augment -fgl +base

augment :: (forall b. (a -> b -> b) -> b -> b) -> [a] -> [a]
base GHC.Exts
A list producer that can be fused with foldr. This function is merely > augment g xs = g (:) xs but GHC's simplifier will transform an expression of the form foldr k z (augment g xs), which may arise after inlining, to g k (foldr k z xs), which avoids producing an intermediate list.