Re: LPeg and function capture

[Roberto Ierusalimschy <roberto@...>]

> Posting in the same thread, as it is related to my experiments.
> I am puzzled by a result I got.
> This works as expected:
> 
> local cap = m.R'AZ'
> local findCap = (1 - cap) + m.C(cap)
> local toMatch = "Stairway To Heaven"
> local patt = findCap^0 / function (a, b, c)
>   return string.lower(a .. b .. c)
> end
> print(m.match(patt, toMatch))
> 
> But the following doesn't, the function gets all chars, not only the
> capital ones (those supposed to be captured):
> 
> local patt = (findCap / function (a) return string.lower(a) end)^0
> print(m.match(patt, toMatch))
> 
> Why the behavior of the pattern is changed by the associated function?

In all cases, the function is called once everytime there is a match.
In the second case, there is match for each character (because of the
(1 - cap) in 'findCap').  When the pattern of a function capture
produces no captures, the entire match is given as the captured value.

Maybe this is what you whant:

local findCap = (1 - cap) + m.C(cap) / string.lower

Now the function is called only when 'm.C(cap)' matches.

-- Roberto