Proposal: Add modify' to Control.Monad.State.Strict

Code like flip execState 0 (forever $ modify (+1)) leaks memory as hell, and gets fixed by using x <- get put $! x + 1 I propose the addition of modify' to Control.Monad.State.Strict. This seems useful for the strict state monad and is consistent with similar functions in base (such as modifyIORef'). Discussion period: 2 weeks.