Is it not:

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

??

2011/6/9 Alexey Khudyakov <alexey.skladnoy@gmail.com>
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.

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