You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
20 lines
476 B
Haskell
20 lines
476 B
Haskell
module Main where
|
|
|
|
factorial :: Integer -> Either String Integer
|
|
factorial n = if n < 0 then
|
|
Left "n cannot be negative"
|
|
else Right $ factorial' n 1 where
|
|
factorial' 0 res = res
|
|
factorial' n res = factorial' (n - 1) $! n * res
|
|
|
|
main :: IO()
|
|
main = do
|
|
s <- getLine
|
|
let n = (read s :: Integer)
|
|
let res = factorial n
|
|
case res of
|
|
Right r -> do
|
|
print r
|
|
Left err -> do
|
|
putStrLn $ "Error: " ++ err
|