Repeated letters in ggg

[WarpedWartWars]

Regular expressions have a way to do this, for example (whatever*) matches "whateverwhateverwhatever", "whatever", etc., but not "whatevre", "waeehtvr", "qwertyuiopasdfghjklzxcvbnm", etc. Is there a way to do this in ggg?

[zompist]

As stated, sure:

S=W
W=W W|whatever

I'm guessing you mean something more complicated than this, but I'm not sure what!

[WarpedWartWars]

What I specifically want it for is an extended version of the Math Expressions example. I want it to turn "gggggggg" into "g⁸", "ff" into "f²" etc. Not generating them, but rather collapsing them.