:: a -> [(a, b)] -> b package:base-prelude

lookup :: Eq a => a -> [(a, b)] -> Maybe b
base-prelude BasePrelude
lookup key assocs looks up a key in an association list. 
>>> lookup 2 []
Nothing

>>> lookup 2 [(1, "first")]
Nothing

>>> lookup 2 [(1, "first"), (2, "second"), (3, "third")]
Just "second"