- Glasgow-haskell-users

Type families: module export of instance data constructor
by Ben Horsfall 22 Dec '08

22 Dec '08

I have a type family class Lang term where data Token term :: * : with instance Lang Term where newtype Token Term = T String : I can't work out how to export the type constructor T from the module, unless I make no explict exports from the module at all. Ben

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Re: [Haskell-cafe] Can I build and install GHC 6.10.1 without previous installed ghc
by Don Stewart 22 Dec '08

22 Dec '08

chunye.wang: > Hi All, > > > I have our own Linux distribution installed in my server. > it is based on RedHat 9.0. Because it is the server, I can > not update it to any other linux distribution > > Here is my situation, I have no machine with any version of ghc > installed. Please use a basic linux binary. http://haskell.org/ghc/download_ghc_6_10_1.html#x86linux Such as "Linux (x86)" -- Don

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Can't compile GHC 6.8.2
by Barney Stratford 21 Dec '08

21 Dec '08

I'm trying to compile GHC 6.8.2 using my existing GHC 6.2, but the typechecker refuses to compile. The problem seems to be that the hi-boot files in compiler/typecheck contain some incorrect type signatures. I've fixed most of them, but TcMatches.hi-boot-6 has slightly stumped me. As it stands, it says tcMatchesFun :: Name.Name -> HsExpr.MatchGroup Name.Name -> TcType.BoxyRhoType -> TcRnTypes.TcM (HsBinds.HsWrapper, HsExpr.MatchGroup TcRnTypes.TcId) but it should say something like tcMatchesFun :: Name.Name -> Bool -> HsExpr.MatchGroup Name.Name -> TcType.BoxyRhoType -> TcRnTypes.TcM (HsBinds.HsWrapper, HsExpr.MatchGroup TcRnTypes.TcId) Unfortunately, that doesn't work, as it assumes I meant TcMatches.Bool, so I tried saying Prelude.Bool instead. Now I get the complaint that Prelude.Bool isn't in scope. Has anyone else seen this issue? I've looked for answers in the docs and with Google, but no luck. I'm running Mac OS 10.3, with GHC 6.2 installed under Fink. I borrowed the Fink package for GHC 6.8.2 and adapted it slightly so it would bootstrap from my existing GHC, as the bootstrap code available for download relies on a later version of my OS. GHC 6.2 can't compile GHC 6.10, which is why I'm going for the earlier version. Cheers, Barney.

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Graham Hutton's calculator example for win32
by Ahn, Ki Yung 21 Dec '08

21 Dec '08

In Graham Hutton's "Programming in Haskell" there is an interactive calculator example using ANSI code to implement the UI on the terminal. This example doesn't work on MS Windows XP or other MS OSes based on NT kernel, since their command line does not support ANSI very well. But, thanks to ansi-terminal on Hackage, I was able to extract minimal code from the package to make a win32 version of the calculator example in Hutton's book. calculatorWin32.lhs and Win32ANSI.hs is an implementation for win32. I extracted the win32 console API bindings for setting cursor positions from ansi-terminal project and put them in Win32ANSI.hs. I had to put this in a separate file because I had an issue with ghci. To run this, I had to compile the console API bindings with ghc first and then run ghci as follows C:\> ghc -c Win32ANSI.hs C:\> ghci calculatorWin32.lhs Without compiling the object code, ghci cannot find the proper link for win32 console API FFI bindings. C:\> ghci calculatorWin32.lhs GHCi, version 6.10.1: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer ... linking ... done. Loading package base ... linking ... done. [1 of 3] Compiling Parsing ( Parsing.lhs, interpreted ) [2 of 3] Compiling Win32ANSI ( Win32ANSI.hs, interpreted ) During interactive linking, GHCi couldn't find the following symbol: GetConsoleScreenBufferInfo@8 This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org Is this a bug or a natural behavior of ghci? This is strange to me since ghci finds the proper link for the functions in the other C libraries such as getch in conio.h. In addition, I am attaching a patched calculator.lhs which works for Unix/Linux on both GHC 6.8.x and GHC 6.10.1. The one currently on the book homepage only works for GHC 6.8.x but not GHC 6.10.1. This is due to the bug fix of hSetBuffering in GHC 6.10.1. To run these calculator example you will also need Parsing.lhs from the book hompage. http://www.cs.nott.ac.uk/~gmh/Parsing.lhs -- Ahn, Ki Yung

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please test: cabal install now less eager to reinstall core packages
by Duncan Coutts 19 Dec '08

19 Dec '08

Claus, Simon, You'll recall the cabal-install problem you noticed recently where it decides it wants to re-install some core library like array or containers or whatever. I'd appreciate it if you could test the darcs version of cabal-install and see if it is behaving better now. It was choosing to re-install packages when the way it had chosen to configure the available version of the package (ie what exact dependencies it'd picked) did not exactly match those of the installed package. I've changed things so that it now picks the installed version when the additional constraints it adds (direct and indirect dependencies) do not conflict with the existing constraints. This means it'll pick the installed instance in many more cases and when it does not that there is a more legitimate reason. It still may have been possible to use the installed version if we had known that information much earlier and made different choices at an earlier stage. I've not yet added support for user supplied install constraints but I plan to shortly (eg --constraint='array installed'). Duncan

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type families and overlapping
by Jorge Marques Pelizzoni 17 Dec '08

17 Dec '08

Hi, While playing with type families in GHC 6.10.1, I guess I bumped into the no-overlap restriction. As I couldn't find any examples on that, I include the following (non-compiling) code so as to check with you if that's really the case: ------------------------------------------- {-# OPTIONS -fglasgow-exts #-} {-# LANGUAGE OverlappingInstances #-} {-# LANGUAGE UndecidableInstances #-} module Main where class Expr t where type ExprRslt t :: * eval :: t -> ExprRslt t instance Expr t where type ExprRslt t = t -- overlap? eval = id data Vector a = Vector {width :: !Int, dat :: [a]} data Subscript a = Subscript {vec :: (Vector a), ind :: !Int} instance Expr (Subscript a) where type ExprRslt (Subscript a) = a eval sub = (dat.vec $ sub) !! ind sub ------------------------------------------------ So this means that classes with associated types cannot have default instances at all? If so, could you possibly refer me to any material explaining why? Thanks in advance. Cheers, Jorge.

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Type signature inside an instance declaration
by Kwanghoon Choi 16 Dec '08

16 Dec '08

======================================================================= module Test where class Arg a where pr :: a -> String instance Arg Int where pr _ = "i" instance Arg Char where pr _ = "c" instance Arg a => Arg [a] where pr _ = "[" ++ pr (undefined :: a) ++ "]" -- the type variable 'a' is interpreted as an unbound one. -- (1) pr :: [a] -> String -- (2) pr (_ :: [a]) = "[" ++ pr (undefined :: a) ++ "]" ======================================================================= Dear All, I got some problem when I try to compile the above program. The problem is due to the presence of a type variable 'a' in the body of the last instance declaration. How could I refer to the type variable of Arg [a] in the instance declaration? I tried these options 1) by giving an explicit declaration for pr 2) by giving a type signature to the argument of pr with -XPatternsSignatures The first option gives me back an error : Misplaced type signature: pr :: [a] -> String The type signature must be given where `pr' is declared The second option gives me an error: Test.hs:21:12: Not in scope: type variable `a' Would anybody help me to understand this problem? Thanks in advance. Kwanghoon

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runghc error with glibc 2.8: unknown symbol `fstat64'
by prj＠po.cwru.edu 15 Dec '08

15 Dec '08

I get this error when running a script with runghc, if ghc was built againt glibc 2.8: ghc: /package/host/code.dogmap.org/foreign/ghc-6.10.1+spf+0/prefix/lib/ghc-6.10.1/base-4.0.0.0/HSbase-4.0.0.0.o: unknown symbol `fstat64' ghc: unable to load package `base' With glibc 2.6.1, it works. (At least, ghc 6.8.3 works with glibc 2.6.1. I didn't try ghc 6.10.1 with glibc 2.6.1, but ghc 6.8.3 gives the same error with glibc 2.8, so the ghc version doesn't seem to matter.) The output from "make" when building ghc didn't have any linking errors/warnings related to HSbase, as far as I can see. Has anyone seen anything like this? Any ideas? paul

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ghc-paths
by Jens Petersen 12 Dec '08

12 Dec '08

Are there any plans to include ghc-paths in ghc itself? Jens

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IMCROSS and ghc
by John Meacham 11 Dec '08

11 Dec '08

I was wondering if anyone has gotten ghc to work with IMCROSS[1]. I'm Cross is a way to build native windows and mac osx apps on linux. quite convinient for making distribution packages for those other platforms or if you want to use linux's toolset during your build. basically, IMCROSS installs a couple new gccs with names like /usr/local/bin/i386-mingw-gcc and so forth, is there some way to get ghc to use said non-native compiler as its back end? It seems that ghc will also need to build the libraries with different #define's as well to reflect the target windows or mac environment. [1] http://www.sandroid.org/imcross/ John -- John Meacham - ⑆repetae.net⑆john⑈

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