import "Prelude" as Prelude
import "MMap" as MMap
import "MList" as MList

type T a b = MMap.T a (MList.T b)

add :: MMap.T a (MList.T b) -> a -> b -> <Proc> ()
add m k v = match MMap.get m k with
    Just l -> MList.add l v
    Nothing -> Prelude.ignore (MMap.put m k (MList.singleton v))

get :: MMap.T a (MList.T b) -> a -> <Proc> [b]
get m k = match MMap.get m k with
    Just l -> MList.freeze l
    Nothing -> []

indexBy :: (v -> <e> k) -> [v] -> <Proc,e> MMap.T k (MList.T v)
indexBy f l = do
    result = MMap.createC (Prelude.length l)
    Prelude.iter (\v -> add result (f v) v) l
    result