husky-0.1: src/CalculatorState.hs

{-----------------------------------------------------------------
 
  (c) 2008-2009 Markus Dittrich 
 
  This program is free software; you can redistribute it 
  and/or modify it under the terms of the GNU General Public 
  License Version 3 as published by the Free Software Foundation. 
 
  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 Version 3 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., 59 Temple Place - Suite 330, 
  Boston, MA 02111-1307, USA.

--------------------------------------------------------------------}

-- | this module contains small bits and pieces needed for 
-- the calculator. Eventually, these might all find a home
-- in their separate modules
module CalculatorState ( CalcState(..)
                       , defaultCalcState 
                       , insert_variable
                       ) where


-- imports
import qualified Data.Map as M


-- | this data structure provides some state information
-- to the calculator (variables, etc ...)
data CalcState = CalcState { varMap :: M.Map String Double }

defaultCalcState :: CalcState
defaultCalcState = CalcState { varMap = M.fromList constantList }


-- | function adding a new variable to the database
insert_variable :: Double -> String -> CalcState -> CalcState
insert_variable num name (CalcState { varMap = theMap }) =
    CalcState { varMap = M.insert name num theMap } 



-- | provide a few useful mathematical constants that we
-- load into the default CalculatorState
constantList :: [(String,Double)]
constantList = 
    [ ("pi",3.14159265358979323846264338327950288)
    , ("e",2.71828182845904523536028747135266249)
    , ("phi",1.61803398874989484820458683436563811)]  -- golden ratio