LPeg: inserting previous captures by substitution

[Александр Машин <alex.mashin@...>]

> Use this:
> integer <- { int } int <- {~ digits spaces -> '' int / digits ~}
> That gives you two captures, the first is the unmodified
> (unsubstituted) match:
> print(patt:match("6 000 000")) -->  6 000 000 6000000
Thank you, Mr Donnelly, but I am trying to do it with pure re, while 
concatenating two captures will require outer Lua code.

I am looking for something like %1 in the second argument of string.gsub 
(). For something like =name but usable after ->.

Alexander Mashin