- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Iteratee, parsec & co.
by John Lato 09 Feb '10

09 Feb '10

> From: Edward Kmett <ekmett(a)gmail.com> > > 3. Why Seek FileOffset is error message? >> > > I'm not quite sure what you're asking here. One of the infelicities of iteratee-0.3 is that it defines a data type: > data ErrMsg = Err String > | Seek FileOffset > deriving (Show, Eq) I believe this is what the OP is referring to. Oleg originally implemented seek using IORefs; I wanted to try this and didn't know if it would work so I used a minimal implementation. I've decided this is the correct approach, but the details need to be tweaked a bit. Cheers, John

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various dependencies breakages
by Thomas Girod 09 Feb '10

09 Feb '10

Hi there. I'm trying to reinstall gitit after updating to ghc 6.12 and it's driving me crazy. I hope you will be able to help me troubleshoot this mess ... I'm starting from scratch again, using cabal. I will post more problems as they appears. $ cabal install gitit Resolving dependencies... cabal: cannot configure datetime-0.2. It requires QuickCheck ==2.* For the dependency on QuickCheck ==2.* there are these packages: QuickCheck-2.1, QuickCheck-2.1.0.1, QuickCheck-2.1.0.2 and QuickCheck-2.1.0.3. However none of them are available. QuickCheck-2.1 was excluded because happstack-util-0.4.1 requires QuickCheck <2 QuickCheck-2.1.0.1 was excluded because happstack-util-0.4.1 requires QuickCheck <2 QuickCheck-2.1.0.2 was excluded because happstack-util-0.4.1 requires QuickCheck <2 QuickCheck-2.1.0.3 was excluded because happstack-util-0.4.1 requires QuickCheck <2 Can't cabal handle several versions of the same library in parallel ? If not, how can I solve this problem ? cheers tom

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Iteratee, parsec & co.
by Maciej Piechotka 09 Feb '10

09 Feb '10

I read a lot about iteratee IO and it seemed very interesting (Unfortunately it lacks tutorial). Especially features like 'no input yet' in network programming (with lazy IO + parsec I run into problems as it tried to evaluate the first response character before sending output). I decided first write a simple program and then attempt write a Stream implementation for parsec. > {-# LANGUAGE FlexibleInstances #-} > {-# LANGUAGE MultiParamTypeClasses #-} > import Data.Iteratee > import Text.Parse > > data Buffer a = Buffer > instance Monad m => Stream (Buffer a) (IterateeG [] a m) a where > uncons Buffer = IterateeG loop > where loop (Chunk []) = > return $! Cont (IterateeG loop) Nothing > loop (Chunk (x:xs)) = > return $! Done (Just (x, Buffer)) > (Chunk xs) > loop (EOF Nothing) = > return $! Done Nothing (EOF Nothing) > loop (EOF (Just e)) = > return $! throwErr e 1. I'm not quite sure what Cursor was suppose to do from A Parsing Trifecta presentation. 2. Is there any package which contains this stream definition? 3. Why Seek FileOffset is error message? Regards PS. I guess iteratee does qualify as cafe but if beginner would be more appropriate group then I'm sorry - I'll remember next time.

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haskelldb in-memory driver?
by Johannes Waldmann 09 Feb '10

09 Feb '10

Is there a haskelldb-driver that works with a datasource that is in memory, as a Haskell object? (like LINQ can work on C# collections) - J.

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Compiling on Windows - using a particular Manifest file
by Günther Schmidt 09 Feb '10

09 Feb '10

Hi, how can I make ghc use a particular manifest file for embedding? (on Windows) Günther

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cannot post to haskellmode-emacs@projects.haskell.org
by Jose A. Ortega Ruiz 09 Feb '10

09 Feb '10

Hi, all my posts to the haskellmode-emacs list (using the address in the subject) are being rejected with the error: 451 451 Temporary local problem - please try later (state 18) (after several retries by the Google smtp server, which i use as a smarthost). Any idea of what could be causing this problem? Thanks! jao -- There are two ways to write error-free programs; only the third one works. - Alan Perlis, Epigrams in Programing

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Using ShowS or Difference Lists
by Mark Spezzano 08 Feb '10

08 Feb '10

Hi, Just wondering whether I can use ShowS or tupling or Difference Lists to speed up the following code? It's basic text processing. It takes in a list of Lines where each Line is a list of Words and intersperses " " between them then concatenates them into a longer String. Note that there is a recursive call and the ++ operator. Thanks Mark -- Function: joinLines -- Joins the Words within Lines together with whitespace and newline characters -- Argument: Lines to pad with whitespace and newlines -- Evaluate: The processed and concatenated String joinLines :: [Line] -> String joinLines (l:[]) = concat (intersperse " " l) joinLines (l:ls) = (concat (intersperse " " l)) ++ ('\n':joinLines ls)

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Links to darcs.haskel.org in the haskellwiki
by Henk-Jan van Tuyl 08 Feb '10

08 Feb '10

L.S., There are a lot of links in the haskellwiki that point to projects at darcs.haskel.org; I hope that anyone who moves a project, looks the links up and updates them. An example of a page with several obsolete links is http://www.haskell.org/haskellwiki/Applications_and_libraries/Web_programmi… Validity of links can automatically be checked with the linkchecker: http://validator.w3.org/checklink I have done quite a lot of updating of links in the past, I hope more people are willing to check and update pages that haven't been touched for a while. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html --

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Spelling checker exercise
by Matthew Phillips 08 Feb '10

08 Feb '10

Hello all, sorry to bring up an old chestnut, but I’m trying to improve my Haskell-fu by writing a small program, and chose Peter Norvig’s spelling checker as my exercise material (http://norvig.com/spell-correct.html) While I’ve gotten it working, and found it quite illuminating, I also found it to to be very slow. And then I discovered that, of course, others have been here well before me ([1] and [2]). Those discussions were very interesting, but the code they refer to is mostly not available, so the most I’ve gotten out of it so far is that: (a) I should be using strict left folds and strict Map insertions for the word frequency map (this shaved off about a second: ~5s -> ~4s for a single word on my 2.4GHz MacBook Pro, GHC 6.10.4) (b) I should probably be using ByteString’s (c) Using Set’s for the edit permutations probably isn’t worth it (although I found using plain lists made it about a second slower) (b) is difficult because I’ve used matching patterns plus list comprehensions to generate the potential edits, and I really like how elegantly it pans out that way. Because ByteString’s are not lists, I can’t see a way to keep the current structure and use them. The code is at [3] (link to version at time of post). Profiling [4] shows: $ ./spelling becuase +RTS -p becuase -> because $ cat spelling.prof total time = 4.02 secs (201 ticks @ 20 ms) total alloc = 1,544,257,792 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc train Main 52.7 19.7 readFile Main 28.9 8.6 wordsBy Main 10.9 49.5 toLower Main 7.0 21.8 ... So it appears that “train" (building the freq map) and “readFile” in “nwords" are the places to hone. I will look at using Bloom Filters or Trie’s instead of Data.Map, but I wonder if readFile should be taking nearly %30 of the run time, even for a 6MB file? Sorry to dump such a long post on the list — I’ll understand if no one can be bothered rehashing this. But, in summary I’d like to know: (a) how could I use ByteString’s for this to speed up I/O and reduce memory usage without losing the nice readability? (b) should readFile be so slow? (c) any other tips Possibly all my questions could be answered if someone has the code from the old posts. Cheers, Matthew. [1]: http://haskell.markmail.org/search/?q=norvig%20spelling#query:norvig%20spel… [2]: http://thread.gmane.org/gmane.comp.lang.haskell.cafe/21780 [3]: http://github.com/scramjet/spelling/blob/44fd336ef4f62d49c7087dbc1ffb9c009b… [4]: http://github.com/scramjet/spelling/blob/f5146b24b77443c22975ff69fb91aa922c…

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Interpreting profiling results
by Gregory Collins 08 Feb '10

08 Feb '10

Hello all, A friend and I are trying to benchmark some network server code which runs fine on my OSX laptop (~7500 req/s) but which is >10x slower on a much faster 8-core Xeon Linux box. The profiling run on Linux looks like this: individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 1 0 95.7 0.2 100.0 100.0 ... How should we interpret this result? MAIN doesn't seem to correspond to any user code so we're wondering where the time is going. G. -- Gregory Collins <greg(a)gregorycollins.net>

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