- Haskell-Cafe - Haskell.org

Shootout favoring imperative code
by Scherrer, Chad 11 Jan '06

11 Jan '06

Several people on this list have said that the shootout favors imperative code. Is this really the case? Why is it Clean seems to have no trouble (for the incomplete set of benchmarks that are written in it)? http://shootout.alioth.debian.org/clean.php How difficult would it be to translate the Clean algorithms into Haskell? -Chad

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Intersection types for Haskell?
by Brian Hulley 11 Jan '06

11 Jan '06

Hi - I'm wondering if there is any possiblility of getting intersection types into Haskell. For example, at the moment there is no (proper) typing for: f g x y = (g x, g y) Ideally, I'd like to be able to write: f:: (a -> b & c -> d) -> a -> c -> (b,d) or f :: (a -> b a) -> c -> d -> (b c, b d) which is perhaps clearer and prevents bad types such as (Int -> String & Int -> Char) by construction. While it may be impossible (?) to infer such a type for f, would it be possible to make use of such an annotation (esp since Haskell with GHC extensions already has arbitary rank polymorphism)? Also, as a second point, could functional dependencies in type classes be written using a similar syntax eg instead of class Insert t c a | c a -> t where insert :: t -> c a -> c a we could write: class Insert (h (c a)) c a where insert :: h (c a) -> c a -> c a or class Insert t@(h (c a)) c a where -- re-using as-pattern syntax insert :: t -> c a -> c a to avoid having to have a special syntax just for functional dependencies and/or to be able to write more complicated fundeps more succinctly? Regards, Brian Hulley

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FunctionalJ - a library for Functional Programming in Java
by Graham Klyne 11 Jan '06

11 Jan '06

A colleague alerted me to this, which I thought might be of interest here: http://www.theserverside.com/news/thread.tss?thread_id=38430 (I have already found that my Haskell experiences have influenced my Python programming; maybe there's also hope for my Java?) #g -- Graham Klyne For email: http://www.ninebynine.org/#Contact

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rank-2 :(
by Bulat Ziganshin 10 Jan '06

10 Jan '06

Hello , those rank-2 types wil make me mad :) encodeHelper :: (MRef m r, Binary m a, BitStream m (StringBuffer m r)) => a -> m String encodeHelper x = do h <- newStringBuffer "" stringBufferDefaultCloseFunc put_ h x getStringBuffer h encode x = runST (encodeHelper x) i can't force `encode` to compile, either with or without any type signatures. actually, signature for `encodeHelper` was developed by Hugs, but now i don't know how to proceed further just now tried to force Hugs tell me its type. mission impossible :) DataAltBinaryClass> :t (runST (encodeHelper 1)) ERROR - Cannot justify constraints in application *** Expression : encodeHelper 1 *** Type : ST c [Char] *** Given context : () *** Constraints : (Num b, Binary (ST c) b) Binary class in my library includes monad in its header. May be it's the cause of problems? class Binary m a where -- | Convert value to sequence of bits and write it to the stream put_ :: (BitStream m h) => h -> a -> m () but it's needed because MArray types, for example, can be serialized only in the appropriate monad: instance Binary IO (IOArray a) where ... -- Best regards, Bulat mailto:bulatz@HotPOP.com

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Fannkuch timings
by Daniel Fischer 10 Jan '06

10 Jan '06

On my 1.2 GHz Duron (SuSE linux), I get significantly different timings than those on the wiki. Sebastian Sylvan's, Kimberley Burchett's and Bertram Felgenhauer's all take roughly thrice as long as posted (that's rather consistent, but the factor is surprisingly large). Cale Gibbard's takes 18.44 secs for N = 9, which is rather bad, I think. Really surprising (to me) are the following (N = 10) Algo Wiki Here Clean imperative 2.1 s 4.54 s Fastest Pure 1.8 s 8.65 s Fastest Impure 1.4 s 1.77 s. So the ratio for the fast impure version is approximately 1.6GHz/1.2GHz, which is natural, but the ratio for clean impure is 2.2 and for the fast pure version, it's even 4.8! All are compiled with -O2 -optc-O3. Does that mean my system is really poor in producing binaries from pure Haskell? And why would that be so? Cheers, Daniel

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hPutStrLn and hFlush
by Gracjan Polak 10 Jan '06

10 Jan '06

Hi all, A bit strange behaviour with hPutStrLn. Consider following program: main = do handle <- openFile "output.txt" WriteMode hPutStrLn handle (unlines contLines2) -- hFlush houtput where contLines2 = flip map [1..2000] $ \x -> show x ++ " been there done that" Outputs file which ends with following lines: 1989 been there done that 1990 been there done that 1991 been there done that 1992 been there done that 199 (END) So the output is truncated. When I uncomment hFlush, file is fully written. Is this expected/documented behaviour? Platform: WinXP, GHC version 6.4.1 -- Regards, Gracjan

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In for a penny, in for a pound.
by David F. Place 10 Jan '06

10 Jan '06

Hi All, Regarding the Fannkuch Shootout Entry: If we are willing to specialize flop in the way shown on the wiki, another 8% can be gained by similarly specializing rotate: rotate 2 (x1:x2:xs) = x2:x1:xs rotate 3 (x1:x2:x3:xs) = x2:x3:x1:xs rotate 4 (x1:x2:x3:x4:xs) = x2:x3:x4:x1:xs rotate 5 (x1:x2:x3:x4:x5:xs) = x2:x3:x4:x5:x1:xs rotate 6 (x1:x2:x3:x4:x5:x:6:xs) = x2:x3:x4:x5:x:6:x1:xs rotate 7 (x1:x2:x3:x4:x5:x:6:x7:xs) = x2:x3:x4:x5:x:6:x7:x1:xs rotate 8 (x1:x2:x3:x4:x5:x:6:x7:x8:xs) = x2:x3:x4:x5:x:6:x7:x8:x1:xs rotate 9 (x1:x2:x3:x4:x5:x:6:x7:x8:x9:xs) = x2:x3:x4:x5:x: 6:x7:x8:x9:x1:xs rotate 10 (x1:x2:x3:x4:x5:x:6:x7:x8:x9:x10:xs) = x2:x3:x4:x5:x: 6:x7:x8:x9:x10:x1:xs rotate n (x:xs) = rot' n xs where rot' 1 xs = x:xs rot' n (x:xs) = x:rot' (n-1) xs Cheers, David -------------------------------- David F. Place mailto:d@vidplace.com

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Re: [Haskell-cafe] Intersection types for Haskell?
by Brian Hulley 10 Jan '06

10 Jan '06

José Miguel Vilaça wrote: > Hi > > If I understand your problem than the following is a solution: > > -------------------------------------------------- > > {-# OPTIONS -fglasgow-exts #-} > > class Foo a b where > g :: a -> b > > type A = {- change the following -} Int > type B = {- change the following -} Char > > instance Foo A B where > g a = {- change the following -} ' ' > > type C = {- change the following -} Float > type D = {- change the following -} String > > instance Foo C D where > g c = {- change the following -} "" > > > f :: (Foo a b, Foo c d) => a -> c -> (b, d) > f x y = (g x, g y) Thanks for the workaround. However this does not seem to be quite so general as intersection types, because it would only allow me to define f for some specific g ie the g of Foo, rather than for any general function... Regards, Brian Hulley

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RE: [Haskell] Haskell DB bindings (was Re: ANN: HDBC (HaskellDatabase Connectivity)
by Bayley, Alistair 10 Jan '06

10 Jan '06

[Moving to café, too] > There are three active database libraries: HDBC, HSQL and Takusen. It > is quite disappointing from my point of view. Recently there was the > same situation with the GUI libraires. The Haskell Community is quite > small to waste efforts, developing different libraries for the same > things. When I started with HSQL there were only two database > libraries: HaSQL for ODBC and libpq for PostgreSQL. They both are > dead, I think. I decided that it is useful to have one abstract API > that can cover all database bindings. I imagine something like JDBC, > ADO or DBI for Haskell. If you guys would like this to happen then > lets discuss what we want. I would be happy to work on single project > that can satisfy all needs. > > Cheers, > Krasimir > ... The Haskell Community is quite > small to waste efforts, developing different libraries for the same > things. Yes, that could be considered undesirable. However, there is the choice for users over which API to choose that best supports their needs. In the use of an enumerator, Takusen has chosen quite a different design space from HSQL and HDBC. Whether or not that proves to be a good idea, or attractive to users, remains to be seen :-) HaskellDB+HSQL seems to be to be the most mature, and actively maintained. Although I'm keen to progress Takusen, I find it hard at present to take the necessary time, so work seems to stall. I'd have no bone to pick with HaskellDB+HSQL being promoted as the default database API, but I still want to work on Takusen, because I think there are some ideas worth exploring. When I started Takusen, I was specifically interested in using HaskellDB to interface to Oracle. At the time, HaskellDB did not use HSQL, and HSQL lacked a unifying interface, so I started work on a low-level library to Oracle (I was also keen to learn to use the FFI). The design later evolved towards the enumerator approach (Oleg persuaded me that it was a good idea) and the HaskellDB goal was never reached. Now that HSQL supports Oracle, I can choose to use HaskellDB with Oracle, so I suppose my original goal has been satisfied. Alistair ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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RE: Re[2]: [Haskell-cafe] I/O and utf8
by Bayley, Alistair 10 Jan '06

10 Jan '06

> From: haskell-cafe-bounces(a)haskell.org > [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Bulat Ziganshin > > i have the question about this issue - i also want to provide > autodetection mechanism, which relies on first bytes of text files to > set proper encoding. what is the standard rules to encode utf8/utf16 > encoding used for text in file in these first bytes? Are you asking about the byte-order-mark in UTF encodings? http://www.unicode.org/faq/utf_bom.html#BOM Note that UTF8 files typically lack the BOM, as UTF8 is meant to be backwards-compatible with US7ASCII, I think. Windows Notepad is one of the few programs that will insert it if a text file is saved as UTF8. Alistair. ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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