From murdoch at stats.uwo.ca  Fri Jun 19 05:40:30 2009
From: murdoch at stats.uwo.ca (Duncan Murdoch)
Date: Fri, 19 Jun 2009 05:40:30 +0200
Subject: [Rd] R_parseVector and syntax error [was: error messages while
 parsing with rniParse]
In-Reply-To: <EFC2C284-8863-4E5E-85CF-4AB223238302@r-project.org>
References: <4A36715A.2020003@dbmail.com>	<63D1BDD5-D697-4F84-96A8-CD89AE8C4113@r-project.org>
	<4A3A8141.6080401@dbmail.com> <4A3AAB4D.8030100@stats.uwo.ca>
	<EFC2C284-8863-4E5E-85CF-4AB223238302@r-project.org>
Message-ID: <4A3B08AE.5080405@stats.uwo.ca>

Simon Urbanek wrote:
> On Jun 18, 2009, at 17:02 , Duncan Murdoch wrote:
>
>   
>> Romain Francois wrote:
>>     
>>> Hello,
>>>
>>> [I'm redirecting this here from stats-rosuda-devel]
>>>
>>> When parsing R code through R_parseVector and the code generates an  
>>> error (syntax error), is there a way to grab the error.
>>> It looks like yyerror populates the buffer "R_ParseErrorMsg", but  
>>> then the variable is not part of the public api.
>>>
>>> Would it be possible to add yet another entry point to the parser  
>>> that would basically wrap R_parseVector so that it would have an  
>>> extra char* argument that would bring back the error message if  
>>> there is an error?
>>>
>>>
>>>       
>> I would oppose that.  Suggest ways to reduce the complexity of the  
>> parser interface and I'd be interested.  It's a nightmare to make  
>> any changes there.
>>
>> You can always call the R function wrapped in try(), so it's not as  
>> though this would give you anything that you don't already have  
>> access to.
>>     
>
>
> I'm not quite following - we're talking about R_ParseVector in C code  
> so the point is that the C code gets access to the error message so it  
> can relay it to the user. 

I understood that.  But the C code can get the error message by 
evaluating an R expression and looking at the result.

> There are no R-level functions involved  
> here. The issue here for the moment is that this information is  
> retrievable at R level but not (officially) at the C level. 

I wouldn't mind exposing the underlying information in a clean way, but 
the string in R_ParseVector isn't all a front end should get. 

At the time of an R_ParseVector syntax error, the parser knows what 
token it couldn't handle, and it knows its classification, and the 
location in the file where it came from.   Not all of that makes it 
through to the error message. 

> As for  
> reducing complexity - technically, there is no complexity added since  
> all this is already in place ... [adding extra char * argument to  
> ParseVector may not be the best way but that's not what I'm arguing  
> for]. 
>   

It was what I was arguing against.

Duncan Murdoch

> Or am I missing something?

> Cheers,
> S
>
>
>   
>>> Romain
>>>
>>> Simon Urbanek wrote:
>>>
>>>       
>>>> On Jun 15, 2009, at 12:05 , Romain Francois wrote:
>>>>
>>>>
>>>>         
>>>>> Hello,
>>>>>
>>>>> In JRI, is there a way to get the error message that is generated  
>>>>> by the
>>>>> parser through rniParse
>>>>> For example, if I have this :
>>>>>
>>>>> long y = re.rniParse( "rnorm( 10 ))", 1 ) ;
>>>>>
>>>>> this obviously generates a parse error, so y will be the same as
>>>>> (R_NilValue) :
>>>>>
>>>>> long null_id = re.rniEval( re.rniParse( "NULL", 1 ), 0 ) ;
>>>>>
>>>>> I guess the underlying question is : "Is R_ParseErrorMsg exposed to
>>>>> JRI".
>>>>>
>>>>>           
>>>> AFAICT R_ParseErrorMsg and friends are not exposed by the R API -  
>>>> they are not accessible outside, so they cannot be use by JRI. It  
>>>> would be nice if there was a way of accessing that info, but R  
>>>> doesn't currently support that.
>>>>
>>>> Cheers,
>>>> Simon
>>>>
>>>>
>>>>         
>>>>> The reason is I would like to bring back the message as part of an
>>>>> exception generated when the code does not parse.
>>>>>
>>>>> Romain
>>>>>
>>>>>           
>>>
>>>       
>> ______________________________________________
>> R-devel at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-devel
>>
>>
>>



[Rd] R_parseVector and syntax error [was: error messages while parsing with rniParse]
Duncan Murdoch