Possible regression with the Traversable instance of Vec about clash-prelude

[christiaanb]

For clash-prelude-0.10 we changed the Foldable (and consequently the Traversable) instance so that it only works for non-empty Vectors. Basically, you will have to change foo to:

foo :: KnownNat n => Maybe (Vec (n + 1) Int) -> Foo (n + 1)
foo v = Foo $ v >>= traverse bar

Maybe the following also works.

foo :: (KnownNat n, 1 <= n) => Maybe (Vec n Int) -> Foo n
foo v = Foo $ v >>= traverse bar

I blame this on Foldable being a rediculously large type-class, and including foldr1 and foldl1, which can only be reasonably implemented for non-empty Vectors.

[pikkio]

Oh, I see. Thank you very much!
Even though it's a little bit more verbose, the following code compiles perfectly:

{-# LANGUAGE DataKinds        #-}
{-# LANGUAGE KindSignatures   #-}
{-# LANGUAGE TypeOperators    #-}
{-# LANGUAGE FlexibleContexts #-}

import CLaSH.Sized.Vector (Vec (..))
import GHC.TypeLits       (KnownNat, Nat, type (+))

foo :: KnownNat (n + 1) => Maybe (Vec (n + 1) Int) -> Foo (n + 1)
foo v = Foo $ v >>= traverse bar

-- etc.