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{- This is a simple factorial program which uses the I/O system
to read the input and print the result -}
module Main where
fact :: Integer -> Integer
fact 0 = 1
fact (n+1) = (n+1)*fact n
fact _ = error "Negative argument to factorial"
main = appendChan stdout "Type in N: " abort $
readChan stdin abort $ \ input ->
appendChan stdout (show (fact (read (head (lines input))))) abort done
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