[antlr-interest] Re: Positioning input stream (was EOL sequence)

lgc at mail1.jpl.nasa.gov lgc at mail1.jpl.nasa.gov
Wed Dec 17 15:41:12 PST 2003


I had a thought.  Have you set k to 2 or higher in your lexer?  If it's 1, that would cause problems.


--- In antlr-interest at yahoogroups.com, skapp at r... wrote:
> I have worked out enough details with the EOL sequences to 
> understand where my PostScript parser is failing. PostScript parsers 
> have to be able to handle the following four example sequences 
> identically:
> currentfile read 3
> currentfile read<CR>3
> currentfile read<LF>3
> currentfile read<CR><LF>3
> where the "currentfile read" operator sequence instructs the 
> PostScript interpreter to read one byte from the input stream.
> There is no issue with the first three examples. The input stream 
> point just past the EOL byte once the "read" operator has been 
> recognized. Then the read operator simply has to pull one byte from 
> the input stream (a FileInputStream in this case).
> However, in the fourth case, the input stream points to the <LF> 
> character when the "read" operator has been recognized. The 
> PostScript spec states that "Any of the three forms of EOL ... is 
> treated as a single white-space character."
> How do I handle this? What can or should I do in the lexer versus in 
> the parser?
> Regards,
>    Steve


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