May 2003 - Haskell - Haskell.org

Re: problems invoking haddock
by Andre W B Furtado 03 May '03

03 May '03

> This sounds just like what I got with cygwin and Python. You have to > rebase your dll's due to some upgrade/restructure they did, just search > for rebase and cygwin and I'm sure you'll find some text on how to fix > it. Problems, problems, problems... The info I found told me that I should: 1) Download a file called rebase.cc and build it with "g++ -O2 -o rebase rebase.cc -limagehlp" 2) Use the rebase program against some Cygwin DLLs Now here come the problems: a) Trying to build rebase.cc gives me an error: rebase.cc:45: `main' must return `int'. Making main to return 'int' builds the program, but when trying to rebase the DLLs other problem arises: ReBaseImage() failed with last error = 2 b) I found a pre-installed rebase command in cygwin and gave up building rebase.cc. Trying to run this rebase command gives me the error: REBASE: -R must preceed -o. Adding the -R option to the command line, another error arises: REBASE: Total Size of mapping 0x00200000 REBASE: Range 0x67e00000 -0x68000000 Argh! I wonder if haddock has a install shield wizard for Windows! :) Cheers, -- Andre

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unsafe parsing
by Kenny Lu Zhuo Ming 03 May '03

03 May '03

Hi all, I am currently write a program to type a dynamic string consist of 'A' or 'B' for short, it works in this manner: for 'A', it returns A :: A for 'B', it returns B :: B for "A", it returns Cons A Nil :: Cons A Nil for "AB", it returns Cons A (Cons B Nil) :: Cons A (Cons B Nil) ... The problem is I have to specifically annotate the output type, which is unaffordable, because I might have arbitrary-long string, and I have infinitely many possible singleton types. It seems it is impossible to do it in a type-safe way. Anyone of you have any idea to walk around that? Regards, Kenny module Test where data Content = C1 Char | C2 String deriving Eq class MyType a where parse :: Content -> (Maybe a) data A = A deriving (Show,Eq) instance MyType A where parse (C1 'A') = Just A parse _ = Nothing data B = B deriving (Show,Eq) instance MyType B where parse (C1 'B') = Just B parse _ = Nothing data Cons x xs = Cons x xs deriving Show instance (MyType x,MyType xs) => MyType (Cons x xs) where parse (C2 (x:xs)) = let maybehd = parse (C1 x) in case maybehd of Just hd -> let maybetl = parse (C2 xs) in case maybetl of Just tl -> Just ((Cons hd) tl) Nothing -> Nothing Nothing -> Nothing parse _ = Nothing data Nil = Nil deriving (Show,Eq) instance MyType Nil where parse (C2 []) = Just Nil parse _ = Nothing %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% Hugs session for: /usr/share/hugs/lib/Prelude.hs Test.hs Type :? for help Test> parse (C2 "A") :: Maybe (Cons A Nil) Just (Cons A Nil)

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RE: problems invoking haddock
by Marcus Lindblom 02 May '03

02 May '03

From: "Andre W B Furtado" <andrefurtado(a)ieg.com.br> Is the following problem a specific cygwin problem and how can I overcome it? It happened to me while trying to invoke haddock: > /cygdrive/c/haskell/cygwin/usr/local/bin/haddock: > Cannot fork: Resource temporarily unavailable This sounds just like what I got with cygwin and Python. You have to rebase your dll's due to some upgrade/restructure they did, just search for rebase and cygwin and I'm sure you'll find some text on how to fix it. /Marcus

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a nice Pair,, was: Multiparameter classes in HUGS and GHC
by Lloyd Allison 02 May '03

02 May '03

On Wed, Apr 30, 2003 at 07:20:06PM +0100, Graham Klyne wrote: > I've trying to understand better how to use multiparameter classes, and in > particular the things that can be declared as instances. I've consulted > the following: > ... > [[ > class (Eq k, Show k) => Pair a k v where > newPair :: (k,v) -> a k v > getPair :: a k v -> (k,v) > > newtype MyPair1 k v = P1 (Int,String) > > instance Pair MyPair1 Int String where > newPair (x,y) = P1 (x,y) > getPair (P1 (x,y)) = (x,y) > ... --The nicest Pair that I've ever managed is not: class Pair p a b where -- if we use fst' then b is "loose" and v.v. fst' :: p->a -- seems to be :: forall a.(p->a), regardless class Pair p. snd' :: p->b -- can't seem to get a and b from the instances. -- Seems to be a problem overloading both fst and snd in one class -- but OK if one operator per class ... --But rather: -- ... so we can split Pair into two classes, "left" and "right"! class PairL p a where fst'' :: p->a -- OK but a needs to be implied by use class PairR p b where snd'' :: p->b -- ditto instance PairL (((,) a b)) a where fst'' (x,y) = x instance PairR (((,) a b)) b where snd'' (x,y) = y -- could make (a trivial) Pair' a subclass of PairL and PairR --which incidentally will combine with class Function fnType t u where ($) :: fnType -> t -> u -- NB hid std $ instance Function (t->u) t u where f $ x = f x -- Hask' list 29 Oct 2002 --allowing instance Function ((t->u),(v->w)) (t,v) (u,w) where (f, g) $ (x, y) = (f x, g y) --e.g. f2b = ( (\ch->if ch=='a' then 'z' else ch), (not) ) ... ( (f2b $ ('a', False)) :: (Char,Bool) ) -- need the type ... Lloyd -- Lloyd ALLISON, CSSE, Monash University, Victoria, Australia 3800. web: http://www.csse.monash.edu.au/~lloyd/ tel: +61 3 9905 5205 use: http://www.linux.org/ OpenOffice: http://www.openoffice.org/

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Typing problems with polymorphic recursion and typeclasses
by oleg＠pobox.com 01 May '03

01 May '03

[Commenting of the problem in the message "GHC doesn't like its own type?", Iavor Diatchki wrote] > i remeber some time ago levent erkok run intro a simillar problem. take > a look at this post: > http://www.mail-archive.com/haskell@haskell.org/msg06754.html The problems seem different. However, Levent Erkok's problem as well as the problem in the follow-up message to categorical maxima point out that there is something else goes on besides the explicit typing. Let us use Levent Erkok's problem as it is simpler: > class X a where > u :: a b -> a b > f :: X a => b -> a b > f = f > g :: X a => a b -> b > g = g > -- h :: X a => b -> a c > h b = f (g (h b)) This file loads and checks both in GHC and Hugs. The problem is that if we uncomment the explicit type declaration of h (which is identical to the inferred type reported by the compiler), typechecker complains. Let us keep the function h without the explicit type declaration. Let us apply what I thought as an equivalent transformation: > h = \b -> f (g (h b)) Hugs now reports ERROR "/tmp/b.hs":12 - Unresolved top-level overloading *** Binding : h *** Outstanding context : X b and GHCi reports /tmp/b.hs:12: Ambiguous type variable(s) `a' in the constraint `X a' arising from use of `f' at /tmp/b.hs:12 In a lambda abstraction: f (g (h b)) It is interesting that the error message is exactly the same as when we used the explicit type declaration for the old "h b=..." definition. Something seems to be going on...

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problems invoking haddock
by Andre W B Furtado 01 May '03

01 May '03

Is the following problem a specific cygwin problem and how can I overcome it? It happened to me while trying to invoke haddock: > $ haddock -h hello.hs > C:\haskell\cygwin\bin\sh.exe: *** fork: can't reserve memory for stack > 0x40000 - > 0x240000, Win32 error 487 > 4 [main] sh 1212 sync_with_child: child 988(0x72C) died before > initialization with status code 0x1 > 8217 [main] sh 1212 sync_with_child: *** child state > waiting for longjmp > C:\haskell\cygwin\bin\sh.exe: *** fork: can't reserve memory for stack > 0x40000 - 0x240000, Win32 error 487 > 19746 [main] sh 1212 sync_with_child: child 11816(0x720) died before > initialization with status code 0x1 > 19941 [main] sh 1212 sync_with_child: *** child state > waiting for longjmp > /cygdrive/c/haskell/cygwin/usr/local/bin/haddock: Cannot > fork: Resource > temporarily unavailable Cheers, -- Andre

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GHC doesn't like its own type?
by oleg＠pobox.com 01 May '03

01 May '03

The previously message "Deeply uncurried products, as categorists might like them" can be used to demonstrate certain behavior of GHC that seems a bit odd. If we save the text of that message in a file, /tmp/a.lhs, we can load it into GHC: $ ghci -fglasgow-exts /tmp/a.lhs GHC Interactive, version 5.04.1 Ok, modules loaded: Main. *Main> The whole code loads and typechecks. The code contains the following definition, without an explicit type signature: > fcomp a = (. fapp) (mcomp a) We can ask GHCi to tell us the type of fcomp: *Main> :type fcomp forall result f1 a f2 c cp. (FApp a cp c, MCompose f2 cp c result) => (f1 -> f2) -> a -> f1 -> result and make that type, verbatim, to be the signature of fcomp: > fcomp:: forall result f1 a f2 c cp. (FApp a cp c, MCompose f2 cp c result) => (f1 -> f2) -> a -> f1 -> result > fcomp a = (. fapp) (mcomp a) If we reload the file, we get an error: /tmp/a.lhs:124: Could not deduce (FApp a cp c1) from the context (FApp a cp c, MCompose f2 cp c result) Probable fix: Add (FApp a cp c1) to the type signature(s) for `fcomp' arising from use of `fapp' at /tmp/a.lhs:124 In the second argument of `(.)', namely `fapp' In the definition of `fcomp': (. fapp) (mcomp a) /tmp/a.lhs:124: Could not deduce (MCompose f2 cp c1 result) from the context (FApp a cp c, MCompose f2 cp c result) Probable fix: Add (MCompose f2 cp c1 result) to the type signature(s) for `fcomp' arising from use of `mcomp' at /tmp/a.lhs:124 In the first argument of `(. fapp)', namely `(mcomp a)' In the definition of `fcomp': (. fapp) (mcomp a) I used to think that the inferred type is the most general type, and that the compiler would accept as explicit the type that it itself inferred. I was wrong? The second odd circumstance is best illustrated by the following transcript. Assume that /tmp/a.lhs is the text of the previous message as it was posted: $ ghci -fglasgow-exts /tmp/a.lhs GHC Interactive, version 5.04.1, for Haskell 98. Loading package base ... linking ... done. Loading package haskell98 ... linking ... done. Compiling Main ( /tmp/a.lhs, interpreted ) /tmp/a.lhs:76: Warning: No 'main' defined in module Main Ok, modules loaded: Main. *Main> let x = \f -> fapp f (('a','b'),('c',('d','e'))) Bus error (core dumped) Incidentally, if I enter > x = \f -> fapp f (('a','b'),('c',('d','e'))) into /tmp/a.lhs and load the file into GHCi, I get ghc-5.04.1: panic! (the `impossible' happened, GHC version 5.04.1): rdrNameModule zddFApp

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