factorial :: Int -> Int
-- testing 6 combinations of argument values
-- looking through 2/6 candidates of size 1
-- looking through 2/4 candidates of size 2
-- looking through 0/6 candidates of size 3
-- looking through 2/10 candidates of size 4
factorial n  =  product (enumFromTo 1 n)

factorial :: Int -> Int
-- testing 6 combinations of argument values
-- looking through 3/9 candidates of size 1
-- looking through 5/14 candidates of size 2
-- looking through 8/26 candidates of size 3
-- looking through 26/66 candidates of size 4
-- looking through 59/180 candidates of size 5
-- looking through 167/505 candidates of size 6
-- looking through 581/1521 candidates of size 7
-- looking through 1654/4809 candidates of size 8
-- looking through 5736/15120 candidates of size 9
-- looking through 17617/48943 candidates of size 10
factorial n  =  if n == 0 then 1 else n * factorial (dec n)