November 2002 - Glasgow-haskell-users

Help: Windows ghc profiler errors
by Bayley, Alistair 14 Nov '02

14 Nov '02

I want to profile my Haskell program (it solves the Queens and Knights problem stated here: http://www.itasoftware.com/careers/programmers.php ). I'm compiling with GHC 5.04.1 under Windows NT using the following command line (as per the Users Guide): >ghc -prof -auto-all -o queens --make Main When I run the program with the following command lines I get: >queens queens: fatal error: evacuate: strange closure type 1696 >queens +RTS queens: fatal error: evacuate: strange closure type 1728 >queens +RTS -p queens: fatal error: evacuate: strange closure type 1760 (I have no idea if the change in closure type is significant, but it is quite clearly related to the command line options used.) The program works without profiling (whether or not it produces the correct answers is another matter). I just want to practice profiling and optimising Haskell programs. I've also tried running the profiler with a minimal program: > module Main where > main :: IO () > main = do putStrLn "hello world" ... and I get a segmentation fault. Anyway, I've had a quick look through the last couple of months of mailing list archives and haven't noticed anything related to this error. Any ideas? Thanks, Alistair. ***************************************************************** The information in this email and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal professional or other privilege or may otherwise be protected by work product immunity or other legal rules. It must not be disclosed to any person without our authority. If you are not the intended recipient, or a person responsible for delivering it to the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it. *****************************************************************

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-Werror Request
by Ashley Yakeley 13 Nov '02

13 Nov '02

If it's not too much work, I'd like to request a "-Werror" option for GHC that would turn warnings into errors. Sometimes warnings one would like to catch get lost in a long make process. Thanks... -- Ashley Yakeley, Seattle WA

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strange error
by John Meacham 13 Nov '02

13 Nov '02

fatal error: evacuate: strange closure type 55436 although I have not been able to reproduce it... -- --------------------------------------------------------------------------- John Meacham - California Institute of Technology, Alum. - john(a)foo.net ---------------------------------------------------------------------------

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Re: Record of STRefs better than STRef to a Record?
by Jorge Adriano 13 Nov '02

13 Nov '02

> > I'm passing that 'record' around as an implicit value. The record as > > STRefs that I use to collect info, but it also has some pure fields with > > 'read-only' info. Something like, <opss let me change 'max' to 'm'> > > data E s = E{ > > refi :: STRef s Int, > > refc :: STRef s Char, > > m :: Int > > } > > > > In some functions I might need only some pure fields, and none of the > > STRefs, but since I pass something of type 'E s' around, everything ends > > up beeing monadic. > > there is no reason why that should be the case. you only need to be > within the ST monad when you read the references, so if in some function > you only look at the pure values, it can have a pure type. > hope this helped > iavor That's what I thought, untill I tried it. Well, actually you must be right since the pure field defines a pure (projection) function... Hmmm, ok, can someone explain this to me, data E s = E{ refi :: STRef s Int, refc :: STRef s Char, m :: Int } -- this is fine, obviously... pure :: E s -> Int pure e = m e -- but this is not... pure2 :: (?e :: E s) => Int pure2 = m (?e) Why exactly isn't this allowed? What is the workaround? Error msg: ------------------------------------------------------------------------ Ambiguous constraint `?e :: E s' At least one of the forall'd type variables mentioned by the constraint must be reachable from the type after the '=>' In the type: forall s. (?e :: E s) => Int While checking the type signature for `pure2' Failed, modules loaded: none. -------------------------------------------------------------------------- Thanks, J.A.

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Record of STRefs better than STRef to a Record?
by Jorge Adriano 13 Nov '02

13 Nov '02

Hi all, If I use an STRef to a record, will a new record be created each time I want to update a single field? Or can I expect GHC to optimize it and have the field of the record updated in place? Right now I'm using a record of STRefs, like: data E s = E{ refi :: STRef s Int, refc :: STRef s Char } but it can get a little messy, since thread s propagates to every datatype that uses the record type in it's definition. Thanks, J.A.

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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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