Re: Need lpeg hint
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- Subject: Re: Need lpeg hint
- From: Martin Kortmann <mail@...>
- Date: 2011年8月13日 23:33:49 +0200
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