[Haskell-cafe] Euler 201 performance mystery

[nadine.and.henry at pobox.com]

Dear Group,

I've spend the last few days figuring out the solution to Euler Problem 201 in
haskell.  I first tried a relatively elegant approach based on Data.Map but
the performance was horrible.  I never actually arrived at the answer.  I then
rewrote the same algorithm using STUArrays and it was lightning.  I have
posted both versions of the code at:
http://www.maztravel.com/haskell/euler_problem_201.html
and would appreciate any insights that you master haskellers can provide on
why the speed difference is so huge.  Thanks in advance.
Henry Laxen