extend :: (Ord k) => Map k v -> [(k,v)] -> Map k v
extend = foldl' ins
  where ins m (k,v) = insert k v m
extend :: (Ord k) => Map k v -> [(k,v)] -> Map k v
extend = foldl' ins
  where ins m (k,v) = insert k v m
extend = foldl' ins
  where ins m (k,v) = insert k v m