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20 lines
475 B
Haskell
20 lines
475 B
Haskell
2 years ago
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module Main where
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factorial :: Integer -> Either String Integer
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factorial n = if n < 0 then
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Left "n cannot be negative"
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else Right $ factorial' n 1 where
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factorial' 0 res = res
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factorial' n res = factorial' (n - 1) $ n * res
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main :: IO()
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main = do
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s <- getLine
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let n = (read s :: Integer)
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let res = factorial n
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case res of
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Right r -> do
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print r
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Left err -> do
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putStrLn $ "Error: " ++ err
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