[antlr-interest] Re: Perority Enforcing using Antlr Grammar

[Anthony Youngman]

To expand this ...

Firstly there should be plenty of examples in various grammars but basically the idea is to bind the highest priority stuff first, then the lower stuff. Using standard mathematical priorities...

highestexpr: ID ( ( "*" | "/" ) ID )*;
midexpr: highestexpr ( ( "+" | "-" ) highestexpr );*
expr: midexpr ( ( "AND" | "OR" ) midexpr );*

To explain what it's doing, "highestexpr" grabs all your variable names, and binds them to the highest operators (here arithmetical multiply and divide). "midexpr" then comes along and binds all the "highestexpr"s to the add and subtract. Finally "expr" comes along and binds all the "midexpr" to your lowest operators, "AND" and "OR". Just add more levels for more levels of priority.

As an example, let's take

6 * 4 AND 3 + 9
ID * ID AND ID + ID
highestexpr AND highestexpr + highestexpr
midexpr AND midexpr
expr

Cheers,
Wol

-----Original Message-----
From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-bounces at antlr.org] On Behalf Of Koehne Kai
Sent: 16 June 2006 09:33
To: antlr-interest at antlr.org
Subject: [antlr-interest] Re: Perority Enforcing using Antlr Grammar

Hi,
 
try something like
 
expr1: expr2 ("OR" expr2)*;
expr2: expr3 ("AND" expr3)*;
expr3: ID | "(" expr1 ")";
 
Regards,
 
Kai Koehne

 
________________________________

Von: antlr-interest-bounces at antlr.org im Auftrag von Muhammad Masoom Alam
Gesendet: Fr 16.06.2006 08:42
An: antlr-interest at antlr.org
Betreff: [antlr-interest] Perority Enforcing using Antlr Grammar



Hi all,

 sorry if my question is a stupid one, as i am a new
bie. How to enforce perority rules using Antlr.

e.g. I have the following conditions

  (Predicate1 And (Predicate2 Or Predicate3))

In the above, Grammar, paranthesis are used to group
and enforce perority, but how this will be done using
the Antlr Grammar.

Thanks in Advance.
MA

Muhammad Masoom Alam
Security Engineering Universität Innsbruck
Institut für Informatik Technikerstraße 13  A - 6020 Innsbruck
Tel.: ++43 - 512 - 507 6462
http://qe-informatik.uibk.ac.at/


               
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