mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-20 10:02:03 +03:00
14 lines
419 B
Idris
14 lines
419 B
Idris
interface Decidable p where
|
|
decide : Either p (Not p)
|
|
|
|
{m, n : Nat} -> Decidable (m === n) where
|
|
decide = go m n where
|
|
|
|
go : (m, n : Nat) -> Either (m === n) (Not (m === n))
|
|
go 0 0 = Left Refl
|
|
go 0 (S k) = Right (\case Refl impossible)
|
|
go (S k) 0 = Right (\case Refl impossible)
|
|
go (S k) (S j) = case go k j of
|
|
Left eq => Left (cong S eq)
|
|
Right neq => Right (\case Refl => neq Refl)
|