simonpj's proposal on guards:
> > I would really welcome feedback on this proposal. Have you encountered
> > situations in which pattern guards would be useful? Can you think of ways
> > in which they might be harmful, or in which their semantics is non-obvious?
> > Are there ways in which the proposal could be improved? And so on.
M. Chakravarty:
> ... The proposed syntax may look a bit strange in the beginning,
> but I find the upward compatibility and the simple changes to the
> grammar very attractive.
after some thought, the syntax looks just right for me. after all,
the proposal could be read as transforming
fun x | Just b <- ..., more guards = expression
into
fun x = do { Just b <- ..., more guards, return expression }
which makes sense since this is really happening in the
underlying (identity) monad.
in fact it's not the identity but it
also has a zero (pattern doesn't match)
and a (++) (if left arg. fails, try right arg.)
as in
fun x | guardx = ...; fun y | guardy = ...
which "really" is
fun = (\ x -> do { guardx, return ...} )
++ (\ y -> do { guardy, return ...} )
--
Johannes Waldmann Institut für Informatik FSU D-07740 Jena Germany
http://www5.informatik.uni-jena.de/~joe/ mailto:[EMAIL PROTECTED]
