The fastest way to implement an Dictionary in Haskell

-- Similar in Java, Function f = a -> Maybe b
-- type is just synosym for b -> Maybe b
type Dict a b = a -> Maybe b

insertDict::(Eq k) => k -> v -> Dict k v -> Dict k v
insertDict k v dict = \k' -> k' == k then Just v else dict k'

emptyDict::Dict k v
emptyDict = \_ -> Nothing

-- create empty Dictionary
let dict = emptyDict

-- insert elements to our Dictionary, we can chain them
insertDict 1 "v1" $ insertDict 2 "v2" dict 
print 1 dict => "v1"
print 2 dict => "v2"