[antlr-interest] Positioning input stream (was EOL sequence)
Albert Huh
albert.huh at embarcadero.com
Wed Dec 17 09:08:32 PST 2003
i don't know too much about ps syntax, but you could simply make your whitespace rule consume spaces as well as newlines in your lexer. the java example that comes with antlr does this.
-----Original Message-----
From: skapp at rochester.rr.com [mailto:skapp at rochester.rr.com]
Sent: Wednesday, December 17, 2003 12:04 AM
To: antlr-interest at yahoogroups.com
Subject: [antlr-interest] Positioning input stream (was EOL sequence)
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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