stack based languages

Hello, i am interested in learning a stack oriented language, so i started learning Forth. (from http://www.amresearch.com/starting_forth/)
Some alternatives i heard of are cat and factor.

What is best to learn from those? And suggest a good tutorial

>>12
fib(x) = lambda x if x < 2 else fib(x - 1) + fib(x - 2)
That was seriously fucked up, copypasted bits of the def one and failed it.

fib = lambda x: x if x < 2 else fib(x - 1) + fib(x - 2)