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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