[Haskell-cafe] Identity of indiscernibles
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk
Thu Aug 8 18:05:58 CEST 2013
On Thu, Aug 08, 2013 at 03:38:41PM +0200, Jerzy Karczmarczuk wrote:
> >One could simply implement IO as a free monad
> Interesting. I wonder how.
See  for an explanation of free monads in general. For IO in particular,
define a functor
data IOF a = GetChar (Char -> a) | PutChar Char a | ...
with constructors for all elementary IO operations. Then take
type IO a = Free IOF a
getChar :: IO Char
getChar = liftF (GetChar id)
putChar :: Char -> IO ()
putChar c = liftF (PutChar c ())
etc.. I make no claims about the performance of a runtime system based on
suhc a representation!
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