42 lines
1.0 KiB
Haskell
42 lines
1.0 KiB
Haskell
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{-# LANGUAGE ViewPatterns #-}
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import Data.List
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main :: IO ()
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main = io (show . rpn)
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io :: (String -> String) -> IO ()
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io f = interact (unlines . map f . lines)
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rpn :: String -> Double
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rpn = head . foldl parse [] . words where
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parse (y:x:xs) (flip lookup dyad -> Just f) = f x y : xs
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parse (x:xs) (flip lookup monad -> Just f) = f x : xs
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parse xs (flip lookup nilad -> Just k) = k : xs
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parse xs x = read x : xs
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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) ]
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