On Thu, Apr 15, 2010 at 10:59 PM, zaxis
instance (BinaryDefer a, BinaryDefer b) => BinaryDefer (a,b) where put (a,b) = put2 a b get = get2 (,) size x = let ~(a,b) = x in size a + size b putFixed (a,b) = putFixed2 a b getFixed = getFixed2 (,)
in `size` function, what does the `~` mean ?
This is kind of a funny question, because in this case the ~ doesn't mean anything at all. Pattern matches in let are automatically irrefutable/lazy. A better way to write this is size ~(a,b) = size a + size b which is equivalent to size x = size a + size b where (a,b) = x which is equivalent to size x = let (a,b) = x in size a + size b which is equivalent to size x = let a = case x of (v,_) -> v b = case x of (_,v) -> v in size a + size b If a or b never get evaluated, the case statements (which will fail on bottom values) don't happen.