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87 lines
2.8 KiB
Haskell
87 lines
2.8 KiB
Haskell
2 years ago
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module Main where
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import Data.Char
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import qualified Data.Map as M
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data Token = Number Double | ParenOpen | ParenClose | AddOp | MulOp | DivOp | SubOp deriving (Show, Eq)
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isOp:: Token -> Bool
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isOp AddOp = True
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isOp MulOp = True
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isOp DivOp = True
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isOp SubOp = True
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isOp _ = False
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scanNumber:: String -> (Double, String)
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scanNumber xs = (num, str) where
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(n, str) = span isNumber xs
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num = read n :: Double
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opmap:: M.Map Char Token
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opmap = M.fromList [ ('+', AddOp), ('*', MulOp), ('/', DivOp), ('(', ParenOpen), ('-', SubOp), (')', ParenClose)]
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tokenize:: String -> [Maybe Token]
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tokenize s = loop s [] where
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loop str tokens
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| null str = tokens
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| isNumber $ head str = let
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(num, str') = scanNumber str
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tokens' = tokens ++ [Just (Number num)]
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in loop str' tokens'
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-- Skip whitespaces
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| (\c -> c == ' ') $ head str = loop (tail str) tokens
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-- Otherwise lookup for op
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| otherwise = loop (tail str) (tokens ++ [M.lookup (head str) opmap])
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opPriority :: Token -> Int
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opPriority AddOp = 0
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opPriority SubOp = 0
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opPriority MulOp = 1
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opPriority DivOp = 1
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opPriority ParenOpen = 2
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opPriority ParenClose = 2
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opPriority (Number _) = 3
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-- Shunting yard algo
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transform:: [Maybe Token] -> [Token]
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-- tokens - stack - output
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transform ts = transform' ts [] [] where
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transform' [] [] q = q
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transform' [] s q =
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if head s == ParenOpen
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then error "Mismatched parentheses"
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else transform' [] (tail s) (q ++ [head s])
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transform' (x:xs) s q = case x of
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Nothing -> error "Illegal tokens"
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(Just (Number n)) -> transform' xs s (q ++ [Number n])
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(Just ParenOpen) -> transform' xs (ParenOpen:s) q
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(Just ParenClose) -> transform' xs s0 q0 where
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s0 = tail $ dropWhile (/= ParenOpen) s
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q0 = q ++ takeWhile (/= ParenOpen) s
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(Just o1) -> transform' xs s1 q1 where
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cond o2 = isOp o2 && (opPriority o1 < opPriority o2)
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spl = span cond s
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s1 = o1 : snd spl
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q1 = q ++ fst spl
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eval :: [Token] -> Token
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eval ts = head $ eval' [] ts where
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eval' :: [Token] -> [Token] -> [Token]
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eval' st (t:ts) = let
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numFromToken (Number n) = n
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fstNum = numFromToken . head
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sndNum = numFromToken . head . tail
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rem = tail . tail
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in case t of
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Number n -> eval' (t : st) ts
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AddOp -> eval' ((Number (fstNum st + sndNum st)) : (rem st)) ts
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MulOp -> eval' ((Number (fstNum st * sndNum st)) : (rem st)) ts
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DivOp -> eval' ((Number (sndNum st / fstNum st)) : (rem st)) ts
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SubOp -> eval' ((Number (sndNum st - fstNum st)) : (rem st)) ts
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eval' st [] = st
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main = do
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s <- getLine
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let Number res = eval $ transform $ tokenize s
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print res
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