Re: Need lpeg hint

[Martin Kortmann <mail@...>]

Am 13.08.2011 um 22:26 schrieb Peter Cawley:

> On Sat, Aug 13, 2011 at 9:09 PM, Martin Kortmann <mail@kortmann.de> wrote:
>> 
>> Am 13.08.2011 um 21:36 schrieb Peter Cawley:
>> 
>>> On Sat, Aug 13, 2011 at 8:18 PM, Martin Kortmann <mail@kortmann.de> wrote:
>>>> Hello all,
>>>> 
>>>> I'm trying to learn the usage of lpeg and i need a push to the right direction on the following problem:
>>>> 
>>>> I will parse files with the following structure:
>>>> 
>>>> blockname1 {
>>>>  key1 value1
>>>>  key2 value2
>>>>  blockname2 {
>>>>    key3 value3
>>>>    blockname3 {
>>>>      key4 value4
>>>>    }
>>>>    key5 value5
>>>>  }
>>>> }
>>>> 
>>>> there are named blocks of datas, the datas are several key/value pairs or other named blocks of datas. Seem simple, but i don't get a right grammar for this syntax.
>>>> Can someone give me a start for this?
>>>> 
>>>> Thanks Martin
>>> 
>>> Very quickly thrown together, but seems to work for your example:
>>> http://codepad.org/z49J4o8z
>>> 
>> 
>> 
>> Thank you Peter, this seems to work. but why does the following code not work?
>> 
>> local L = require "lpeg"
>> 
>> local function makepairs(kvkv_array)
>>  local t = {}
>>  for i = 1, #kvkv_array, 2 do
>>    t[kvkv_array[i]] = kvkv_array[i+1]
>>  end
>>  return t
>> end
>> 
>> local ws = L.S" \r\n\t"^0 -- whitespace
>> local id = L.C(L.R("az","AZ","09")^1) -- identifiers
>> local value = id -- values (currently same as identifiers)
>> 
>> local grammar = L.P { "block",
>> 
>>        entry = ws * id * ws * value + L.V('block'), -- key value OR block
>> 
>>        block = ws * id * ws * "{" * (L.Ct(L.V"entry"^0) / makepairs) * ws * "}" / function(k, v) return {[k] = v} end;
>> 
>> }
>> 
>> local result = grammar:match[[
>> 
>> blockname1 {
>>  key1 value1
>>  key2 value2
>>  blockname2 {
>>   key3 value3
>>   blockname3 {
>>     key4 value4
>>   }
>>   key5 value5
>>  }
>> }
>> 
>> ]]
>> 
>> 
>> Martin
> 
> The "block" non-terminal generates one capture because the function
> merges two captures into one. The "entry" non-terminal generates two
> captures for a key/value pair, but only generates one capture for a
> block. This then confuses makepairs, as it expected every match of the
> "entry" non-terminal to produce two captures.
> 


Hello Peter,

but i can't see the difference between your example and my my code. Maybe there are too many trees in the wood...
Where is the difference between your "pattern" and my "block"?

Martin