September 2008 - Haskell-Cafe

nooby question on typing
by Han Joosten 13 Sep '08

13 Sep '08

Hi, I have a question about types in Haskell. I feel that I am overlooking some obvious solution, but I do not manage to get it right. Here is the plot: I have got 4 different types of 'rules', each with it's own constructor. So i defined: > type Rules = [Rule] > data Rule = RuRule > | SgRule > | GcRule > | FrRule > deriving (Eq,Show) > data RuRule > = Ru { rrsrt :: Char > , rrant :: Expression > , rrfps :: FilePos > } deriving (Eq,Show) > data SgRule > = Sg { srfps :: FilePos > , srsig :: Rule > , srxpl :: String > , srtyp :: (Concept,Concept) > } deriving (Eq,Show) > data GcRule > = Gc { grfps :: FilePos > , grspe :: Morphism > , grgen :: Expression > } deriving (Eq,Show) > data FrRule > = Fr { fraut :: AutType > , frdec :: Declaration > , frcmp :: Expression > , frpat :: String > } deriving (Eq,Show) Now I would like to be able to use these rules without knowing what kind they are, in lists, however i get errors like Couldn't match expected type `Rule' against inferred type `SgRule'. Is there any other (even trivial?) way to get this done? I know Haskell well enough to know that it is possible, but I don not know Haskell well enough to know how to do it :teeth: Any help is kindly appreciated! Han Joosten -- View this message in context: http://www.nabble.com/nooby-question-on-typing-tp19470727p19470727.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Fwd: Computer Language Benchmarks Game: [Which parallel problem would you add and why?]
by Don Stewart 13 Sep '08

13 Sep '08

The Computer Language Benchmarks Game has a quad core (as you probably know). But they're looking for new benchmarks. Ones that can actually exploit parallelism. If you've got suggestions on good parallelism benchmarks, and why they're good, add them to the alioth or reddit threads. ----- Forwarded message from Isaac Gouy ----- "Which parallel problem would you add and why?" http://alioth.debian.org/forum/forum.php?thread_id=14502&forum_id=2840 "Ask Proggit: Which parallel problem would you add now The Computer Language Benchmarks Game is measured on quad-core hardware, and why?" http://www.reddit.com/r/programming/comments/718qf/ask_proggit_which_parall… ----- End forwarded message -----

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Hackage needs a theme song!
by Jason Dagit 13 Sep '08

13 Sep '08

I realized tonight that Hackage needs a theme song. Here is my attempt at it, apologies to Jefferson Starship: We built this hackage, We built this hackage on lambda and types Say you don't know me, or the parameters I pass Say you don't care who instances this type class Knee deep in the thunk, value infinitely big Too many constraints eating up the type sig Main runs the Monad, Listen to the Reader Don't you remember? We built this hackage We built this hackage on lambda and types! We built this hackage, we built this hackage on lambda and types Built this hackage, we built this hackage on lambda and types Someone always playing package games Who cares they're always changing package names We just want to compile here, someone stole the type hack They call us lazy, evaluate us off the stack Main runs the Monad, Listen to the Reader Don't you remember? We built this hackage We built this hackage on lambda and types! We built this hackage, we built this hackage on lambda and types Built this hackage, we built this hackage on lambda and types It's just another version in our release style Cabal has got the build deps, and we upload the file Who counts the downloads underneath package node Who writes the type errors into our source code Don't tell us you need us, 'cause we're the db of tools Looking for pragmas, crawling through your RULES Don't you remember ... Main runs the Monad, Listen to the Reader - Don't you remember? We built this hackage, We built this hackage on lambda and types We built this hackage, we built this hackage on lambda and types Built this hackage, we built this hackage on lambda and types Built this hackage, we built this hackage on lambda and types Built this hackage, we built this hackage on lambda and types We built, we built this hackage yeah We built this hackage We built, we built this hackage (Repeat - fade)

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Windows details
by Andrew Coppin 13 Sep '08

13 Sep '08

I rather doubt anybody will know the answer to this, but I'll ask anyway... Under MS Windows, if you right-click on an executable file and select "properties", sometimes there's a "Version" tab that tells you the version number of the program. And sometimes there isn't. (Most especially, GHC-compiled programs do not have this tab.) Anybody know how to go about adding this? Also, anybody know how to give a GHC-compiled program a custom icon? If it's going to be really difficult then I won't bother, but it'd be interesting to know. (In other news, today I discovered that applying UPX to my 2.8 MB GHC-compiled executable shrinks it down to 800 KB and it still functions. And WinZip shrinks it down to just 300 KB. 2.8 MB for a program that just does a little text parsing does seem a touch excessive to me...)

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Erroneous package listings in hackage?
by Dougal Stanton 13 Sep '08

13 Sep '08

$ cabal update ... $ cabal list | less ... * cairo Latest version installed: 0.9.13 Homepage: http://haskell.org/gtk2hs/ License: BSD3 ... $ cabal install cairo cabal: There is no package named cairo I must admit I was surprised to see a gtk2hs module on Hackage, but not half as surprised when I found it wasn't there after all... D

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Windows console
by Andrew Coppin 13 Sep '08

13 Sep '08

When coding in a POSIX-compliant environment, you can usually write special escape codes to the console to change the text colour and so forth. However, this does not work on Windows. (Ignore all references you see to enabling ANSI.SYS in your config.sys file; this applies only to 16-bit MS-DOS programs, *not* to 32-bit Windows programs.) However - to my surprise - apparently the Win32 API provides a set of function calls that do in fact allow 32-bit applications to change the colours of the console on a character-by-character basis. However - wait for it - those *particular* functions aren't in Haskell's System.Win32.Console module. :-( Obviously, I know nothing about C. However, after much hunting around, it turns out that for some reason, GHC appears to ship with a complete set of C header files for the Win32 API. (In other words, the necessary header file for accessing the functions I want is there.) After staggering through the (very unhelpful) FFI language specification, I was able to make it so that I can apparently call these functions from Haskell. I was not, however, able to find any way at all to import the symbolic constants necessary, so I was forced to reading through the source code of the raw C header files to find out what the numeric values of these are (!!!) The long and short of it is, I now have a small Haskell library that enables me to print things in trippy colours on the screen from a normal Haskell CLI program. Yay for me! (Actually, you can also change the title on the window - so you can make your program say "My Fantastic Tool" instead of "C:\Documents and Settings\foo\Haskell\MyTool\MyTool.exe" in the titlebar. Again, this is for a normal Haskell console application with nothing done to it.) Would anybody else be interested in having this code? (Obviously, it's pretty tiny.) For that matter, would the maintainer of System.Win32.Console be interested in adding the necessary dozen lines of code to that module? Actually, now that I think about it, it would be kind of nice to have a magic package that writes out escape codes or calls the Win32 API depending on which platform your program is compiled on - in the style of System.FilePath. I don't know how to do that though... A nice idea, guys?

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ANN: Twidge
by John Goerzen 13 Sep '08

13 Sep '08

Hi folks, I've released Twidge, a command-line Twitter and Identi.ca client, written -- of course -- in Haskell. I'm pretty excited about it, but then hey, I'm biased. Anyhow, it's available from Hackage or from the homepage at: http://software.complete.org/twidge I've also got links to its (11-page!) manual as well as some HOWTOs and FAQs on the wiki at the above URL. Comments, patches welcome. Feel free to reply here or send them to @jgoerzen. -- John

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[Fwd: profiling in haskell]
by Vlad Skvortsov 13 Sep '08

13 Sep '08

Posting to cafe since I got just one reply on beginner@. I was suggested to include more SCC annotations, but that didn't help. The 'serialize' function is still reported to consume about 32% of running time, 29% inherited. However, functions called from it only account for about 3% of time. How do I get more insight into that? Thanks. -- Vlad Skvortsov, vss(a)73rus.com, http://vss.73rus.com

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uuid package on OS X
by Jason Dusek 12 Sep '08

12 Sep '08

The UUID package builds and runs fine on OS X without any need for `e2fsprog` -- just remove the `extra-libs` line from the Cabal file. (Apple put the UUID stuff in `libc`.) Has anyone tried to build it on Windows? -- _jsn |...UUID package...| http://hackage.haskell.org/cgi-bin/hackage-scripts/package/uuid

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Tons of retainers when inserting 611, 756 elements into a Trie
by Denis Bueno 12 Sep '08

12 Sep '08

Dear haskell-cafe, I've got an anagram-finder ("puzzler") that uses a "dictionary" datatype, which in turn uses a trie. In src/hs/Main.hs, I create a new dictionary from a word list (a file containing one word per line) and perform a query on it in order to force it to actually load something from disk. By problem is that though my word list is just shy of 7MB, puzzler occupies nearly 1GB of resident memory as soon as the dictionary is loaded. I'm using GHC 6.8.3 and Gtk2hs 0.9.13 on OS X 10.4.11. To see for yourself, check out the code with git and run it: $ git clone git://github.com/dbueno/puzzler.git $ git checkout -b origin/bsbench $ cabal configure # needs gtk2hs $ cabal build $ ./dist/build/puzzler/puzzler # look at the resident memory Retainer profiling (attachment "puzzler-hr.pdf") shows that `insertWith' on my trie is responsible for most of the memory. As you will see, in `makeDictionary' I try to strictly apply the combining function to combat these retainers. But the problem doesn't go away. More strangely: puzzler has a second executable, puzzler-test, which runs unit tests, including loading the exact same anagram query. However, puzzler-test never uses more than 250MB or so. The dictionary (in module Puzzler.Anagram) is an array of bytestrings paired with a Trie mapping bytestrings to sets of indices in the array. > data Dictionary = Dictionary > { dictWords :: Words > , sortWords :: Trie IntSet } > type Words = Array Int ByteString The Trie is a custom bytestring trie datatype. Each level is mapped to by the character it represents. If that character is a terminal character for some word (Right (t,x)), then that word maps to x. Otherwise no word ends at that character, but there may be longer words, so the trie continues with (Left t). > newtype Trie a = Trie { unTrie :: IntMap (Either (Trie a) (Trie a, a)) } > deriving (Eq, Ord, Show) The following is where _I think_ the error lies (src/hs/Puzzler/Anagram.hs): > -- | Creates an anagram dictionary from a file of words, one per line. The > -- words may be compound, as long as there is one per line. > createDictionary :: FilePath -> IO Dictionary > createDictionary path = (makeDictionary . lines) `liftM` readFile path > > -- | Makes an anagram dictionary from a list of words. > makeDictionary :: [ByteString] -> Dictionary > makeDictionary ws = Dictionary > { dictWords = dw > , sortWords = go end Trie.empty } > where > dw = listArray (0, length ws - 1) ws ; (begin, end) = bounds dw > go i t | seq t $ False = undefined > | i < begin = t > | otherwise = go (i-1) > -- $ Trie.insertWith Set.union (BS.sort (dw!i)) (Set.singleton i) t > $ insertWith' Set.union (BS.sort (dw!i)) (Set.singleton i) t > > insertWith' f k v m | seq k $ False = undefined > insertWith' f k v m = case Trie.lookup k m of > Nothing -> Trie.insert k v m > Just s -> (Trie.insert k $! f v s) m I've been scouring haskell-cafe for similar issues, and all seem to have been solved by a function similar to my `insertWith''. Uncommenting `Trie.insertWith' and commenting out the rest doesn't appear to differ noticeably in memory consumption. The implementation of `Trie.insertWith' is: > insertWith :: (a -> a -> a) -> ByteString -> a -> Trie a -> Trie a > insertWith f bs x t@(Trie m) = case uncons bs of > Nothing -> t > Just (c, cs) -> Trie (Map.alter myAlter (ord c) m) > where > myAlter Nothing = Just $ cons (insertWith f cs x empty, x) > myAlter (Just (Left t)) = Just $ cons (insertWith f cs x t, x) > myAlter (Just (Right (t,x'))) = > Just $ Right (insertWith f cs x t, if isLast then f x x' else x') > > -- If `cs' is empty then `c' is the last char of the word to insert; > -- that is, we're done. > cons (t, x) = if isLast then Right (t, x) else Left t > isLast = BS.null cs Any ideas? Denis

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