On Tuesday, May 13, 2014, Dirk Laurie <
dirk.laurie@gmail.com> wrote:
2014-05-14 2:40 GMT+02:00 Andrew Starks <andrew.starks@trms.com>:
> I don't have my mind around this, but I'm trying...
>
> Is it something like: "these are still individual captures, but for the
> purposes of numbering, they're grouped, which makes it possible to specify a
> subset of captures from a set."
### Group and back captures
These patterns are useless by themselves. They are always used as
part of a bigger pattern.
The first version of this document said: "The remaining capture
functions: `Cg` and `Cb`, are definitely too advanced for this primer."
That is still basically true, but one application is within reach:
the Group-Back combination allows values to be stored and retrieved.
__`Cg(p,name), p:Cg(name)`__ (Group)
~ Collects all the captures `p` made into a single entity, and gives
that entity a name for future reference. Does not actually add any
captured values to the big pattern.
__`Cb(name)`__ (Back)
~ Retrieves the entity with the given name, and supplies
its captures to the big pattern.
> An example in the LPeg doc or a clarifying disclaimer would have been
> appreciated, but your answer is great too!
The above quote is from
<https://github.com/dlaurie/lua-notes/blob/master/lpeg-brief.txt>
which explains LPeg from the point of a newbie who has just reached
the point where things start to make sense.
I read through your document. I like the idea of a promise to refrain from editing, once you're smarter. :)
I use Cg with Ct and Cb every now-and-again. I was speaking more to anonymous version and the meaning of "grouping the values of multiple captures into a single capture" and what it's good for.
-Andrew
