/**
* Parse an expression
*
* @param token the initial token.
* @return the root of the generated parse subtree.
* @throws Exception if an error occurred.
*/
private ICodeNode parseExpression(Token token) throws Exception {
// Parse a simple expression and make the root of its tree
// the root node.
ICodeNode rootNode = parseSimpleExpression(token);
TypeSpec resultType = rootNode != null ? rootNode.getTypeSpec() : Predefined.undefinedType;
token = currentToken();
TokenType tokenType = token.getType();
// Look for a relational operator.
if (REL_OPS.contains(tokenType)) {
// Create a new operator node and adopt the current tree as its first child
ICodeNodeType nodeType = REL_OPS_MAP.get(tokenType);
ICodeNode opNode = ICodeFactory.createICodeNode(nodeType);
opNode.addChild(rootNode);
token = nextToken(); // consume the operator
// Parse the second simple expression.
// The operator node adopts the simple expression's tree as its second child.
ICodeNode simExprNode = parseSimpleExpression(token);
opNode.addChild(simExprNode);
// The operator node becomes the new root node.
rootNode = opNode;
// Type check: The operands must be comparison compatible.
TypeSpec simExprType =
simExprNode != null ? simExprNode.getTypeSpec() : Predefined.undefinedType;
if (TypeChecker.areComparisionCompatible(resultType, simExprType))
resultType = Predefined.booleanType;
else {
errorHandler.flag(token, INCOMPATIBLE_TYPES, this);
resultType = Predefined.undefinedType;
}
}
if (rootNode != null) rootNode.setTypeSpec(resultType);
return rootNode;
}
