+-- | foldl function identifier
+foldlId :: String
+foldlId = "foldl"
+
+-- | foldr function identifier
+foldrId :: String
+foldrId = "foldr"
+
+-- | zip function identifier
+zipId :: String
+zipId = "zip"
+
+-- | unzip function identifier
+unzipId :: String
+unzipId = "unzip"
+