64 lines
1.6 KiB
Haskell
64 lines
1.6 KiB
Haskell
{-# LANGUAGE ViewPatterns #-}
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import Data.List
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import Data.Maybe
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import Text.Read
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import Text.Printf
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import Control.Monad
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import System.Console.Readline
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main :: IO ()
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main = do
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line <- readline "ꟼ "
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case fromMaybe "" line of
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"" -> main
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"q" -> return ()
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exp -> do
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putStrLn $ result (rpn exp) ++ "\n"
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addHistory exp
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main
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-- Pretty print RPN result/errors
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result :: Either String Double -> String
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result (Left err) = "Ꞥ∘ " ++ err
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result (Right x) = printf format x where
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format | ceiling x == floor x = "∘ %.0f"
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| otherwise = "∘ %.10f"
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-- Solve a RPN expression
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rpn :: String -> Either String Double
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rpn = foldM parse [] . words >=> return . head where
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parse (y:x:xs) (flip lookup dyad -> Just f) = Right (f x y : xs)
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parse (x:xs) (flip lookup monad -> Just f) = Right (f x : xs)
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parse xs (flip lookup nilad -> Just k) = Right (k : xs)
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parse xs (readMaybe -> Just x) = Right (x : xs)
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parse _ _ = Left "syntax error"
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-- dyadic functions
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dyad = [ ("+", (+))
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, ("-", (-))
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, ("*", (*))
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, ("/", (/))
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, ("^", (**)) ]
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-- monadic functions
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monad = [ ("sin" , sin )
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, ("asin" , asin)
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, ("cos" , cos )
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, ("acos" , acos)
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, ("tan" , tan )
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, ("atan" , atan)
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, ("ln" , log )
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, ("sqrt" , sqrt)
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, ("sgn" , signum)
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, ("abs" , abs)
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, ("floor", fromIntegral . floor)
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, ("ceil" , fromIntegral . ceiling) ]
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-- niladic functions
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nilad = [ ("pi" , pi)
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, ("e" , exp 1)
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, ("phi", (1 + sqrt 5)/2) ] |