[furcas-discussion] Parser Invariants

[Thomas Goldschmidt]

Hi Stephan,

         * Is it guaranteed that the parser does not change the textual
        representation? (Seems like a obvious yes to me, but I'd like to
        have your confirmation on this)
That depends on what you conceive the "textual representation". If you 
mean the text that a user sees in the editor the answer is yes. Of course, 
the structure of the textblocks model is altered which, however, won't 
change what the user sees.
      * The lexer takes the PREVIOUS version and creates the CURRENT
        one. If there is an existing CURRENT version, it is discarded
        first. 
        - What does the parser do with these two versions?
The parser uses the versions (in fact also the REFERENCE version) do 
determine where the places in the textblocks model that were newly 
created, modified or deleted.
        - When the parser has finished, are both versions consistent views 
on model
        or are they somewhat different?
They are different, as the PREVIOUS version will still contain tokens that 
just contain modified values an that are not lexecally analysed. E.g., 
after an insertion " bla" to the Token "test" resulting in PREVIOUS 
version token "test bla" this value is still present in the PREVIOUS 
version token whereas the CURRENT version may have (of course depending on 
the lexer rules) two tokens "test" "bla". Therefore, after the CURRENT 
version is reached the PREVIOUS version is obsolete as it is missing the 
tokenisation that the lexer did.
      * Is the latest CURRENT version promoted to become the new
        PREVIOUS version?
No, after the CURRENT version is finished by the parser (currently after 
performing a save action), the CURRENT version becomes the new REFERENCE 
version. Only after a user again makes modifications to the document, a 
new PREVIOUS version will be created.
      * Is it dangerous to set errorMode=True in the parse run and force
        the parser to inject as far as possible, even if there are
        syntax errors?
This was my first try to achieve a backgound parsing. However, there were 
still some problems with subsequent editings where the intermediate 
version was still erronous. To answer your question, yes it is dangerous. 
I cant remember what exactly the problems where when I trie to do this. Is 
that what you are currently working on? to get the background parsing to 
create as much of the model as possible? That would be great ;) I will try 
to help you as much as my available time lets me do this.

Cheers,
Thomas


 
Thomas Goldschmidt 

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Stephan Erb <stephan at dev.static-void.de> 
Sent by: furcas-discussion-bounces at lists.furcas.org
16.02.2011 00:12

To
furcas-discussion <furcas-discussion at lists.furcas.org>
cc

Subject
[furcas-discussion] Parser Invariants






Hey Thomas,

I have a few simple questions concerning incremental lexing and parsing.

      * Is it guaranteed that the parser does not change the textual
        representation? (Seems like a obvious yes to me, but I'd like to
        have your confirmation on this)
      * The lexer takes the PREVIOUS version and creates the CURRENT
        one. If there is an existing CURRENT version, it is discarded
        first. What does the parser do with these two versions? When the
        parser has finished, are both versions consistent views on model
        or are they somewhat different?
      * Is the latest CURRENT version promoted to become the new
        PREVIOUS version?
      * Is it dangerous to set errorMode=True in the parse run and force
        the parser to inject as far as possible, even if there are
        syntax errors?

I ask all these questions because they are crucial when determining the
critical regions for the synchronization of the background parsing
thread. 

Thanks!
Stephan

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