18 Sep
2013
18 Sep
'13
2:21 p.m.
On Wed, Sep 18, 2013 at 9:08 PM, TP
f :: Foo -> Bool f (Foo n) | even n = True | odd n = False f (Bar n) | even n = True | odd n = False
(1) Since even is monomorphized to Int -> Bool, you can just write f (Foo n) = even n f (Bar n) = even n (2) Since the sum subtypes are the same, you can write data Foo = Foo {myN :: Int} | Bar {myN :: Int} f :: Foo -> Bool f x = even $ myN x (3) As to your original question why the underscore _ can't be overloaded for this, I dunno. It /may/ be possible. Seems rare in practice. You could always apply the type isomorphism to get data FooT = Foo | Bar data Foo = Foo Int FooT f (Foo n _) = even n -- Kim-Ee