forth: max

Hmmm, in implementing MAX in forth returning the biggest of two number from the stack, there might be several solutions. The simplest and most straightforward is something like:

: max over over < if swap else then drop ;

Not using any type of if/branching/skip instruction it becomes more interesting. Using abs is one possibility http://www.retroprogramming.com/2009/06/implement-min-in-forth-without.html but abs is implemented often by branching (?) and isn't a very primitive first forth word. Instead one can use the fact that conditional less than "<" return 0 if false and -1 otherwise...

Using only simple operators I came up with this, it's kind of overly long but...

: max over over < dup 1 + rot rot * negate rot rot * + ;

3 4 max .

-> 4

4 3 max .

-> 4

I guess one could use < to implement abs similarly and use the simplier definition in the link above, but abs becomes:

: abs dup 0 < 2 * 1 + * ; 

77 3 - abs .

-> 74

3 77 - abs .

-> 74

ok, so then using this abs which isn't too fanicful define min instead (max require an swap somewhere)

: min over over - abs - + 2 / ;

3 4 min .

-> 3

4 3 min .

-> 3

--
.sigh