factorial :: Int -> Int
-- testing 4 combinations of argument values
-- pruning with 27/65 rules
-- 3 candidates of size 1
-- 3 candidates of size 2
-- 7 candidates of size 3
-- 8 candidates of size 4
-- 28 candidates of size 5
-- 35 candidates of size 6
-- 167 candidates of size 7
-- tested 95 candidates
factorial 0  =  1
factorial x  =  x * factorial (x - 1)

factorial :: Int -> Int
-- testing 4 combinations of argument values
-- pruning with 32/72 rules
-- 3 candidates of size 1
-- 3 candidates of size 2
-- 7 candidates of size 3
-- 8 candidates of size 4
-- 28 candidates of size 5
-- 75 candidates of size 6
-- tested 74 candidates
factorial x  =  foldr (*) 1 [1..x]