- Glasgow-haskell-users

Problem with ghc-5-04-1.msi
by David Sabel 23 Oct '02

23 Oct '02

While installing the file the following error occurs: Invalid Drive c:\ after that error message the "GHC setup ended prematurely because of an error" My Computer doesn't have a drive c:\, the windows partition is on d:\. The previous .msi-Version (5.04) didn't have this error. David

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Publications from Chipworks
by Chipworks＠haskell.org 23 Oct '02

23 Oct '02

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RE: deriving weirdness on newtypes
by Simon Peyton-Jones 22 Oct '02

22 Oct '02

Hal I have fixed this bug in the HEAD. The fix is more than a tiny one, so I'm inclined to leave it as a know bug in 5.02.2. It'd cost me another few hours to patch it into the 5.02 branch. I don't think this is a widely-used feature, yet. Even John Hughes didn't notice the bug. Simon | -----Original Message----- | From: Hal Daume III [mailto:hdaume@ISI.EDU] | Sent: 02 October 2002 18:58 | To: GHC Users Mailing List | Subject: deriving weirdness on newtypes | | So I love the fact that I can derive anything I want on | newtypes. However, there seem to be problems with it. If I write: | | newtype Foo = Foo Int deriving (Show) | x = show (Foo 5) | | Then x is "Foo 5" | | However, if I do | | newtype Foo = Foo Int deriving (Num) | x = show (Foo 5) | | Then the definition of 'x' claims that there is no Show instance of Foo. | | However (this is where it gets weird). If I do: | | newtype Foo = Foo Int deriving (Num) | x = show ((Foo 5) + 4) | | then x is *valid* and has value "9", not "Foo 9". Moreoever, I can even | do: | | x = show ((5::Foo) + 4) | | and this x has value "9". | | Futhermore, if I do: | | newtype Foo = Foo Int deriving (Show,Num) | | then "show (Foo 5)" has value "5", not "Foo 5". | | IMO, the correct value of "show (Foo 5)" no matter which of the above we | have is "Foo 5". I think the deriving mechanism should be changed in two | ways. | | (1) If you derive X on a newtype and X is a subclass of Y, | you must have an instance of Y on that newtype. This is | how it works on data types, and I think makes sense. | For instance, | newtype Foo = Foo Int deriving (Ord) | should be just as illegal as | data Foo = Foo Int deriving (Ord) | | (2) The derived Show instances for newtypes in the presense of | derived Num instances should be fixed so that the | constructor is also printed. Rational: adding something | to the list of derived classes should *not* change | previously derived instances. | | There is yet another thing. If we have: | | newtype Foo = Foo Int deriving (Num) | instance Show Foo where { show = undefined } | | then, the value of 'show (Foo 5)' is undefined, but the value of 'show | (5::Foo)' is "5". definately *WRONG*. | | - Hal | | -- | Hal Daume III | | "Computer science is no more about computers | hdaume(a)isi.edu | than astronomy is about telescopes." -Dijkstra | www.isi.edu/~hdaume | | _______________________________________________ | Glasgow-haskell-users mailing list | Glasgow-haskell-users(a)haskell.org | http://www.haskell.org/mailman/listinfo/glasgow-haskell-users

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RE: more undecidable instances, but why
by Simon Peyton-Jones 22 Oct '02

22 Oct '02

| instance MArray IOUArray a IO => MArray IOUArray (S a) IO where | However, GHC complains: | | /nfs/isd/hdaume/projects/MESumm/Linear2/Linear2.hs:76: | Non-type variables in constraint: MArray IOUArray a IO | (Use -fallow-undecidable-instances to permit this) | But I don't see why this is undecidable. As I understand it, undecidable | instances basically arise when context reduction might not | terminate. Here, it always will (AFAICS). In this case it's not undecideable, but GHC isn't clever enough to spot that. The point is that that each of the types on the left of the => are smaller than the types on the right MArray IOUArray a IO Is smaller than MArray IOUArray (S a) IO But GHC isn't clever enough to spot that. In general it's the halting problem. Doubtless there are useful special cases. Simon

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Sesso ma vero...
by Giada 22 Oct '02

22 Oct '02

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FFI : A failing example
by Francis Girard 22 Oct '02

22 Oct '02

Hello, I'm a beginner trying to use FFI. I copied the example given in : The Glasgow Haskell Compiler User's Guide, Version 5.04 Chapter 8. Foreign function interface (FFI) -------------------------------------------------------------------------- module Foo where foreign export ccall foo :: Int -> IO Int foo :: Int -> IO Int foo n = return (length (f n)) f :: Int -> [Int] f 0 = [] f n = n:(f (n-1)) -------------------------------------------------------------------------- Copied it verbatim. And simply tried to compile it using "ghc -c Foo.hs -o Foo.o" and always got the error : Type signature given for an expression (at the line following the "foreign export") I then tried to import the "Foreign" and "Foreign.C" modules but it didn't change anything. I am missing something and I would be VERY grateful to anyone that tells me what. Thank you Francis Girard Le Conquet (France) Francis.Girard(a)free.fr

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RE: Optimisation
by Simon Marlow 21 Oct '02

21 Oct '02

> What's the standard paper about optimisations and program > transformation? A recent one is "Secrets of the GHC inliner", available here: http://www.research.microsoft.com/~simonpj/Papers/inlining/index.htm The other good place to look is Andre Santos's thesis (sorry, I don't have a URL for that handy). > Which transformations are used by the GHC, especially which > optimisations are applied at optimisation level 0, 1 and 2? The only transformation which is currently applied at level 2 but not level 1 is constructor specialisation (it is experimental and we haven't measured the benefit yet). Level 1 has everything else turned on, and level 0 has simplification only. Cheers, Simon

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Optimisation
by David Sabel 21 Oct '02

21 Oct '02

What's the standard paper about optimisations and program transformation? Which transformations are used by the GHC, especially which optimisations are applied at optimisation level 0, 1 and 2? David Sabel JWGU Frankfurt

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RE: compiler/doc discrepancy
by Simon Marlow 21 Oct '02

21 Oct '02

> For the profiling -i option, the compiler tells me the value is > microsecond (default 100), while the GHC documentation claims seconds > (default 0.1). > > Apparently, the documentation is correct? Yes, I noticed this one recently, it's been fixed in the tree. Cheers, Simon

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compiler/doc discrepancy
by ketil＠ii.uib.no 21 Oct '02

21 Oct '02

For the profiling -i option, the compiler tells me the value is microsecond (default 100), while the GHC documentation claims seconds (default 0.1). Apparently, the documentation is correct? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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