com.sonar.sslr.impl.ast

Class LeftAssociative

java.lang.Object

com.sonar.sslr.impl.ast.LeftAssociative

Deprecated.

in 1.15

@Deprecated
public final class LeftAssociative
extends java.lang.Object

Utility class which helps to deal with left associative rules, which typically have the form:

 higherPrecendenceExpressionRule.is(
     lowerPrecedenceExpressionRule,
     o2n(highPrecedenceOperator, lowerPrecedenceExpressionRule)
     ).skipIfOneChild();
 

Let's take as an example a simple calculator with the binary subtraction as only operator:

 primaryExpression.is(INTEGER_LITERAL);

 substractionExpression.is(
     primaryExpression,
     o2n("-", primaryExpression)
     ).skipIfOneChild();
 

The interpretation of the subtraction is made easy by this class, and is done as follows:

 public int evaluate(AstNode node) {
   if (node.getType() == primaryExpression) {
     return evaluatePrimaryExpression(node);
   } else if (node.getType() == substractionExpression) {
     return evaluateSubtractionExpression(node);
   } else {
     throw new IllegalArgumentException("Unsupported node type " + node.getType());
   }
 }

 private int evaluatePrimaryExpression(AstNode node) {
   return Integer.parseInt(node.getTokenOriginalValue());
 }

 private int evaluateSubtractionExpression(AstNode node) {
   int accumulator = evaluate(node.getChild(0));

   for (LeftAssociative.OperatorAndOperand operatorAndOperand : new LeftAssociative.Iterator(node)) {
     // If several binary operators have the same precedence, use operatorAndOperand.getOperator()
     accumulator -= evaluate(operatorAndOperand.getOperand());
   }

   return accumulator;
 }
 

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	LeftAssociative.Iterator Deprecated.
static class	LeftAssociative.OperatorAndOperand Deprecated.

Method Summary

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait