Nested HashMap implementation.

NestedHashMap.hs

module NestedHashMap where

import Control.Lens
import Data.Hashable       (Hashable)
import Data.HashMap.Strict (HashMap, empty)

type NestedHashMap a b c = HashMap a (HashMap b c)

lookup
    :: (Eq a, Hashable a, Eq b, Hashable b, Eq c)
    => a -> b -> NestedHashMap a b c -> Maybe c
lookup k k' hash = hash ^.at k . non empty ^.at k'

-- Insert a value. Creating top level key if one does not exist.
insert
    :: (Eq a, Hashable a, Eq b, Hashable b, Eq c)
    => a -> b -> c -> NestedHashMap a b c -> NestedHashMap a b c
insert k k' v hash = hash & at k . non empty . at k' ?~ v

-- Delete a key. Deleting top level key if it is empty after delete.
delete
    :: (Eq a, Hashable a, Eq b, Hashable b, Eq c)
    => a -> b -> NestedHashMap a b c -> NestedHashMap a b c
delete k k' hash = hash & at k . non empty . at k' .~ Nothing