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

Hello café! This mail is literate haskell I have some difficulties with understanding how bang patterns and seq works.

{-# LANGUAGE BangPatterns #-} import Control.Monad import Control.Monad.Trans.State.Strict

leak :: State Int () leak = do a <- get put (a+1) leak

This function have obvious space leak. It builds huge chain of thunks so callling `runState leak 0' in ghci will eat all memory. Fix is trivial - add bang pattern. However I couldn't achieve same effect with seq. How could it be done?

noLeak :: State Int () noLeak = do a <- get let !a' = (a + 1) put a' noLeak

Thanks.