Permutations in Stack Programming

dip, drop, dup, and swap are sufficient to perform any manipulation, but permutation literals (using cycle notation) may be more agreeable.

Consider:

rot : a b c -- b c a
    := [ [swap] dip swap ]

This is a shuffle word in Factor.

rot : a b c -- b c a
    := [ (123) ]

It is hardly worth naming when we have permutation literals! Indeed, swap can be defined like so:

swap : a b -- b a
     := [ (12) ]

For shuffle words involving dup, permutation literals may make an implementation easier to conceive.

pick : a b c -- a b c a
     := [ [[dup] dip] dip rot ]

vs.

pick : a b c -- a b c a
     := [ (13) dup (24) ]