.0 wired-in package template-haskell mapped to template-haskell-2.0 Hsc static flags: -static ... Graphics/UI/SDL/Rotozoomer.hs:15:7: Could not find module `Foreign.C': it is a member of package base, which is hidden ---------------------------------------------------------------------- What does such error mean ? Modules Foreign and Foreign.C are installed and available from the default path. Lines 12-15 of Rotozoomer.hs: ------------------------------------------ module Graphics.UI.SDL.Rotozoomer where import Foreign import Foreign.C ------------------------------------------ Any idea what's wrong, resp. some explanation why compilation fails ? Thanks in an advance. ------------------------------------------ www.icqsms.cz

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Re: [Haskell-cafe] Re: OO Design in Haskell Example (Draft)
by Tim Docker 02 Mar '07

02 Mar '07

"Steve Downey" <sdowney(a)gmail.com> wrote: > I'm not sure, though, what would happen if I tried to > add state to the types. With the previous example, > using existentials to create a reference type that > holds elements of a type class that matches the interface, > I think that it would be natural to hold state by having > that element stored in a mutable state variable, and replacing > the held values. State is often best avoided, but if it's really what you want to do, you can still capture a mutable variable in the closures captured inside the record of functions. Tim import Data.IORef data Component = Component { draw :: IO (), move :: (Int,Int) -> IO () } newCircle :: IO Component newCircle = do pref <- newIORef (0,0) return Component{draw=draw' pref, move=move' pref} where draw' pref = do p <- readIORef pref putStrLn ("circle at " ++ show p) move' pref p = writeIORef pref p

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