factorial :: Int -> Int
-- testing 6 combinations of argument values
-- looking through 2 candidates of size 1
-- looking through 2 candidates of size 2
-- looking through 0 candidates of size 3
-- looking through 2 candidates of size 4
factorial n  =  product (enumFromTo 1 n)

factorial :: Int -> Int
-- testing 6 combinations of argument values
-- looking through 3 candidates of size 1
-- looking through 5 candidates of size 2
-- looking through 8 candidates of size 3
-- looking through 26 candidates of size 4
-- looking through 59 candidates of size 5
-- looking through 167 candidates of size 6
-- looking through 581 candidates of size 7
-- looking through 1654 candidates of size 8
-- looking through 5754 candidates of size 9
-- looking through 17797 candidates of size 10
factorial n  =  if n == 0 then 1 else n * factorial (dec n)