In odd spare moments, I took John Harrops simple ray tracer[1] & made a Haskell version: http://www.kantaka.co.uk/cgi-bin/darcsweb.cgi?r=ray darcs get http://www.kantaka.co.uk/darcs/ray It's pretty much a straight translation into idiomatic Haskell (as far as my Haskell is idiomatic anyway). Unfortunately, it's a lot slower than the ML version, despite turning all the optimisation options up as far as they'll go. Profiling suggests that much of the time is spent in the intersection' function, and that the code is creating (and garbage collecting) an awful lot of (-|) vector subtraction thunks. Trying to make intersection' or ray_sphere stricter (with seq) appears to have no effect whatsoever: the output of -ddump-simpl is unchanged (with the arguments all staying lazy). Am I missing anything obvious? I don't want to carry out herculean code rewriting efforts: that wouldn't really be in the spirit of the thing. cheers, Phil [1] http://www.ffconsultancy.com/languages/ray_tracer/comparison.html -- http://www.kantaka.co.uk/ .oOo. public key: http://www.kantaka.co.uk/gpg.txt