[Haskell-cafe] Identity of indiscernibles
tom-lists-haskell-cafe-2013 at jaguarpaw.co.uk
Thu Aug 8 18:48:00 CEST 2013
On Thu, Aug 08, 2013 at 05:44:11PM +0100, Tom Ellis wrote:
> 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)
I suppose that should actually be 'csin :: CDouble -> IO CDouble', but
hopefully the general method is clear.
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