[ragel-users] Default actions that leave the machine

[Murray Henderson]

Hello,

Local and global error actions transition to the error state.

I want DEF to transition to the next machine (ie. behave like a final
state), not the error state.

The parser I am writing is permissive, all input must be accepted (I
never want to goto the error state).

I do not wish to use manual goto recovery, because the parser is large
and complex, such manual tracking is a lot of work and error prone.

Cheers,
Murray



On Tue, Feb 1, 2011 at 4:58 AM, Adrian Thurston
<adrian.thurston at esentire.com> wrote:
> Hi, have you looked at ragel's local and global error actions yet? These may
> do what you want.
>
> -Adrian
>
> On 11-01-26 08:08 PM, Murray Henderson wrote:
>>
>> Hello,
>>
>> I want to embed a default action into a machine that leaves the
>> machine (without using manual a jump inside the action).
>>
>> For simplicities sake, I will call this operator $^^ (since it is
>> similar to the Local Error operator).
>>
>>
>> Example:
>>
>> action parse_error {}
>> helloworld = ('HELLO ' %^^parse_error) 'WORLD';
>>
>> Non-error inputs include:
>> HELLO WORLD
>> HELLOWORLD (parse_error action occurs on 'O' ->  'W' transition)
>> HELLWORLD (parse_error action occurs on 'L' ->  'W' transition)
>> HELWORLD (parse_error action occurs on 'L' ->  'W' transition)
>> HEWORLD (parse_error action occurs on 'E' ->  'W' transition)
>> HWORLD (parse_error action occurs on 'H' ->  'W' transition)
>> WORLD (parse_error action occurs on ->  'W' transition)
>>
>>
>> I can simulate the above behavior with the '?' operator, but that is
>> laborious, and there are other ways of using $^^ that I suspect cannot
>> be simulated.
>>
>>
>> I want this operator because I am trying to make a liberal parser that
>> accepts all possible input. (Every state must have a default action)
>> .I am creating a html5 parser that uses regular machines for
>> tokenizing, and scanners built from the regular machines for parsing.
>> Yes, I am mad.
>>
>> I cannot use manual jumps, because I don't want to jump out of the
>> scanners mid-token.
>>
>>
>> I am willing to try and add this operator into Ragel myself. I have
>> grabbed the source code and tracked my way to fsmap.cpp, where the new
>> operator would be added.
>>
>> Before I continue...
>> Is there already a way to achieve my desired behavior that I am not aware
>> of?
>> Would such an operator be worthwhile? Is it even possible?
>> Is there any knowledge that could be imparted that would help me make a
>> patch?
>>
>> If I do end up making a patch, for symmetry purposes I will make
>> global/local and start/any/final etc versions of the operator.
>>
>> After a brief look through the source, it looks like I would need to
>> mod the FsmAp::fillGaps() function, passing in a (separate object for
>> each?) final state into the FsmAp::attachNewTrans() instead of NULL.
>>
>> Ragel is a wonderful program by the way, thank you for creating it.
>>
>> Cheers,
>> Murray
>>
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>>
>
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