hc/app/Main.hs

module Main (main) where

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

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 -> Expr -> String
useResult vs expr = either id ((showRatio precision) . evaluate) $ replaceVars expr vs

ioLoop :: Map String Rational -> IO ()
ioLoop vs = do done <- isEOF
               if done
                 then putStrLn "Quit!"
                 else do inp <- getLine
                         let expr_res = parseFullString inp
                         case expr_res of
                             Left err   -> do
                                 putStrLn . show $ err
                                 ioLoop vs
                             Right expr -> do
                                 let vardefs = extractVariableDefinitions expr
                                 let uvs_res = updateVariables vardefs vs
                                 case uvs_res of
                                     Left  err -> putStrLn err
                                     Right uvs -> putStrLn $ useResult uvs expr
                                 ioLoop (either (const vs) (id) uvs_res)