23 lines
607 B
Haskell
23 lines
607 B
Haskell
{-# LANGUAGE FlexibleContexts #-}
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import Control.Applicative (Applicative((<*>), (*>)), (<$>))
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import Text.Parsec
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expandRange :: String -> Maybe [Int]
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expandRange = either (const Nothing) Just . parse rangeParser ""
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rangeParser
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:: (Enum a, Read a, Stream s m Char)
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=> ParsecT s u m [a]
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rangeParser = concat <$> (item `sepBy` char ',')
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where
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item = do
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n1 <- num
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n2 <- option n1 (char '-' *> num)
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return [n1 .. n2]
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num = read `dot` (++) <$> option "" (string "-") <*> many1 digit
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dot = (.) . (.)
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main :: IO ()
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main = print $ expandRange "-6,-3--1,3-5,7-11,14,15,17-20"
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