2009/2/9 Gregg Reynolds
Right; "implementation of IO" means also an implementation for >>=, not just the IO operators. I hadn't thought about that but it's hugely important for the exposition of monads and IO.
"The IO Char indicates that getChar, when invoked, performs some action which returns a character." (Gentle Intro, typical of many expositions.)
In this case, I think "invoked" is shorthand for "interpreted by the runtime system".
That, plus the form of \x -> putChar x used with >>=, plus the fact that one can do getChar at the ghci command line, plus all the other stuff - it all adds up to exasperation.
It's worth noting that ghci, unlike Haskell itself, *does* treat IO
specially. It checks the type of the expression you've entered, and
behaves differently depending on whether it's equal to a, IO a, or IO
().
interp[ e :: IO () ] = e
interp[ e :: IO a ] = e >>= print
interp[ e :: a ] = print e
This is convenient for users, but it has nothing to do with the
semantics of Haskell.
--
Dave Menendez