- Glasgow-haskell-users

:def and ghci command output
by Claus Reinke 31 Aug '07

31 Aug '07

ghci's :def takes a 'String -> IO String' and converts it into a ghci command. this makes it possible to pass a command parameter to a haskell function, and to interpret the result of the call as a ghci command. that is nice, but how do i get access to the command's output? that is, i'd like to run a ghci command, and capture its ouput as a haskell String, eg, to pass it on to another ghci command, or to a haskell function. perhaps something simple, like an additional ghci top-level binding: GHCi.cmd :: String -> IO String so that i could write things like let doSomething output = .. :def mymodules \_->GHCi.cmd ":show modules" >>= doSomething or a way to compose ghci commands, so that i could write :def doSomething \output->.. :def mymodules \_->return ":show modules :>>= :doSomething" would that be difficult to provide? claus

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Derived instances
by Fernand 31 Aug '07

31 Aug '07

Hi, I have just discovered Generics in Haskell and, writing some code with GHC, I wondered about the portability of my code. It is possible I overlooked something in the GHC documentation but I did not found a way to obtain, let say, the haskell code for the derived classes. I mean, having the following type declaration : > data Something = This | That deriving (Eq, Ord, Typeable, Data) I can use the -fgenerics to automatically derive instances for Something. But I could wish to have the generated source code for those instances (like, I suppose, the DrIft tool does), for instance, to compile my source with another compiler, which does not support Generics. Is that possible ? Thank you, Fernand

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Re: [Haskell] ghc as a library and profiling
by Simon Marlow 30 Aug '07

30 Aug '07

Sönke Hahn wrote: > I am working on a program that uses ghc as a library to typecheck code. I want > to profile the program (compiling with '-prof -auto-all' and running > with '+RTS -p'). Trying to compile, results in the following message: > > Could not find module `GHC': > Perhaps you haven't installed the profiling libraries for package > ghc-6.6.1? Yes, by default we don't build or supply the GHC package with profiling, because of the extra bloat it would add to the downloads and the time taken to build it. With the latest GHC sources from darcs you can add 'GhcCompilerWays=p' to your mk/build.mk and get the GHC package built for profiling too. > A second idea that comes to my mind is this: > The ghc package is hidden in the standard installation, so i unhided (unhid?) > it via 'ghc-pkg expose ghc'. Maybe it just exposed the non-profiling version > and kept the profiling version hidden? How would i expose both? You probably don't really want to expose the GHC package, because it doesn't use hierarchical modules and so pollutes the top-level module namespace. Cheers, Simon

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template haskell syntax
by Christian Maeder 24 Aug '07

24 Aug '07

Hi, for haskell prime I suggest to change the stolen syntax "[e|", "[p|", "[d|", "[t|" to [|<letter>| in order to avoid the confusion with list comprehensions. Cheers Christian

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Status of GHC runtime dependency on GNU multi precision arithmetic library
by Brian Hulley 22 Aug '07

22 Aug '07

Hi, I know this is a sensitive issue and I absolutely don't want to start any kind of discussion about the merits or otherwise of LGPL, but I was wondering if there are any plans to remove the GNU mp library from the runtime so that it would be possible to distribute native executables compiled with GHC without having to deal with the additional issues raised by the current inclusion of this LGPL component in the runtime. (Afaik everything else in ghc is under a BSD3 license.) It's less of an issue on Linux where libgmp is dynamically linked but when thinking about using Haskell ghc for creating Windows apps it is for me a real problem, because it would mean I'd have to distribute the code for my app as a library along with the code as an executable, thus doubling the download size for my apps as well as having to include a license that has to explain to a possibly non-technical user that although the program includes code that is libre/gratis free the program is not itself free etc etc... Regards, Brian.

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Re: Qualified identifiers opinion
by Christian Maeder 21 Aug '07

21 Aug '07

Hi Isaac, just to give you a reply at all, see below. I reply glasgow-haskell-users(a)haskell.org since I'm not subscribed to haskell-prime. And I don't want to subscribe, because I'm more interested that Haskell becomes more stable (and standard). So here is my opinion: 1. The lexer should recognize keywords. 2. I would not mind if Haskel98 rejected all keywords that are also rejected by extensions, so that the lexer is extension independent. (Starting with Haskell98, removing conflicting identifiers as soon as I switch on valuable extensions does not make sense.) 3. I'm against qualified identifiers, with the unqualified part being a keyword like "Foo.where". (The choice of qualification should be left to the user, usually one is not forced to used qualified names.) 4. However, "Foo.where" should always be rejected and not changed to "Foo.wher e"! (Longest matching, aka "maximal munch", must not consider keywords!) (see end of: http://www.haskell.org/onlinelibrary/lexemes.html#sect2.4) I would not mind if a name "F. " is plainly rejected. It only makes sense, when a data constructor is the first argument of the composition operator "(.)" Maybe "." and "$" as operators should require white spaces on both sides, since "$(" also indicates template haskell. Cheers Christian Isaac Dupree wrote: > > Especially after writing a partial lexer for Haskell, I opine that this > should be all legal: > > > > module Foo where > > --in case you didn't know, this is legal syntax: > Foo.f = undefined > > Foo.mdo = undefined > Foo.where = undefined > x Foo.! y = undefined > x Foo... y = undefined --remember ".." is reserved id, e.g. [2..5] > > > {-# LANGUAGE RecursiveDo, BangPatterns #-} module Bar where > import Foo > hello !x = mdo { y <- Foo.mdo Foo... ({-Foo.-}f x y); return y } > > {- Haskell 98 -} module Baz where > import Foo > goodbye x = x ! 12 > > > > (Foo.where) lexing as (Foo.wher e) or (Foo . where) does not make me > happy. (being a lexer error is a little less bad...) Especially not > when the set of keywords is flexible. I don't see any good reason to > forbid declaring keywords as identifiers/operators, since it is > completely unambiguous, removes an extension-dependence from the lexer > and simplifies it (at least the mental lexer); Also I hear that the > Haskell98 lexing is (Foo.wher e), which I'm sure no one relies on... > > Well, that's my humble opinion on what should go into Haskell' on this > issue. > > Isaac

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[GHC-as-a-library]getModuleInfo: instances for package module unimplemented
by kenny lu 21 Aug '07

21 Aug '07

Hi all, We've been using to GHC-as-a-library to implement some parts of our project. Our goal is to use ghc to extract necessary type information from Haskell modules. Everything works fine until we attempt to collect the declared type class instances from a packaged haskell module, like List, Monad, etc. The program terminates with an error as follows, getModuleInfo: instances for package module unimplemented We manually trace into the source file /ghc/compiler/main/GHC.hs and find the following snipet of code: getPackageModuleInfo :: HscEnv -> Module -> IO (Maybe ModuleInfo) getPackageModuleInfo hsc_env mdl = do #ifdef GHCI (_msgs, mb_avails) <- getModuleExports hsc_env mdl case mb_avails of Nothing -> return Nothing Just avails -> do eps <- readIORef (hsc_EPS hsc_env) let names = availsToNameSet avails pte = eps_PTE eps tys = [ ty | name <- concatMap availNames avails, Just ty <- [lookupTypeEnv pte name] ] -- return (Just (ModuleInfo { minf_type_env = mkTypeEnv tys, minf_exports = names, minf_rdr_env = Just $! nameSetToGlobalRdrEnv names (moduleName mdl), minf_instances = error "getModuleInfo: instances for package module unimplemented", minf_modBreaks = emptyModBreaks })) It is clearly that the field mind_instances is not assigned to a proper value. Can someone kindly advise on how to implement the missing bit? Or pointing out a workaround? Thank you very much. Best Regards, Kenny Zhuo Ming Lu

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wondering about -ddump-parsed, rn
by Isaac Dupree 20 Aug '07

20 Aug '07

Is ghc -ddump-parsed supposed to give parse-syntactically valid Haskell? It nearly does - the only way I've seen it not do so is infix type-signatures and some infix definitions. Answer: no, look at what it does to the operators with fixities. But, -ddump-rn seems better... file: (@@@) :: a a @@@ b = a + b : a + b ==================== Parser ==================== @@@ :: a @@@ a b = ((a + b) : a) + b ==================== Renamer ==================== @@@ :: a @@@ a b = (a + b) : (a + b) It would be interesting if that was a source-to-source transformation on Haskell: a way to delete all the comments and formatting of the original file. Putting parentheses around infix used as prefix would be nice. Of course... the renamer output depends on other modules, and must for the precise reason of imported fixity declarations! GHC isn't trying to do this so I really have no reason to ask it to :) P.S. this (-ddump-) is a nice way to see how some stages of GHC's processing are done, to get to know them a little, I think, after also looking through some code and Commentary Isaac

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Re: Visual Haskell will not Install with Visual Studio 2005, Express Edition
by Duncan Coutts 20 Aug '07

20 Aug '07

On Thu, 2007-07-26 at 23:51 -0700, Sean Johnson wrote: > Hi Everyone, > > Is there some way to install Visual Haskell with VS2005, Express? > Perhaps some workaround or hack? I believe that free version of VS is specifically designed not to allow any plugins, you have to pay for the the full version for that sadly. As a free alternative, emacs and eclipse have Haskell modes and many other editors have Haskell syntax highlighting. Duncan

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where to take ghc-6.8(.1)
by Serge D. Mechveliani 19 Aug '07

19 Aug '07

Yan Linah wrote about testing ghc-6.8(.1). Please, where to take its source from? If it is CVS, then, please, specify the command. Is it with profiling? ----------------- Serge Mechveliani mechvel(a)botik.ru

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