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

[Muhammad Masoom Alam]

Dear All,

If i evaluate the following expression, How the AST
will be created. 
  6 * 4 + 3 + 9

I start the first plus as root and go further:

    *
   / \
  6   +
     / \
    4   +
       / \
      3   9

if i evaluated the tree like this, addition takes
place before the mulitiplication which is not desired.

If any one can help me, how this tree will be
evaluated.

Thanks in advance.
MA


--- Anthony Youngman
<Anthony.Youngman at eca-international.com> wrote:

> 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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