- Glasgow-haskell-users

RE: RFC: External library infrastructure
by Simon Marlow 13 Nov '02

13 Nov '02

> I was thinking "add all the things that make packages insufficient > to use as an infrastructure" :-) > > One thing is autoconf support for those doing ffi. > We might also want conditionals in package specs (cpp enough?). > > I don't see Makefiles as part of a cross-compiler story. Rather, I > see an enhanced package system that includes a subset of makefile > functionality (e.g., Hugs' import chasing and GHC's --make > functionality). And the enhanced package system is implemented in each compiler? Or just once in the infrastructure, perhaps by a script? Or a mixture of the two? One difficulty is that if the infrastructure requires certain extensions to the package system, then we can't start using it until new compilers come out that have the required extensions. There are some aspects of the infrastructure that I really don't want to provide in GHC as part of its package system: the details of building libraries several ways, installing them in the right place, building and installing documentation, etc. etc. So I think this stuff belongs in the infrastructure one way or another. However, I'm not proposing to implement this stuff (I'm hoping someone else will volunteer ;-) so whoever does the job gets to choose the implementation strategy. Obviously we'll help out with any extensions to GHC that are needed. Cheers, Simon

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RE: Floats and Doubles
by Simon Marlow 13 Nov '02

13 Nov '02

> But this brings up a strange thing in GHCi. Suppose I load > the following module into GHCi: > > \begin{code} > module Foo where > > kalle = (fromRational ((toRational 4) - ( toRational 5.2 ))) > > default (Rational) > \end{code} > > What happens is the following: > > Prelude> :l Foo.hs > Compiling Foo ( Foo.hs, interpreted ) > Ok, modules loaded: Foo. > *Foo> kalle > (-6) % 5 > *Foo> (fromRational ((toRational 4) - ( toRational 5.2 ))) > -1.2000000000000002 > > It seems like GHCi doesn't care about the default directive > on the promt. This is a known bug: http://sourceforge.net/tracker/index.php?func=detail&aid=431362&group_id =8032&atid=108032 Cheers, Simon

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Re: Class/Implicit Param/Module Interface bug
by Ashley Yakeley 13 Nov '02

13 Nov '02

Actually it's worse than that. This crashes: module Main where { import A; main = let {?p="test"} in putStrLn f; -- BUG: this crashes -- main = let {?p="test"} in putStrLn g; -- this works } -- Ashley Yakeley, Seattle WA

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Floats and Doubles
by Juan Ignacio Garcia Garcia 13 Nov '02

13 Nov '02

hello, I have been using some of the functions of the classes Real and Fractional and I have observed that with the funcion "toRational" we can obtain the fraction that represents a given number. For instance: *P2> toRational (5.2::Float) 5452595 % 1048576 Why we obtain this numbers instead of "52 % 10" or "26 % 5"? I have also obtained the following results with the functions "fromRational" and "toRational": *P2> (fromRational ((toRational 4) - ( toRational (5.2::Float) )))::Double -1.1999998092651367 *P2> (fromRational ((toRational 4) - ( toRational (5.2::Double) )))::Double -1.2000000000000002 *P2> (fromRational ((toRational 4) - ( toRational 5.2 ))) -1.2000000000000002 *P2> (fromRational ((toRational 4) - ( toRational (5.2::Float) )))::Float -1.1999998 Are all these results ok? If this is the case, why? Thanks, Ignacio

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Class/Implicit Param/Module Interface bug
by Ashley Yakeley 13 Nov '02

13 Nov '02

My program was crashing and I couldn't figure out why. Then I discovered this strange bug involving classes, implicit parameters, and module interfaces (see enclosed files). Basically the type-checker is not being strict enough and misses this compile-time error. The workaround, of course, is not to make the error. module A where { class C a where { f :: (?p :: String) => a; }; instance C String where { f = ?p; }; g :: (?p :: String) => String; g = ?p; } {-- Compile using this: ghc -fglasgow-exts -c A.hs && ghc -fglasgow-exts A.o Main.hs -o bug && ./bug Bug won't happen with --make: rm bug; rm *.hi *.o; ghc -fglasgow-exts --make Main.hs -o bug && ./bug Bug won't happen if everything is in one module. --} module Main where { import A; main = putStrLn f; -- BUG: this compiles (and crashed when run, of course) -- main = putStrLn g; -- this correctly gives a compile-time error } $ ghc --version The Glorious Glasgow Haskell Compilation System, version 5.04 $ uname -a Darwin Ashley-Yakeleys-Computer.local. 6.2 Darwin Kernel Version 6.2: Tue Nov 5 22:00:03 PST 2002; root:xnu/xnu-344.12.2.obj~1/RELEASE_PPC Power Macintosh powerpc -- Ashley Yakeley, Seattle WA

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RFC: External library infrastructure
by Simon Marlow 13 Nov '02

13 Nov '02

Hi Folks, It has occurred to us that the GHC community really needs an infrastructure (i.e. like a build system, but more) that people can use for shipping their own libraries independently of GHC. Several people have asked recently if they can ship their libraries with GHC - for a while we were quite receptive to this, but GHC is getting rather "heavy" both in terms of build time and maintenance effort, and we feel it's time to cut back a bit. But we don't want to leave library developers out in the cold. Suppose we had an infrastructure which someone could plug their library source code into, and immediately get - a source tarball which will configure/build/install on a Unix/cygwin system with GHC installed, and provide a GHC package when installed. - skeleton binary packages for RPM, Windows installer, *BSD ports, Gentoo ebuild, etc. The binary packages will require some programmer intervention (such as setting the dependencies correctly), but much of the work can be done automatically. Furthermore, we'd provide links to compatible library packages from the GHC web pages. It doesn't particularly matter whether fptools is used as a starting point, or we pick another existing build system or start from scratch. The important thing is that someone who wants to ship a library can pick up this infrastructure and quickly provide all the above functionality with very little extra work. Comments? Cheers, Simon

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RE: Floats and Doubles
by Simon Marlow 12 Nov '02

12 Nov '02

> I have been using some of the functions of the classes Real and > Fractional and I have observed that with the funcion > "toRational" we can > obtain the fraction that represents a given number. For instance: > *P2> toRational (5.2::Float) > 5452595 % 1048576 > Why we obtain this numbers instead of "52 % 10" or "26 % 5"? Because you asked for the number to be converted to a Float first, and 5.2 can't be represented exactly in a single-precision float. If you don't go via Float, you get the exact result: Prelude> 5.2 :: Rational 26 % 5 > I have also obtained the following results with the functions > "fromRational" and "toRational": > *P2> (fromRational ((toRational 4) - ( toRational > (5.2::Float) )))::Double > -1.1999998092651367 > *P2> (fromRational ((toRational 4) - ( toRational > (5.2::Double) )))::Double > -1.2000000000000002 > *P2> (fromRational ((toRational 4) - ( toRational 5.2 ))) > -1.2000000000000002 > *P2> (fromRational ((toRational 4) - ( toRational > (5.2::Float) )))::Float > -1.1999998 These are all symptoms of rounding. Cheers, Simon

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Re: Generating a Windows executable
by Chris Saunders 12 Nov '02

12 Nov '02

I discovered what my problem was. I was not aware that the executable would be deposited into the current working directory of the command prompt. Since the intermediate files were generated in the same folder as the source file, I assumed the .exe would go there also. The executable was generated correctly with the command lines suggested by both Seth and Hal - and thanks for your responses. Regards Chris Saunders chris.saunders.@sympatico.ca

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Building a Windows executable
by Chris Saunders 12 Nov '02

12 Nov '02

I am new to Haskell and GHC and am using a tutorial that I found on the Web to learn. In the tutorial it says that a command like this can be used to build an executable (Windows): ghc --make test.hs -o test.exe The compiler had no complaints and output 2 files: Main.hi and test.o This is the code I was attempting to compile: module Main where main = putStrLn "Hello World." I also tried using: ghc --make test.hs and got the same result. Sorry for such a lame question. Regards Chris Saunders chris.saunders.@sympatico.ca

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functional dependency syntax?
by Malcolm Wallace 11 Nov '02

11 Nov '02

I'm trying out MPTC with functional dependencies for the first time in GHC. However, I'm not sure of the syntax. MPJ's ESOP 2000 paper gives the following example: class FiniteMap i e fm | fm -> (i,e) where emptyFM :: fm lookupFM :: i -> fm -> Maybe e extendFM :: i -> e -> fm -> fm but ghc (5.02.2 and 5.04.1) complain $ ghc-5.04.1 -fglasgow-exts -c -o FunDep.o FunDep.hs FunDep.hs:10: parse error on input `(' where the indicated line is that of the class declaration. What should the syntax be if it is not the above? Regards, Malcolm

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