Re: help with lpeg

[Wesley Smith <wesley.hoke@...>]

> I want both <length> and <name> to conform to kv as above, but I also
> want the captured value of <length> to conform to <length_value> and
> the captured value of <name> to conform to <name_value>. Basically I
> want to be able to do more parsing on the captures before succeeding
> on a match. Can I express something like that? I know I can do element
> <- kv -> parse_kv and do furtehr matching inside the parse_kv
> function, but I wanted to avoid fragmenting the parser in multiple
> stages like that.

You can use the '#' operator on a pattern in order to allow to to
match the input against a second pattern.  Here's a really simple
example:

local lpeg = require"lpeg"

local P = lpeg.P
local S = lpeg.S
local R = lpeg.R
local C = lpeg.C

local input1 = "aabbcc"
local input2 = "aabbccd"

local patt1 = S"abc"^2 * P(-1)
local patt2 = R"az"^2 * P(-1)
local test_both = #patt1 * patt2
local test_both_rev = #patt2 * patt1

local function test(input)
	print"*********************"
	print("testing:", input)
	print(patt1:match(input))
	print(patt2:match(input))
	print(test_both:match(input))
	print(test_both_rev:match(input))
	print""
end

test(input1)
test(input2)