[Haskell-cafe] Identity of indiscernibles

[Tom Ellis]

On Thu, Aug 08, 2013 at 06:25:12PM +0200, Daniel Trstenjak wrote:
> > See [1] 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)

Tom