hc/app/Main.hs

module Main (main) where

import Text.Parsec

import Lib (exprparser, evaluate, replaceVars, Expr, extractVariableDefinitions)

import Data.Map (Map)
import qualified Data.Map as Map
import Data.Ratio

import System.IO

initVars :: Map String Rational
initVars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]

main :: IO ()
main = ioLoop initVars

precision = 5 :: Int

showRatio :: Int -> Rational -> String
showRatio p r = (if (r < 0) then "-" else "") ++ prepoint_digits ++ (if (length postpoint_digits > 0) then ("." ++ postpoint_digits) else "")
    where
    	prepoint_digits  = init . show . round . abs $ (r * 10)
	postpoint_digits = reverse . dropWhile (=='0') . reverse .(take p) . (drop (length prepoint_digits)) . show . round . abs $ (r * 10^p)

useResult :: Map String Rational -> Either ParseError Expr -> String
useResult vs (Right expr)  = either id ((showRatio precision) . evaluate) $ replaceVars expr vs
useResult vs (Left  error) = show error

ioLoop :: Map String Rational -> IO ()
ioLoop vs = do done <- isEOF
               if done
                 then putStrLn "Quit!"
                 else do inp <- getLine
                         let expr = parse exprparser "<stdin>" inp
			 let uvs  = either (const vs) (\e -> Map.unionWith (flip const) vs (extractVariableDefinitions e)) expr
                         putStrLn $ useResult uvs expr
                         ioLoop uvs