TST.hs

{-
  This module is part of Antisplice.
  Copyleft (c) 2014 Marvin Cohrs

  All wrongs reversed. Sharing is an act of love, not crime.
  Please share Antisplice with everyone you like.

  Antisplice is free software: you can redistribute it and/or modify
  it under the terms of the GNU Affero General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Antisplice is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
  GNU Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with Antisplice. If not, see <http://www.gnu.org/licenses/>.
-}

-- | Provides a ternary search trie
module Game.Antisplice.Utils.TST where

import Data.Maybe

-- | A ternary search trie
data TST a = EmptyTST | TST Char (Maybe a) (TST a) (TST a) (TST a)

-- | Insert something into the TST
tstInsert :: String -> a -> TST a -> TST a
tstInsert (c:[]) a EmptyTST = TST c (Just a) EmptyTST EmptyTST EmptyTST
tstInsert (c:cs) a EmptyTST = TST c Nothing (tstInsert cs a EmptyTST) EmptyTST EmptyTST
tstInsert cs a (TST c1 a1 f l r)
  | head cs < c1 = TST c1 a1 f (tstInsert cs a l) r
  | head cs > c1 = TST c1 a1 f l (tstInsert cs a r)
  | cs == [c1] = TST c1 (Just a) f l r
  | otherwise = TST c1 a1 (tstInsert (tail cs) a f) l r

-- | Lookup some string in the TST
tstLookup :: String -> TST a -> Maybe a
tstLookup _ EmptyTST = Nothing
tstLookup cs (TST c1 a1 f l r)
  | head cs < c1 = tstLookup cs l
  | head cs > c1 = tstLookup cs r
  | cs == [c1] = a1
  | otherwise = tstLookup (tail cs) f

-- | Check if the TST contains the given key
tstContains :: String -> TST a -> Bool
tstContains cs = isJust . tstLookup cs