[antlr-interest] Positioning input stream (was EOL sequence)
skapp at rochester.rr.com
skapp at rochester.rr.com
Tue Dec 16 21:03:40 PST 2003
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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