[Haskell-cafe] Monad explanation

[Tony Morris]

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You're right - my statement is inaccurate.

Implementation details aside, I am referring specifically to the
statement "getChar ... has the type signature of a value". It clearly
does not.

Lennart Augustsson wrote:
> Not it doesn't.  getChar has the type signature IO Char. The IO
> type is abstract.  GHC happens to implement it by a state monad.
> But in, e.g., hbc it is implemented in a totally different way,
> more like a continuation monad.
>
> Peeking inside an implementation of IO can be illuminating, but one
> must remember that IO is abstract.
>
> -- Lennart
>
> On Mon, Feb 9, 2009 at 10:26 AM, Tony Morris <tmorris at tmorris.net>
> wrote: Gregg Reynolds wrote:
>>>> The point being that the metalanguage commonly used to
>>>> describe IO in Haskell contains a logical contradiction.  A
>>>> thing cannot be both a value and a function, but e,g, getChar
>>>> behaves like a function and has the type signature of a
>>>> value.
> getChar has the signature RealWorld -> (RealWorld, Char)
>
>>
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- --
Tony Morris
http://tmorris.net/

S, K and I ought to be enough for anybody.

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