Whoops - replied in haste...
There is a long extant GHC extension to elide constructor arguments
f (Leaf {}) = ...
f (Node {}) = ...
There is a recent extension for "lambda case" which you were also
using and I didn't look closely at.
On 5 November 2012 21:11, Stephen Tetley <[email protected]> wrote:
> 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
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