I am new to Antlr, which I am trying to use to parse simple existing
messages. The message structure is exceptionally simple and
straightforward. Message fields include integer and floating-point
numbers, single letter codes, and field separator characters. Each
individual message type has a narrowly defined structure, needs no look
ahead, and typically has at most 2 possible tokens for any location in
the message.
My problem is that one of the fields is a 2-digit (in ASCII)
representation of a hex number. This is known purely from context. It
seems there should be a simple technique (probably a predicate), to
force this behavior. I just can't seem to find it.
Here is a short sample grammar to illustrate:
grammar sample;
prog : test+ ;
test : 'TEST' COMMA INT COMMA FLOAT ( 'A' | 'B' )
COMMA HEX_DIGIT HEX_DIGIT ;
HEX_DIGIT : '0'..'9' | 'A'..'F' | 'a'..'f' ;
INT : '0'..'9'+ ;
FLOAT : '0'..'9'+ ('.' '0'..'9'*)? ;
COMMA : ',' ;
The associated test input is:
TEST,123,5.6A,2D
TEST,321,4.20A,3B
TEST,45,5.68B,78
For this example, the hex digits are the last 2 characters on each line.
For the first test statement, parsing is successful. For the second, I
get a MismatchedTokenException (0!=0) on the B (the last character).
For the third, I get a MismatchedTokenException(0!=0) on the 7 (the
next to last character). I am definitely confused.
Thanks,
Larry
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