{-
- The Lambda Shell, an interactive environment for evaluating pure untyped lambda terms.
- Copyright (C) 2005-2011, Robert Dockins
-
- This program is free software; you can redistribute it and/or modify
- it under the terms of the GNU General Public License as published by
- the Free Software Foundation; either version 2 of the License, or
- (at your option) any later version.
-
- This program 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 General Public License for more details.
-
- You should have received a copy of the GNU General Public License
- along with this program; if not, write to the Free Software
- Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
-}
module Env
( Env
, empty
, insert
, lookup
) where
import Prelude hiding (lookup)
import qualified Data.Set as Set
data Env = Env !Int ![String] !(Set.Set String)
empty :: Set.Set String -> Env
empty = Env 0 []
insert :: String -> Env -> Env
insert label (Env z labels set)
| label `Set.member` set = Env (z+1) ( (label++"_"++(show z)) : labels) set
| otherwise = Env z ( label : labels ) (Set.insert label set)
lookup :: Int -> Env -> String
lookup x (Env z labels set) =
case drop x labels of
l:_ -> l
[] -> error (concat ["'",show x,"' out of bounds in environment ",show labels])