[Haskell-cafe] Hugs faster and more reliable than GHC for large
list monad 'do' block
westondan at imageworks.com
Thu Aug 6 16:59:45 EDT 2009
I assume for the return line, you meant to return a list, not a tuple.
ghc doesn't support a 600-tuple.
In any case, returning a list, I have verified that this problem exists
in ghc 6.10.3, for -O0 and -O2.
For -O0, it compiles and links fine, but gives this runtime message:
z: internal error: scavenge: unimplemented/strange closure type -1 @
(GHC version 6.10.3 for x86_64_unknown_linux)
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
Maybe it is attempting to unroll these loops, even with -O0?
Henning Thielemann wrote:
> Today a student has shown me a program that consists of a large 'do'
> block for the list monad. The program looks like
> do x1 <- [0..3]
> x2 <- [0..2]
> x600 <- [0..5]
> guard (x1+x2+2*x3 >= 0)
> return (x1,x2,....,x600)
> It was actually generated by another program. The results were:
> GHC-6.4 was not able to compile that program at all, because it stopped
> because of memory exhaustion.
> GHC-6.8.2 finished compilation after two minutes but the program aborted
> quickly because of a corrupt thunk identifier.
> GHC-6.10 not yet tested.
> Hugs-2006 executed the program without complaining and showed the first
> result after a few seconds: (0,0,0,0,0,...,0).
> Eventually the program must run on a Linux cluster with a not up-to-date
> Linux kernel, that is, I suspect newer GHC versions cannot be used due to
> the 'timer_create' problem. (At least, the 'cabal' executable that I
> generated with a GHC-6.8.2 had this problem when running on the cluster
> which reminded me on the problems with GHC-6.8 itself running on older
> Linux kernels.)
> Since the list monad sorts the variable values in lexicographic order
> which is inappropriate for the considered problem, I recommended the use
> of control-monad-omega. Luke, I hope this monad can cope with 600
> variables. :-)
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