[Haskell-cafe] Re: evaluation semantics of bind
gleb.alexeev at gmail.com
Thu Feb 5 11:49:02 EST 2009
Gregg Reynolds wrote:
> I must be misunderstanding something. I don't know if it would be
> optimized out, but I see no reason why it couldn't be. There's no data
> dependency, right?
Of course there is data dependency. In my example, where IO is defined
as a (generalized) algebraic datatype, the value of getChar is GetChar.
The value of 'getChar >>= \x -> getChar' is 'Bind GetChar (\x ->
GetChar'. 'x' is not used anywhere, but this doesn't change the fact
that these are totally different values, no sane compiler would prove
For some monads, the evaluation of 'a >>= \x -> b' yields b, but it's
not true in general.
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