- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] GHC wish
by Christophe Poucet 24 May '06

24 May '06

Hello Chris, It seems that your reply only replied to me and not to the haskell-cafe list. I hope you do not mind that I reply to the list. Anyways, regarding how the AST is pretty printed. I was not thinking of any highlevel pretty printing of an AST (at least not derived automatically). The type of pretty printing I was thinking of would be synonymous to what deriving Show would give you for any type, except that it would be layed out a bit more cleanly with indentation and newlines. Here is an example: data Foo = Foo {unFoo :: [Bar]} data Bar = Bar {unBar :: Int} prettyPrint . Foo. map Bar $ [1..10] Foo { unFoo = [ Bar {unBar = 1}, Bar {unBar = 2}, .. Bar {unBar =10} ] } Jared: Thank you for mentioning DrIFT. Will certainly take a look at it :) Cheers, Christophe Christopher Brown wrote: > Christophe, > > But that depends on what you think is the correct way of displaying > an AST. I can personally think of a few ways an AST could be pretty > printed. > > Chris. > > > On 24 May 2006, at 00:05, Christophe Poucet wrote: > >> Dear all, >> >> I recently stumbled upon something that I think should be added to >> the GHC wishlist. Not knowing where to put it, I will put it here. >> As there is deriving(Show) for most basic data types, wouldn't it be >> possible to have something similar but then deriving(Pretty). When >> printing ASTs it could make it much easier to look at the output. >> >> With regards, >> Christophe >> >> -- >> Christophe Poucet >> Ph.D. Student >> Phone:+32 16 28 87 20 >> E-mail: Christophe (dot) Poucet (at) imec (dot) be >> Website: http://notvincenz.com/ IMEC vzw – Register of Legal >> Entities Leuven VAT BE 0425.260.668 – Kapeldreef 75, B-3001 Leuven, >> Belgium – www.imec.be >> *****DISCLAIMER***** >> This e-mail and/or its attachments may contain confidential >> information. It is intended solely for the intended addressee(s). >> Any use of the information contained herein by other persons is >> prohibited. IMEC vzw does not accept any liability for the contents >> of this e-mail and/or its attachments. >> ********** >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe > > > -- Christophe Poucet Ph.D. Student Phone:+32 16 28 87 20 E-mail: Christophe (dot) Poucet (at) imec (dot) be Website: http://notvincenz.com/ IMEC vzw – Register of Legal Entities Leuven VAT BE 0425.260.668 – Kapeldreef 75, B-3001 Leuven, Belgium – www.imec.be *****DISCLAIMER***** This e-mail and/or its attachments may contain confidential information. It is intended solely for the intended addressee(s). Any use of the information contained herein by other persons is prohibited. IMEC vzw does not accept any liability for the contents of this e-mail and/or its attachments. **********

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Re: [Haskell-cafe] GHC wish
by Jared Updike 23 May '06

23 May '06

Sorry, meant to reply all: --------------------------------------------------- This tool (DrIFT) can derive these instances for you, if you care to make rules for it, for Pretty: http://repetae.net/john/computer/haskell/DrIFT/ Jared. -- http://www.updike.org/~jared/ reverse ")-:"

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Problem trying to get class Bounded to work
by Brian Hulley 23 May '06

23 May '06

Hi - I've got the following function which doesn't compile: createMonoMultiFont :: (MonadException m, Enum i, Bounded i) => [(i, Font, Colour)] -> m (MonoMultiFont i) createMonoMultiFont elements = liftIO . block $ do mmfRaw <- duma_MonoMultiFont_create (fromEnum (maxBound::i)) mmfPtr <- newForeignPtr duma_MonoMultiFont_Release mmfRaw return $ MonoMultiFont mmfPtr The problem is that ghc complains that there is no instance for Bounded i even though I've written "Bounded i" in the type declaration for the function. I was expecting that I could use the same type variables in the function body as in the type signature so that I could use maxBound::i to find the max bound of whatever type is instantiated to i. What am I doing wrong here, and is it possible to create such a function? Thanks, Brian.

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calling haskell from C++
by Vladimir Portnykh 23 May '06

23 May '06

Hello ALL, I am very new to Haskell and my question might appear very basic sorry about it in advance. I have a C++ application and I would like to be able to launch Haskell interpreter (lets say GHC) supplying the Haskell code (in a file ) to be interpreted from it. The Haskell program generates some output and I would like to use this output in my C++ program. Do you have any simple example to help me, please? Many thanks, Vladimir _________________________________________________________________ Are you using the latest version of MSN Messenger? Download MSN Messenger 7.5 today! http://join.msn.com/messenger/overview

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Trouble with Cabal
by Scherrer, Chad 22 May '06

22 May '06

Thanks to all who responded about the benefits of using Cabal. After trying out Bulat's Streams library, I thought I would download ByteString (aka FPS) to compare the wc demos. To compile something using Streams, I need to use a -i flag (thanks Bulat). When I followed the README that comes with ByteString, I get this: % ./Setup.hs install Installing: /f/g/lib/fps-0.7 & /f/g/bin fps-0.7... *** Exception: /f: createDirectory: permission denied (Permission denied) I don't have root on this machine, and it's not obvious (to me) how to specify that everything should be installed locally. Any suggestions? Thanks, Chad Scherrer Computational Mathematics Group Pacific Northwest National Laboratory "Time flies like an arrow; fruit flies like a banana." -- Groucho Marx

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QuickCheck Fun with Phantom Types
by Dominic Steinitz 22 May '06

22 May '06

I was doing Exercise 5 of Ralf's Fun with Phantom Types and naturally thought I'd check my solution with QuickCheck. The best I could was this. Is there something better? Can you somehow generate random types as well as random values in those types? Thanks, Dominic. PS the full source for my solution with tests is attached. prop_Idem t x = x == uncompress t (compress t x) instance Arbitrary Char where arbitrary = oneof (map return ['A'..'z']) class Reflect a where reflect :: Type a instance Reflect Int where reflect = RInt instance Reflect Char where reflect = RChar instance (Reflect a, Reflect b) => Reflect (a,b) where reflect = RPair reflect reflect instance Reflect a => Reflect [a] where reflect = RList reflect type Test1 = Int -> Bool type Test2 = (Int,Int) -> Bool type Test3 = String -> Bool type Test4 = (String,String) -> Bool main = do quickCheck ((prop_Idem reflect) :: Test1) quickCheck ((prop_Idem reflect) :: Test2) quickCheck ((prop_Idem reflect) :: Test3) quickCheck ((prop_Idem reflect) :: Test4)

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Re: Writing an extensible interpreter
by Jonathan Tang 22 May '06

22 May '06

> Message: 2 > From: "David House" <dmhouse(a)gmail.com> > Subject: [Haskell-cafe] Writing an extensible interpreter > I'm in the process of writing an interpreter for the self-modifying > automaton languages SMATINY [1], designed by ihope (whose name some of > you may recognise from IRC). The current effort is online [2], but > it's at a rather early stage and there's a few modifications I'd like > to make to it. [snip] However, the remaining issue is step 1): how would the metacode handle > additional constructors to the Step ADT? Type classes won't work here: > the intepreter has a type of [Step] -> String. With type classes this > would have a type of something like Step a => [a] -> String, but by > the homogeneity of lists you'd only be able to have one type of step > in your program. > > You can get around the homogeneity of lists problem with existential types: http://www.haskell.org/hawiki/ExistentialTypes http://halogen.note.amherst.edu/~jdtang/scheme_in_48/tutorial/evaluator2.ht… Another solution might be to eliminate the algebraic data type entirely and have the Parsec actions return a Smatiny action. Instead of dispatching on the constructor of Step, package up any information you need as a closure and make Step a type synonym for 'Smatiny ()' or 'Smatiny a' or whatever type you need. Then the interpreter main loop just executes the action returned by the parser. - Jonathan

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Writing an extensible interpreter
by David House 22 May '06

22 May '06

Hi all. I'm in the process of writing an interpreter for the self-modifying automaton languages SMATINY [1], designed by ihope (whose name some of you may recognise from IRC). The current effort is online [2], but it's at a rather early stage and there's a few modifications I'd like to make to it. To begin with, extensibility is key. Such tiny languages are designed to be easily extendable, and I'd like my interpreter to follow suit. At the moment, adding a new command is as follows: 1) Add a new constructor for the Step type to represent your command. 2) Write a Parsec parser for your command in Smatiny.hs. 3) Add said parser to the 'inputs' list in Smatiny.hs. 4) Write a 'handler' for your command; a function in State that will take the appropriate action. This is a bit of an ordeal; I'd like new commands to be addable without touching Smatiny.hs, which will form the base of the interpreter. One solution I was thinking about was to write a new module for each command that exports a "parser" and "handler" function. A bit of metacode would read the Commands directory then import qualified all the modules it finds in there. Subsequently, it would call parseSmatiny (the parser; in Smatiny.hs) with all the parsers it found as an argument, then send the output of this into runSmatiny (the interpreter; also in Smatiny.hs). However, the remaining issue is step 1): how would the metacode handle additional constructors to the Step ADT? Type classes won't work here: the intepreter has a type of [Step] -> String. With type classes this would have a type of something like Step a => [a] -> String, but by the homogeneity of lists you'd only be able to have one type of step in your program. Thanks in advance for your input. Let me know if I didn't explain something too well; I have a tendancy toward brevity :) [1]: http://esoteric.voxelperfect.net/wiki/SMATINY [2]: http://esoteric.voxelperfect.net/files/smatiny/impl/smatiny.tar.gz -- -David House, dmhouse(a)gmail.com

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parsing machine-generated natural text
by Evan Martin 21 May '06

21 May '06

For a toy project I want to parse the output of a program. The program runs on someone else's machine and mails me the results, so I only have access to the output it generates, Unfortunately, the output is intended to be human-readable, and this makes parsing it a bit of a pain. Here are some sample lines from its output: France: Army Marseilles SUPPORT Army Paris -> Burgundy. Russia: Fleet St Petersburg (south coast) -> Gulf of Bothnia. England: 4 Supply centers, 3 Units: Builds 1 unit. The next phase of 'dip' will be Movement for Fall of 1901. I've been using Parsec and it's felt rather complicated. For example, a "location" is a series of words and possibly parenthesis, except if the word is SUPPORT. And that "Supply centers" line ends up being code filled with stuff lie "char ':'; skipMany space". I actually have a separate parser that's Javascript with a bunch of regular expressions and it's far shorter than my Haskell one, which makes sense as munging this sort of text feels to me more like a regexp job than a careful parsing job. I'm considering writing a preprocessing stage in Ruby or Perl that munges those output lines into something a bit more "machine-readable", but before I did that I thought I'd ask here if anyone had any pointers, hints, or better ideas.

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Re: [Haskell] installing streams library
by Chad Scherrer 19 May '06

19 May '06

Thanks Jared, but already tried those. I was able to download the Streams library, but I have know idea how to install it. On 5/19/06, Jared Updike <jupdike(a)gmail.com> wrote: > > I found this in an old post (gotta love GMail search): > > > You can find further information about the library at the > > page http://haskell.org/haskellwiki/Library/Streams and > > download it as http://freearc.narod.ru/Streams.tar.gz > > from a thread in February entitled: > > Streams: the extensible I/O library (Feb 21) > > Google site:haskell.org bulat extensible I/O library for the thread, etc. > > Hope that helps, > Jared. > > On 5/19/06, Chad Scherrer <chad.scherrer(a)gmail.com> wrote: > > It sounds like Bulat has gotten some impressive I/O speedups with his > > Streams library. I'd like to try this out, but I'm having some trouble > > installing it. I'm using GHC on Linux. > > > > My first attempt was looking around on this page: > > http://www.haskell.org/haskellwiki/Library/Streams > > > > There's a really nice description, but no signs of where to actually get > the > > library. Eventually (thanks to Google) I tracked down this message: > > http://article.gmane.org/gmane.comp.lang.haskell.general/13625 > > > > From here I was able to download it, but there's no information > regarding > > how this needs to be set up. There are directories "Data", "Examples", > and > > "System", which I assume are supposed to be plugged into the > hierarchical > > module structure, but how do I do that? I thought this might have > something > > to do with Cabal (I've not yet used that), but the Cabal manual talks > about > > a .cabal file, which doesn't exist here. > > > > Does this follow some standard approach that I'm not familiar with? > Where > > should I look to learn more? > > > > Thanks, > > -- > > > > Chad Scherrer > > > > "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx > > _______________________________________________ > > Haskell mailing list > > Haskell(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell > > > > > > > > > -- > http://www.updike.org/~jared/ > reverse ")-:" > -- Chad Scherrer "Time flies like an arrow; fruit flies like a banana" -- Groucho Marx

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