39 lines
1.2 KiB
Haskell
39 lines
1.2 KiB
Haskell
module Main (main) where
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import Text.Parsec
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import Lib (exprparser, evaluate, replaceVars, Expr)
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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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main :: IO ()
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main = ioLoop
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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 :: Either ParseError Expr -> String
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useResult (Right expr) = either id ((showRatio precision) . evaluate) $ replaceVars expr vars
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useResult (Left error) = show error
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vars :: Map String Rational
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vars = Map.fromList [("pi", 245850922 % 78256779), ("e", 271801 % 99990)]
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ioLoop :: IO ()
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ioLoop = 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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putStrLn . useResult $ expr
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ioLoop
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