So you basically have two types of expressions, those that start with INT
'/' and those that don't. So this would look like:
time_expr
: INT '/' time_ltr
| time_rtl
;
time_rtl
: (INT ':' (INT ':')?)? INT '.' INT;
time_ltr
: INT (':' INT (':' INT ('.' INT)?)?)?
;
Is this what you tried and it failed?
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Rick Mann
Sent: Saturday, April 24, 2010 6:07 AM
To: antlr-interest Interest
Subject: [antlr-interest] Parsing a time expression
I posted a couple related questions earlier, but now I'm down to a more
fundamental question.
I'm trying to use a complete lexer/parser/tree parser. I'd like to support
two types of expressions representing time intervals. In the end, they
evaluate to a value representing seconds. The two types look like this:
1) 15/
2) 15/ 23
3) 15/ 23:12
4) 15/ 23:12:07
5) 15/ 23:12:07.2
and
6) 7.2
7) 12:07.2
8) 23:12:07.2
The main difference is that if the expression starts with INT '/', then it's
built up left-to-right with each value representing days, hours, minutes,
and seconds, respectively. If there is no '/' in the expression, it's built
up right-to-left, with seconds in the right-most position.
I'm having trouble conceptualizing what the grammar really should look like,
and how the tree parser would look. When I try to write stuff out in the
form of INT '/'! (INT (':'! INT)?)?, I get lots of "matches more than one
alternative" warnings.
OTOH, one can think of these as arithmetic expressions. Considering example
5 above, it would be:
24 * 3600 * 15
+ 3600 * 23
+ 60 * 12
+ 7.2
------------------
1379527.2
But I can't figure out how to build the tree that accounts for the position
of each element to allow all the alternatives 1 - 5.
Thanks for any guidance.
--
Rick
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