[ragel-users] Parsing a template language

[Tobias Lütke]

Depends on the answers in this thread I suppose :-)



On Tue, Jul 27, 2010 at 3:42 AM, Magnus Holm <judofyr at gmail.com> wrote:
> (A little off-topic, but whatever:
>
> So Liquid will finally get a proper parser? :-))
>
> // Magnus Holm
>
>
>
> On Tue, Jul 27, 2010 at 03:15, Tobias Lütke <tobi at leetsoft.com> wrote:
>> I've been working on a parser for simple template language. I'm using Ragel.
>>
>> The requirements are modest. I'm trying to find [[tags]] that can be
>> embedded anywhere in the input string.
>>
>> I'm trying to parse a simple template language, something that can
>> have tags such as {{foo}} embedded within HTML. I tried several
>> approaches to parse this but had to resort to using a Ragel scanner
>> and use the inefficient approach of only matching a single character
>> as a "catch all". I feel this is the wrong way to go about this. I'm
>> essentially abusing the longest-match bias of the scanner to implement
>> my default rule ( it can only be 1 char long, so it should always be
>> the last resort ).
>>
>> %%{
>>
>>  machine parser;
>>
>>  action start      { tokstart = p; }
>>  action on_tag      { results << [:tag, data[tokstart..p]] }
>>  action on_static  { results << [:static, data[p..p]] }
>>
>>  tag  = ('[[' lower+ ']]') >start @on_tag;
>>
>>  main := |*
>>    tag;
>>    any      => on_static;
>>  *|;
>>
>> }%%
>>
>> ( actions written in ruby, but should be easy to understand ).
>>
>> How would you go about writing a parser for such a simple language? Is
>> Ragel maybe not the right tool? It seems you have to fight Ragel tooth
>> and nails if the syntax is unpredictable such as this.
>>
>>
>> Regards
>> -- tobi
>>
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>>
>
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