Re: Lpeg: a question about function captures and named captures

[Sean Conner <sean@...>]

It was thus said that the Great Andrew Gierth once stated:
> >>>>> "Sean" == Sean Conner <sean@conman.org> writes:
> 
>  >> > (Cc"a" * Cc"b" / f):Cg"c" :ptmatch("ccc")
>  >> {"c"="ab"}
>  >> 
>  >> How do I modify the ".../f" above to make it put the first result of f
>  >> into :Cg"c" and the second result into :Cg"d"?
> 
>  Sean> If I understand your question correctly, for
> 
>  Sean> 	Cc'a' * Cc'b' / f
> 
>  Sean> you want the first result of f() to go into a field named 'c',
>  Sean> and the second result of f() to go into a field named 'd'. Yes,
>  Sean> that isn't going to work.
> 
> Well... sorta.
> 
> ((Cc"a" * Cc"b" / f):Cg"c" * (Cb"c" / 2):Cg"d"):ptmatch("ccc");

  This is hurting my brain.  It just doesn't look right to me, as I would
write this as:

	Ct(
	      Cg(Cc"a" * Cc"b" / f , 'c')
	    * Cg(Cb"c" / 2,          'd')
	)

> This puts the list of captures returned by f into named capture "c", and
> then extracts the second one into "d" by using a back capture. When Ct()
> is applied to the result, only the first value of "c" is used, so the
> result is { c="ab", d="ba" }.

  I'll admit, I'm surprised!  I haven't used "pattern / number" in any LPEG
code I've written so far.  

> Note, though, that in my tests (on 5.3) this ended up evaluating f()
> twice 

  I think this is more on the LPEG version and less on the Lua version.  

  -spc