Hello haskell-cafe, Let me repost here a question I posted to cstheory stackexchange - in hopes that there are more type theory experts here. http://cstheory.stackexchange.com/questions/29518/type-systems-preventing-la... Perhaps the main source of performance problems in Haskell is when a program inadvertently builds up a thunk of unbounded depth - this causes both a memory leak and a potential stack overflow when evaluating. The classic example is defining sum = foldr (+) 0 in Haskell. Are there any type systems which statically enforce lack of such thunks in a program using a lazy language? Seems like this should be on the same order of difficulty as proving other static program properties using type system extensions, e.g. some flavors of thread safety or memory safety.