[Haskell-cafe] Identity of indiscernibles
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk
Thu Aug 8 18:44:11 CEST 2013
On Thu, Aug 08, 2013 at 06:25:12PM +0200, Daniel Trstenjak wrote:
> > 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.
> But how should this work if the user adds an IO operation, e.g by wrapping a C function?
Wrapping a C function could perhaps be provided by something like
data IOF a = ... | forall i o. Foreign String i (o -> a) | ...
csin :: Double -> IO Double
csin x = liftF (Foreign "math.h sin" x id)
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