Fwd: Re: Yet Another Monad Tutorial
Wed, 13 Aug 2003 13:30:01 +0100
> Think of the following though experiment. What if I would have a function
> "unparse:IO a->String" which gives the textual representation of the
> specification of the object of type IO a? Clearly, IO is not a monad
> anymore. Moreover, I don't think it would break the purity of Haskell. And
> surely, in case of the IO monad, we can think of better manners to break a
> program down.
Why would such a function cause IO to cease being a monad?
There's no reason such a function couldn't be written, given an
appropriate implementation of IO, and an implementation that is able
to print a representation of a function (not too difficult for an
interpreter). Imagine adding "deriving Show" to the data types IO and
SysCall suggested by Ross Paterson in