[antlr-interest] Re: Change operator precedence in a AST

[Pete Forman]

At 2004-09-27 08:04 +0000, lgcraymer wrote:
>You still can use the AST to generate code--just insert parentheses in
>the appropriate spots.

Here's a code extract showing a set of rules applied and part of the
tree processing code implementing those rules.

//             _____ ___________ _______
//____operator U+ U-  *   /   %   +   -   <>  =!
//____operand        L R L R L R L R L R L R L R
//     unary+   .  . . . . . . . . . . . . . . .
//___  unary-   .  . . . . . . . . . . . . . . .
//         *    O  O . . . O . O . . . . . . . .
//         /    O  O . O . O . O . . . . . . . .
//___      %    O  O . O . O . O . . . . . . . .
//         +    O  O O O O O O O . . . O . . . .
//___      -    O  O O O O O O O . . . O . . . .
//___     <>    O  O O O O O O O O O O O . O . .
//        =!    O  O O O O O O O O O O O O O . O
//     primit   .  . . . . . . . . . . . . . . .

//  O means that the operand should be parenthesized
//  . means that the operand should be printed as is
// =! stands for = or !=
// <> stands for < or > or <= or >=

additive_expression returns [String s]
{ s = "";
   StringBuffer buf = new StringBuffer();
   String s1, s2;
}
   : #(PLUS s1=e1:subexpression s2=e2:subexpression)
     { switch (e1.getType()) {
       case LESS_THAN:
       case LESS_THAN_OR_EQUAL:
       case GREATER_THAN:
       case GREATER_THAN_OR_EQUAL:
       case EQUAL:
       case NOT_EQUAL:
       case AND:
       case OR:
         buf.append("(").append(s1).append(") + ");
         break;
       default:
         buf.append(s1).append(" + ");
       }
       switch (e2.getType()) {
       case LESS_THAN:
       case LESS_THAN_OR_EQUAL:
       case GREATER_THAN:
       case GREATER_THAN_OR_EQUAL:
       case EQUAL:
       case NOT_EQUAL:
       case AND:
       case OR:
         buf.append("(").append(s2).append(")");
         break;
       default:
         buf.append(s2);
       }
       s = buf.toString();
     }
   ;


-- 
Pete Forman                -./\.-  Disclaimer: This post is originated
WesternGeco                  -./\.-   by myself and does not represent
pete.forman at westerngeco.com    -./\.-   opinion of Schlumberger, Baker
http://petef.port5.com           -./\.-   Hughes or their divisions.



 
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