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List:       haskell-cafe
Subject:    Re: [Haskell-cafe] Plug space leak with seq. How?
From:       Alexey Khudyakov <alexey.skladnoy () gmail ! com>
Date:       2011-06-10 9:11:24
Message-ID: 4DF1DFBC.8060701 () gmail ! com
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>
> 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.

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