Plan 9 from Bell Labs’s /usr/web/sources/contrib/fernan/nhc98/src/prelude/PreludeList/Foldr1.hs
module Prelude where foldr1 :: (a -> a -> a) -> [a] -> a foldr1 f [x] = x foldr1 f (x:xs) = f x (foldr1 f xs) foldr1 _ [] = error "PreludeList.foldr1: empty list"
