Re: [Haskell-cafe] selectively allow alternatives in a sum type

On 01-09-22 16:33, Dominik Schrempf wrote:

Chiming in here, maybe I missed something. Liquid Haskell is great, but in this case, in my opinion, easier is better:

newtype LeftFoo = LeftFoo !Int

newtype RightFoo = RightFoo !Char

data Foo = LFoo LeftFoo | RFoo RightFoo – Probably with strictness annotations.

isLeftFoo :: Foo -> Bool isLeftFoo (LFoo _) = True isLeftFoo _ = False

takesOnlyLeftFoo :: LeftFoo -> Int takesOnlyLeftFoo (LeftFoo i) = i

Dominik

Chiming in here too. I do this all the time if the subpart is to be used on 2 or more places. Easiest way to do this without extensions. -- Rubén. (pgp: 1E88 3AC4 89EB FA22)