Define concat in terms of foldr

Data/SBV/List.hs

@@ -536,13 +536,10 @@ zipWith f xs ys
 
 -- | Concatenate list of lists.
 --
--- NB. Concat is typically defined in terms of foldr. Here we prefer foldl, since the underlying solver
--- primitive is foldl: Otherwise, we'd induce an extra call to reverse.
---
 -- >>> concat [[1..3::Integer], [4..7], [8..10]]
 -- [1,2,3,4,5,6,7,8,9,10] :: [SInteger]
 concat :: SymVal a => SList [a] -> SList a
-concat = foldl (++) []
+concat = foldr (++) []
 
 -- | Check all elements satisfy the predicate.
 --