59 lines
1.5 KiB
Haskell
59 lines
1.5 KiB
Haskell
{-# LANGUAGE ViewPatterns #-}
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import Data.List
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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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main :: IO ()
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main = io (result . rpn)
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-- Interact line-by-line
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io :: (String -> String) -> IO ()
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io f = interact (unlines . map f . filter (not . null) . lines)
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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 ("ꟼ∘ " ++ format) x where
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format = if ceiling n == floor n then "%.0f" else "%.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 x = case readMaybe x of
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Just x -> Right (x : xs)
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Nothing -> 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) ] |