foldl1 +base

foldl1 :: (a -> a -> a) -> [a] -> a
base Prelude, base Data.List
foldl1 is a variant of foldl that has no starting value argument, and thus must be applied to non-empty lists.
foldl1 :: Foldable t => (a -> a -> a) -> t a -> a
base Data.Foldable
foldl1' :: (a -> a -> a) -> [a] -> a
base Data.List
A strict version of foldl1