40 lines
1.4 KiB
Haskell
40 lines
1.4 KiB
Haskell
module Main (main) where
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import Text.Parsec
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import Lib (exprparser, evaluate, replaceVars, Expr, extractVariableDefinitions)
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import Data.Map (Map)
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import qualified Data.Map as Map
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import Data.Ratio
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import System.IO
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initVars :: Map String Rational
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initVars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]
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main :: IO ()
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main = ioLoop initVars
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precision = 5 :: Int
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showRatio :: Int -> Rational -> String
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showRatio p r = (if (r < 0) then "-" else "") ++ prepoint_digits ++ (if (length postpoint_digits > 0) then ("." ++ postpoint_digits) else "")
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where
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prepoint_digits = init . show . round . abs $ (r * 10)
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postpoint_digits = reverse . dropWhile (=='0') . reverse .(take p) . (drop (length prepoint_digits)) . show . round . abs $ (r * 10^p)
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useResult :: Map String Rational -> Either ParseError Expr -> String
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useResult vs (Right expr) = either id ((showRatio precision) . evaluate) $ replaceVars expr vs
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useResult vs (Left error) = show error
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ioLoop :: Map String Rational -> IO ()
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ioLoop vs = do done <- isEOF
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if done
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then putStrLn "Quit!"
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else do inp <- getLine
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let expr = parse exprparser "<stdin>" inp
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let uvs = either (const vs) (\e -> Map.unionWith (flip const) vs (extractVariableDefinitions e)) expr
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putStrLn $ useResult uvs expr
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ioLoop uvs
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