Re: [Haskell-cafe] Partial application in case expression rules

There's a Glasgow extension that gets you to this: treeFold :: (a -> a -> a) -> Tree a -> a treeFold f = \case Leaf {} -> id Node {} -> f `on` treeFold f Or maybe this if parens are needed: treeFold :: (a -> a -> a) -> Tree a -> a treeFold f = \case (Leaf {}) -> id (Node {}) -> f `on` treeFold f