Re: Help with an LPEG Grammar

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

Great! It really helped, thanks!

I have never used this table capture..

:-)
Luís Eduardo Jason Santos



On Fri, Jun 19, 2009 at 6:10 PM, Peter Cawley<lua@corsix.org> wrote:
> Perhaps something like the following?
>
> local input = [[
>     %[ one
>     %[ two ]%
>     %[ three
>             %[ four ]%
>          five ]%
>      six ]%
> ]]
>
> local lpeg = require "lpeg"
> local C, Ct, P, R, S, V = lpeg.C, lpeg.Ct, lpeg.P, lpeg.R, lpeg.S, lpeg.V
>
> local grammar = P { "entity";
>  whitespace = S" \t\r\n"^0,
>  open = P"%[",
>  close = P"]%",
>  name = C(R("az", "AZ", "__")^1),
>  item = (V"name" + V"entity") * V"whitespace",
>  entity = V"whitespace" * Ct(V"open" * V"whitespace" * V"item"^0 * V"close"),
> }
>
> local t = grammar:match(input)
>
> local function print_a(t)
>  io.write"{"
>  for i, v in ipairs(t) do
>    if type(v) == "table" then
>      print_a(v)
>    else
>      io.write(("%q"):format(v))
>    end
>    if t[i + 1] then
>      io.write", "
>    end
>  end
>  io.write"}"
> end
>
> print_a(t) --> {"one", {"two"}, {"three", {"four"}, "five"}, "six"}
>
>
> 2009/6/19 Luís Eduardo Jason Santos <jasonsantos@gmail.com>:
>> 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
>>
>>
>