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

[Alexey Khudyakov]

On 09.06.2011 20:09, Yves Parès wrote:
> Is it not:
>
>  > noLeak :: State Int ()
>  > noLeak = do
>  >   a <- get
> *>* *let a' = (a + 1)
>  >   a' `seq` put a'*
>  >   noLeak
>
> ??
>

Indeed. Now I understand. It didn't work for me earlier because of
different behavior of 'forever' in ghci and compiled code.

This function leaks in ghci and do not in compiled code without 
optimizations (with optimizations GHC is smart enough  to make 
everything strict).

 > noLeak = forever $ do { a <- get; let a' = a+1; a' `seq` put a' }

Function with explicit recursion do not leak in both cases.

 > noLeak = do { a <- get; let a' = a+1; a' `seq` put a'; noLeak }

What causes this difference?