Bizarre Haskell Problem

[Daan Leijen]

My guess is that you are having an out-of-date .o of .hi file
in your working directory. Clean it up and try again.

All the best,
    Daan.

----- Original Message -----
From: "Matthew Donadio" <m.p.donadio@ieee.org>
To: <haskell@haskell.org>
Sent: Monday, January 27, 2003 10:34 PM
Subject: Bizarre Haskell Problem


> Hi all,
>
> I am currently a having a bizarre Haskell problem, and was wondering if
> anyone had any suggestions.
>
> This is a snippet from a source file:
>
> > foo n = [ a ^* i | i <- [0..(n-2)] ]
> >     where i ^* j = (i ^ j) `mod` n
> >     a = generator n
>
> > rader :: Array Int (Complex Double) -> Int -> Array Int (Complex Double)
> > rader f n = foo a n -- DEBUG: should be f'
> >     where h = listArray (0,n-2) [ f!(a ^* (n-(1+n'))) | n' <- [0..(n-2)] ]
> >           g = listArray (0,n-2) [ w (a ^* n') | n' <- [0..(n-2)] ]
> >           f' = array (0,n-1) ((0, sum [ f!i | i <- [0..(n-1)] ]) : [ (a ^* i, f!0 + sum [ h!j *
g!((i-j)`mod`(n-1)) | j <- [0..(n-2)] ]) | i <- [0..(n-2)] ])
> >           w i = cis (-2 * pi * fromIntegral i / fromIntegral n)
> >           i ^* j = (i ^ j) `mod` n
> >     a = generator n
>
> Under hugs and ghc, calling 'foo' and 'rader' with the proper arguments
> will give me different results under certain circumtances.
>
> In rader, n is the number of elements in the array.  If n is < 23, then
> everything is OK.  If n >= 23, then rader returns the wrong result.  The
> bizarre thing is that if I comment out the definitions of h and f' in
> rader, then it returns the correct results.  Hugs also give different
> reduction counts depending on whether h and f' are commented out or
> not.  If I add any more definitions that reference f, then rader
> misbehaves.
>
> What is even more bizarre is that if I copy everything into a separate
> file, then it work for all n.
>
> Any suggestions or hints, other than just use a separate file?  Separate
> files isn't really an option, because the above is simplified a bit, and
> the final version would have mutually recursive modules, which hugs
> can't handle.
>
> Thanks.
>
> --
> Matthew Donadio (m.p.donadio@ieee.org)
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