hc/app/Main.hs

--  hc - haskell command line calculator using rational numbers
--  Copyright (C) 2024 VegOwOtenks
--
--  This program 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.
--
--  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 Affero General Public License for more details.
--
--  You should have received a copy of the GNU Affero General Public License
--  along with this program.  If not, see <https://www.gnu.org/licenses/>.
--
--  contact me via vegowotenks at jossco dot de
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)