data-map-multikey

Data.Map, but indexed by multiple, unique keys.

This small project came out of exploring the code for IxSet. It's essentially IxSet without the Sets, and hence without the ability to support duplicate keys. On the upside, it's small and easy to understand.

Example

{-# LANGUAGE DeriveDataTypeable #-}

module Main where

import Data.Map.MultiKey
import Data.Typeable
import Prelude hiding (lookup, null)

data Record = Record
  { rIntKey :: Int
  , rStringKey :: String
  , rData :: String
  } deriving (Show, Typeable)

instance MultiKeyable Record where 
  empty = MultiKey [key rIntKey, key rStringKey]

records :: [Record]
records =
  [ Record 1 "key 1" "data 1"
  , Record 20 "key 20" "data 20"
  , Record 3 "key 3" "data 3"
  ]

mk :: MultiKey Record
mk = fromList records

{-
> lookup (1::Int) mk
Just (Record {rIntKey = 1, rStringKey = "key 1", rData = "data 1"})
it :: Maybe Record

> lookup "key 20" mk
Just (Record {rIntKey = 20, rStringKey = "key 20", rData = "data 20"})
it :: Maybe Record

> lookup 2.0 mk
*** Exception: MultiKey: there is no key of type Double in MultiKey Record
-}

sclausen/data-map-multikey

data-map-multikey

Example