- Glasgow-haskell-users

scope of header files
by Duncan Coutts 03 Apr '08

03 Apr '08

I was under the impression that with ghc, ffi import declarations like this do not escape the module: foreign import ccall unsafe "foo.h foo" foo :: IO () However it seems that this one does: foreign import ccall unsafe "curses.h & stdscr" stdscrp :: Ptr WINDOWptr from: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mage-1.0 perhapsPbecause it's a pointer import it gets treated differently? Is this correct and expected behaviour? It's hard to tell what header files need to be used globally and inherited by client packages and which can safely be used privately. Duncan

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Confused about typing in ghci
by Patrick Surry 02 Apr '08

02 Apr '08

I'm new to Haskell and functional programming; have been exploring the fixed-point combinator based on the exercise in the HSOE book. Having an odd issue with typing in ghci which I don't understand - maybe it's to do with section 3.4.5. "Type defaulting in GHCi" but I don't really grok that yet... (BTW, an unrelated question: is there a good reference where I can understand the precendence/associativity rules for Haskell? I continually find myself needing lots of parens before expressions behave as I expect, and get very confused trying to use the $ operator - usually resorting to lots of parens again :-) My typing question might boil down to this simple example, though my original example follows: -- Why don't these (particularly g and g') all have the same type? Prelude> :t (\x -> x+1) (\x -> x+1) :: (Num a) => a -> a Prelude> let g = (\x -> x+1) Prelude> :t g g :: Integer -> Integer Prelude> let g' x = x + 1 Prelude> :t g' g' :: (Num a) => a -> a -- Here's my original fixed-point combinator example: Prelude> let fix f = f (fix f) -- here's a silly (but working) implementation of length using fix: Prelude> fix (\g xs -> if xs == [] then 0 else (1 + g (tail xs))) [1,2,3,4] 4 -- so I examine the types of the parts, which seems fine: Prelude> :t fix (\g xs -> if xs == [] then 0 else (1 + g (tail xs))) ... :: (Num t, Eq a) => [a] -> t Prelude> :t (\g xs -> if xs == [] then 0 else (1 + g (tail xs))) ... :: (Num t, Eq a) => ([a] -> t) -> [a] -> t -- but now I try to bind the anonymous function to a name -- this seems to get the types wrong and no longer works as I expect: Prelude> let lenstep = (\g xs -> if xs == [] then 0 else (1 + g (tail xs))) Prelude> :t lenstep lenstep :: ([()] -> Integer) -> [()] -> Integer Prelude> :t fix lenstep fix lenstep :: [()] -> Integer Prelude> let len' = fix (\g xs -> if xs == [] then 0 else (1 + g (tail xs))) Prelude> :t len' len' :: [()] -> Integer Prelude> Prelude> len' [1,2,3,4] <interactive>:1:12: No instance for (Num ()) arising from the literal `4' at <interactive>:1:12 Possible fix: add an instance declaration for (Num ()) In the expression: 4 In the first argument of `len'', namely `[1, 2, 3, 4]' In the expression: len' [1, 2, 3, 4] -- maybe this is just me not understanding name binding properly; it seems to work if I do it this way: Prelude> let lenstep' g xs = (if xs == [] then 0 else (1 + g (tail xs))) Prelude> :t lenstep' lenstep' :: (Eq a, Num t) => ([a] -> t) -> [a] -> t Prelude> :t fix lenstep' fix lenstep' :: (Eq a, Num t) => [a] -> t Prelude> fix lenstep' [1,2,3,4] 4 -- but what's the difference? Cheers, Patrick Patrick.Surry(a)portraitsoftware.com <mailto:Patrick.Surry@portraitsoftware.com> , VP Technology Tel: (617) 457 5230 Mob: (857) 919 1700 Fax: (617) 457 5299 Map <http://maps.google.com/maps?f=q&hl=en&q=125+Summer+St,+Boston,+MA+02110 &ie=UTF8&z=15&ll=42.353153,-71.057296&spn=0.022644,0.054245&om=1&iwloc=A > Portrait Software introduces Portrait Campaign Manager <http://www.portraitsoftware.com/Products/portrait_campaign_manager> : Easy, integrated campaign management for automated and highly targeted outbound marketing http://supportcentre.portraitsoftware.com/Vmail/emailfooter/balloon.gif <http://www.portraitsoftware.com/> http://supportcentre.portraitsoftware.com/Vmail/emailfooter/portrait_sof tware_logo.gif <http://www.portraitsoftware.com/> www.portraitsoftware.com <http://www.portraitsoftware.com/> ________________________________________________________________________ DISCLAIMER: This e-mail is intended only for the addressee named above. As this e-mail may contain confidential or privileged information, if you are not the named addressee, you are not authorised to retain, read, copy or disseminate this message or any part of it. If you received this email in error, please notify the sender and delete the message from your computer.

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ANN: prof2dot, a graphical profiling tool
by Gregory Wright 02 Apr '08

02 Apr '08

I am pleased to announce the first release of prof2dot, a graphical profiling tool for use with GHC. While GHC has in the past worked with graphical profiling tools, they have been heavyweight and/or proprietary. Prof2dot is a simple tool for converting profiling information into a graphical format, released under a BSD3 license. It is simple because it offloads all of the work of rendering the graph onto Graphviz. So you need to install the Graphviz tools in order to use it. The program is a filter that takes the profiling output generated by running a GHC-compiled program with the "+RTS -px -RTS" option and turns it into a dot file. (The "dot" format is a textual representation of a directed or undirected graph.) The dot file can rendered in any format supported by Graphviz's dot program, and the file itself can be post-processed or edited to adjust the layout. Features of prof2dot: * display either the call graph (default) or the call tree, * colorize by cost center count, time or allocations, * group cost centers in the same module. Prof2dot installs as a typical caballized application. Running "prof2dot -?" from the command line will give a short summary of how to use the program and its options. Rendering very large graphs can exceed the internal resource limits of dot. You may have to compile your own version of the Graphviz tools with higher limits to handle these cases. A example of a colorized profile of a medium sized project is shown on our company's web site: http://antiope.com/downloads.html. Click on the small image to download a pdf of the complete profile graph. Prof2dot is available from hackage or the link given above. -Greg

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ghc fails to find the right instance
by Joachim Breitner 01 Apr '08

01 Apr '08

Hi, I was told on #haskell that I should bring this up here, to ask whether this is a bug in ghc6 or otherwise explain this to me. I’m trying to write the function "addd" which takes an arbitrary number of Integer arguments and returns the sum. This code works: -- Try 1 class More a where more ::Integer -> a instance (More a, Integral i) => More (i -> a) where more v1 v2 = more (v1 + toInteger v2) instance More Integer where more v = v addd :: More a => a addd = more 0 printI :: Integer -> IO () printI = print main = do printI $ addd printI $ addd 1 printI $ addd 1 2 printI $ addd 1 2 3 -- SNIP But when I try to use a concret type (Integer) instead of the (Integral i =>) condition (which should make the program more concrete, I’d say) and write the following instance: -- Try 2 (changed lines of code) instance More a => More (Integer -> a) where more v1 v2 = more (v1 + v2) -- SNIP I get this error: test.hs:4:0: Illegal instance declaration for `More (Integer -> a)' (All instance types must be of the form (T a1 ... an) where a1 ... an are distinct type *variables* Use -XFlexibleInstances if you want to disable this.) In the instance declaration for `More (Integer -> a)' Failed, modules loaded: none. Well, I add {-# LANGUAGE FlexibleInstances #-} and get this error for the line "printI $ addd 1" (and similar errors for the other following addd lines): test.hs:19:17: No instance for (More (t -> Integer)) arising from a use of `addd' at test.hs:19:17-22 Possible fix: add an instance declaration for (More (t -> Integer)) In the second argument of `($)', namely `addd 1' In the expression: printI $ addd 1 In a 'do' expression: printI $ addd 1 And this is the point where I’m lost and would like to ask for hints what this means. Thanks, Joachim -- Joachim "nomeata" Breitner mail: mail(a)joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nomeata(a)debian.org

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simple CSE?
by Conal Elliott 01 Apr '08

01 Apr '08

I'd like to know if it's possible to get GHC to perform some simple CSE for function-level programming. Here's a simple example: liftA2 (*) sin sin :: Double -> Double which inlines and simplifies to \ t -> sin t * sin t A more realistic, equivalent, example: let b = sin <$> id in liftA2 (*) b b Can GHC be nudged into computing 'sin t' once rather than twice? Thanks, - Conal

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patch-applied messages
by Christian Maeder 01 Apr '08

01 Apr '08

(resent this request for cvs-ghc(a)haskell.org to glasgow-haskell-users) Hi, could the actual change-diff of patches also be posted via this list (or a web-link to the change)? I think this was the case with the old cvs repository. This would teach a bit Haskell programming and how to write expressive log messages. Currently I never look up changes, although the log messages make me curious sometimes. (I rarely use darcs.) Cheers Christian This is just an example (with an uninteresting diff) > Tue Mar 25 17:49:32 PDT 2008 Ian Lynagh <igloo(a)earth.li> > * Remove a redundant type sig > > M ./compiler/ghci/InteractiveUI.hs -1

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64-bit breakdown
by Jay Scott 31 Mar '08

31 Mar '08

I have a MacBook (which is a Core 2 Duo) running Mac OS X 10.4. On this platform, gcc makes 32-bit executables by default, but if you give it - m64 it makes them 64-bit. I've tried it, and it works. gcc gives its version as "i686-apple-darwin8-gcc-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5367)" But 64-bit doesn't work with my ghc installation (6.8.2 from the binary distribution on the downloads page). If I compile a "Hello World" program with -fvia-c -optc-m64, it fails, saying -- Warning: retaining unknown function `_siC_entry.eh' in output from C compiler Warning: retaining unknown function `_Main_main_entry.eh' in output from C compiler Warning: retaining unknown function `_ZCMain_main_entry.eh' in output from C compiler Prologue junk?: _siC_entry: LFB142: subq $8, %rsp LCFI0: -- I don't need to solve this, but I thought I should make sure it's known. Jay

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Expected behavior of "deriving Ord"?
by Conal Elliott 31 Mar '08

31 Mar '08

I have an algebraic data type (not newtype) that derives Ord: data AddBounds a = MinBound | NoBound a | MaxBound deriving (Eq, Ord, Read, Show) I was hoping to get a min method defined in terms of the min method of the type argument (a). Instead, I think GHC is producing something in terms of compare or (<=). Maybe it's defaulting min altogether. What is the expected behavior in (a) the language standard and (b) GHC? The reason I care is that my type parameter a turns out to have partial information, specifically lower bounds. The type of min allows this partial info to be used in producing partial info about the result, while the type of (<=) and compare do not. Thanks, - Conal

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building against gmp in a nonstandard location
by prj＠po.cwru.edu 30 Mar '08

30 Mar '08

I'm having some trouble building ghc against gmp installed in an unusual place. (Actually, I install every package in its own directory, but gmp seems to be the one causing trouble here.) First attempt: adding the necessary -I, -L, and -Xlinker -R options to CPPFLAGS/LDFLAGS when invoking ./configure, and I also created mk/build.mk to add the -I flags to SRC_CC_OPTS and SRC_HSC2HS_OPTS, and -optc-I, -optl-L, and -optl-Xlinker -optl-R flags to SRC_HC_OPTS. This method worked for ghc 6.6.1, but 6.8.2 gives me: /command/ghc -H16m -O -O2 -optc-I/nil -optc-I/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/gmp/include -optc-I/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/ncurses/include -optc-I/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/readline/include -optc-I/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/binutils/include -optc-pipe -optl-pipe -optc-Os -optl-Os '-optc-march=pentium3' '-optl-march=pentium3' '-optc-mfpmath=sse' '-optl-mfpmath=sse' -optc-msse -optl-msse -optc-mmmx -optl-mmmx -optl-L/nil -optl-L/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/gmp/library -optl-L/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/ncurses/library -optl-L/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/readline/library -optl-L/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/binutils/library -optl-Xlinker -optl-R -optl-Xlinker -optl/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/gmp/library -optl-Xlinker -optl-R -optl-Xlinker -optl/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/ncurses/library -optl-Xlinker -optl-R -optl-Xlinker -optl/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/readline/library -optl-Xlinker -optl-R -optl-Xlinker -optl/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/binutils/library -istage1/utils -istage1/basicTypes -istage1/types -istage1/hsSyn -istage1/prelude -istage1/rename -istage1/typecheck -istage1/deSugar -istage1/coreSyn -istage1/vectorise -istage1/specialise -istage1/simplCore -istage1/stranal -istage1/stgSyn -istage1/simplStg -istage1/codeGen -istage1/main -istage1/profiling -istage1/parser -istage1/cprAnalysis -istage1/ndpFlatten -istage1/iface -istage1/cmm -istage1/nativeGen -Wall -fno-warn-name-shadowing -fno-warn-orphans -Istage1 -cpp -fglasgow-exts -fno-generics -Rghc-timing -I. -Iparser -package unix -ignore-package lang -recomp -Rghc-timing -H16M '-#include "cutils.h"' -DUSING_COMPAT -i../compat -ignore-package Cabal -package directory -package pretty -package containers -c stranal/StrictAnal.lhs -o stage1/stranal/StrictAnal.o -ohi stage1/stranal/StrictAnal.hi <<ghc: 34287668 bytes, 7 GCs, 122880/180224 avg/max bytes residency (2 samples), 19M in use, 0.02 INIT (0.00 elapsed), 0.20 MUT (0.33 elapsed), 0.10 GC (0.10 elapsed) :ghc>> make[1]: *** No rule to make target `stage1//package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/conf/gmp/include/gmp.h', needed by `stage1/parser/cutils.o'. Stop. Second attempt: CPPFLAGS, LDFLAGS and mk/build.mk as above, and I also gave --with-gmp-{includes,libraries} to ./configure. This ends with the same error. Third attempt: all of the above, plus I modified mkdependC.prl to omit dependencies on absolute paths. (I suspect this is wrong, since I assume other people have successfully used gmp in a nonstandard path without having to patch anything, but anyway...) New failure: ../../compiler/stage1/ghc-inplace -Iinclude -package rts-1.0 -optc-O2 -odir dist/build -c cbits/longlong.c -o dist/build/cbits/longlong.o In file included from /fs/pkgs/mount/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/compile/src/ghc-6.8.2/includes/Stg.h:150, from /fs/pkgs/mount/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/compile/src/ghc-6.8.2/includes/Rts.h:19, from cbits/longlong.c:29:0: /fs/pkgs/mount/package/host/code.dogmap.org/foreign/ghc-6.8.2+spf+0/compile/src/ghc-6.8.2/includes/Regs.h:28:17: error: gmp.h: No such file or directory I would have thought the SRC_HC_OPTS options I put in mk/build.mk would be used for this compilation, but apparently not. Does anyone see where the problem might be? paul

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RE: flexible contexts and context reduction
by Sittampalam, Ganesh 27 Mar '08

27 Mar '08

Because I want to be able to make Foo values where the parameter type isn't in Ord, too. I just want unFoo to work on specific Foo values where it is. -----Original Message----- From: Claus Reinke [mailto:claus.reinke@talk21.com] Sent: 27 March 2008 12:25 To: Sittampalam, Ganesh; Ganesh Sittampalam Cc: glasgow-haskell-users(a)haskell.org Subject: Re: flexible contexts and context reduction perhaps i'm missing something but, instead of trying to deduce conditions from conclusions, why can't you just follow ghc's suggestion, and add the constraints to the constructor? data Foo a where Foo1 :: a -> Foo a Foo2 :: (Ord a,Ord b) => Foo a -> Foo b -> Foo (a, b) (possibly with another constraint on Foo1) claus > A closer example to what I was actually doing was this: > > {-# LANGUAGE GADTs #-} > module Foo where > > data Foo a where > Foo1 :: a -> Foo a > Foo2 :: Foo a -> Foo b -> Foo (a, b) > > unFoo :: Ord a => Foo a -> a > unFoo (Foo1 a) = a > unFoo (Foo2 x y) = (unFoo x, unFoo y) > > [in the real code I did actually use the Ord constraint in the base > case] > > The error I get is this: > > Foo.hs:10:20: > Could not deduce (Ord a2) from the context () > arising from a use of `unFoo' at Foo.hs:10:20-26 > Possible fix: add (Ord a2) to the context of the constructor `Foo2' > In the expression: unFoo x > In the expression: (unFoo x, unFoo y) > In the definition of `unFoo': unFoo (Foo2 x y) = (unFoo x, unFoo y) > > Foo.hs:10:29: > Could not deduce (Ord b1) from the context () > arising from a use of `unFoo' at Foo.hs:10:29-35 > Possible fix: add (Ord b1) to the context of the constructor `Foo2' > In the expression: unFoo y > In the expression: (unFoo x, unFoo y) > In the definition of `unFoo': unFoo (Foo2 x y) = (unFoo x, unFoo y) > > Which suggests that GHC has also lost track of the fact that Ord (a, > b) is true. But it would certainly be necessary to get from Ord (a, b) > to (Ord a, Ord b) to get that to work. ============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ==============================================================================

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