[Haskell-cafe] Point-free style in guards

[Luke Palmer]

2008/7/22 J.N. Oliveira <jno at di.uminho.pt>:
> But you still need the extra parentheses...

Not so!

infixl 0 .|
infixl 0 .|...  -- 'otherwise' construct
infix 1 .=

(.=) :: (a -> Bool) -> (a -> b) -> (a -> Maybe b)
(.|) :: (a -> Maybe b) -> (a -> Maybe b) -> (a -> Maybe b)
(.|...) :: (a -> Maybe b) -> (a -> b) -> (a -> b)
-- implementations left as exercise for the reader

outStanza = isMessage .= outMessage
         .| isPresence .= outPresence
         .| isIQ       .= outIQ
         .|...            const 42

Hooray for abusing operators!

Luke