Re: ASCII Name and URL Elements (2nd)

[James W. <ja...@fr...>]

Roger Holmes wrote:
> On 14 May, 2007, at 17:23, James W. Walker wrote:
> 
>> On May 14, 2007, at 2:21 AM, Roger Holmes wrote:
>>
>>> On 14 May, 2007, at 00:32, James W. Walker wrote:
>>>
>>>> On May 12, 2007, at 9:10 AM, Stefan Huber wrote:
>>>>
>>>>> Please ignore the previous mail. So once again...
>>>>>
>>>>> "Apple Computer, Inc.:NameElement" and "Apple Computer, Inc.:
>>>>> URLElement" are not very parser friendly.
>>>>>
>>>>> The problem is in E3FFR_3DMF_Text.c/
>>>>> e3fformat_3dmf_text_readobjecttype.
>>>>> E3FileFormat_GenericReadText_ReadUntilChars with argument blank =
>>>>> true cannot read object types with blanks in their name. So the
>>>>> parser tries to handle an object "Apple" and runs into trouble.
>>>> I wish Apple had published a formal grammar for ASCII 3DMF.  It is
>>>> not clear to me how the parser is supposed to know where an object
>>>> type ends, or how to tell the difference between a label and an
>>>> object type.
>>> I agree. But here, can't we just read everything up to the colon?
>> That takes you to the middle of the name element object type.  Then
>> what?
> 
>  From the only two samples so far mentioned, the spaces are only in  
> the first part of the name element object type. The rest is a normal  
> identifier terminated by white space or any non alpha-numeric character.

True... I don't know of any formal rules as to what constitutes a legal 
type name, but it would certainly be an improvement to at least handle 
the standard Apple names.

>> It appears that in a label, the colon should always be
>> followed by a line break.  So, if it's not followed by a line break,
>> we continue reading up to the open parenthesis?
> 
> A parser or any lexical analyser does not need to apply the same  
> rules to a symbol in all circumstances. A label can have different  
> rules to a name element object type. Any compiler can treat a colon  
> in a comment differently from a colon in a statement.

True, but a compiler knows it's looking at a C or C++ comment as soon as 
the comment has started.  A 3DMF parser doesn't know whether it is 
looking at a label or an object type until it has either gone past a 
colon or reached a line break or parenthesis.

-- 
   James W. Walker, Innoventive Software LLC
   <http://www.frameforge3d.com/>