Help with an LPEG Grammar

[Luís Eduardo Jason Santos <jasonsantos@...>]

Hi,

I know this is probably a trivial problem for you, people, but I was hoping you could provide me some advice regarding this problem I am facing while building an LPEG Grammar.

I am trying to create a parser that reads a recursive pattern and builds a tree with each capture.

Given the example:

 s = [[
     %[ one
     %[ two ]%
     %[ three 
             %[ four ]%
          five ]%
      six ]%

]]

I would like to get a response 't' where

 t = { "one", {"two"}, {"three", {"four"}, "five"}, "six" }


I have written a simple grammar to experiment with the problem, but I couldn't think of a way to solve it.


require'luarocks.require'
require'lpeg'

local SPACE    = lpeg.S" \t\n\f"
local OPEN    = lpeg.P"%["
local CLOSE    = lpeg.P"]%"
local ITEM, SIMPLEITEM, NONITEM, CONTENT = lpeg.V'ITEM', lpeg.V'SIMPLEITEM', lpeg.V'NONITEM', lpeg.V'CONTENT'

local item = function(content)
    print('>', content)
    -- TODO: ??
end

local simpleitem = function(content)
    print('>', content)
    -- TODO: ??
end

local PATT = {
    CONTENT,
    ITEM    = OPEN * lpeg.C(CONTENT) * CLOSE,
    SIMPLEITEM = OPEN * lpeg.C(NONITEM^0) * CLOSE,
    NONITEM = 1-(OPEN + CLOSE),
    CONTENT = (SPACE + SIMPLEITEM / simpleitem + ITEM / item + NONITEM)^1 
}

lpeg.match(PATT, s)


 I wonder if the answer is at some feature of LPEG that I am not quite familiar with yet (like folding captures). I have tried that one, but It didn't seemed quite right for the job (since I would probablly have to add some constant captures and make a 'switch' inside the function to infer my position on the grammar).

Can anyone throw me a bone?

Att.
Luís Eduardo Jason Santos