On Monday 01 November 2004 23:40, Jon Fairbairn wrote:
if Circle.destruct:: Shape -> (Double -> t) -> t -> t and similarly Square.destruct, we'd just have to write the case as
Circle.destruct s f (Square.destruct s g (error "impossible"))
ie the .destructs take a Shape, a function to apply if it matches and a value to return if it doesn't.
Ah, I see. It's rather more ugly but it is a better match for what Haskell does at the moment, isn't it? (IIRC patterns are matched in the order they appear in the source).
Apart from matching up with the names there's not much to choose between one destructor and many, except possibly when one considers something like:
case e of Square s -> ... _ -> ...
particularly if the type has more than two constructors.
True. Anyway, we don't really want to abandon pattern matching syntax, do we? Ben