Re: Arrays and arrays

All right, but why? It seems an obvious trick, take some pieces that benefit from imperative processing, and wrap them in ST, leaving the rest of the program as it were.

Because the reason for your terrible performance is that arrays are being copied willy nilly :). In order to avoid this and to get in-place update (which is what you wanted originally, iirc), you need to do all your modifications inside the ST or IO monad.

Can you (or anybody else) explain the memory behaviour I see (using hundreds of megabytes, but only tens of K visible in the profiling output)?

I cannot :). If your program is short and I can take a look at it, I might be able to say something though.... - Hal