Re: [Haskell-cafe] Plug space leak with seq. How?

forever a = a>> forever a

doesn't tie to itself without optimisations, so my guess is that it gets expanded when you run/eval/execState it in ghci, building the thunk

a>> a>> a>> a>> ...

If you define

forever' a = let a' = a>> a' in a'

the variant using forever' runs in constant space in ghci. This, like the explicit recursion, builds a cyclic structure, hence avoids the leak.

I see. It's difficult to reason about space complexity in presence of optimizer.