Lazy computation being repeated?

[Jules Bean]

Tyson Whitehead wrote:
> I have a program that seems to me to be exhibiting strange behaviour.  
> Basically, it looks like something somewhere is not being updated, and this is 
> resulting in (very expensive) computation being repeated.

Just a hunch - try recompiling your modules with -fno-state-hack.

q.v. http://hackage.haskell.org/trac/ghc/ticket/2284