/**
* 解析标识符
*
* @param token
* @return 对应符号表项
* @throws Exception
*/
private SymTabEntry parseIdentifier(Token token) throws Exception {
SymTabEntry id = null;
if (token.getType() == IDENTIFIER) {
String name = token.getText().toLowerCase();
id = symTabStack.lookupLocal(name);
// 申明必须得没有，否则重定义了
if (id == null) {
id = symTabStack.enterLocal(name);
id.setDefinition(definition);
id.appendLineNumber(token.getLineNumber());
} else {
errorHandler.flag(token, IDENTIFIER_REDEFINED, this);
}
token = nextToken();
} else {
errorHandler.flag(token, MISSING_IDENTIFIER, this);
}
return id;
}
/**
* Parse a factor.
*
* @param token the initial token.
* @return the root of the generated parse subtree.
* @throws Exception if an error occurred.
*/
private ICodeNode parseFactor(Token token) throws Exception {
TokenType tokenType = token.getType();
ICodeNode rootNode = null;
switch ((PascalTokenType) tokenType) {
case IDENTIFIER:
{
// Look up the identifier in the symbol table stack.
// Flag the identifier as undefined if it's not found.
String name = token.getText().toLowerCase();
SymTabEntry id = symTabStack.lookup(name);
if (id == null) {
errorHandler.flag(token, IDENTIFIER_UNDEFINED, this);
id = symTabStack.enterLocal(name);
}
rootNode = ICodeFactory.createICodeNode(VARIABLE);
rootNode.setAttribute(ID, id);
id.appendLineNumber(token.getLineNumber());
token = nextToken(); // consume the identifier
break;
}
case INTEGER:
{
// Create an INTEGER_CONSTANT node as the root node.
rootNode = ICodeFactory.createICodeNode(INTEGER_CONSTANT);
rootNode.setAttribute(VALUE, token.getValue());
token = nextToken(); // consume the number
break;
}
case REAL:
{
// Create an REAL_CONSTANT node as the root node.
rootNode = ICodeFactory.createICodeNode(REAL_CONSTANT);
rootNode.setAttribute(VALUE, token.getValue());
token = nextToken(); // consume the number
break;
}
case STRING:
{
String value = (String) token.getValue();
// Create a STRING_CONSTANT node as the root node.
rootNode = ICodeFactory.createICodeNode(STRING_CONSTANT);
rootNode.setAttribute(VALUE, value);
token = nextToken(); // consume the string
break;
}
case NOT:
{
token = nextToken(); // consume the NOT
// Create a NOT node as the root node.
rootNode = ICodeFactory.createICodeNode(ICodeNodeTypeImpl.NOT);
// Parse the factor. The NOT node adopts the
// factor node as its child.
rootNode.addChild(parseFactor(token));
break;
}
case LEFT_PAREN:
{
token = nextToken(); // consume the (
// Parse an expression and make its node the root node.
rootNode = parseExpression(token);
// Look for the matching ) token.
token = currentToken();
if (token.getType() == RIGHT_PAREN) {
token = nextToken(); // consume the )
} else {
errorHandler.flag(token, MISSING_RIGHT_PAREN, this);
}
break;
}
case LEFT_BRACKET:
{
rootNode = parseSet(token);
break;
}
default:
{
errorHandler.flag(token, UNEXPECTED_TOKEN, this);
break;
}
}
return rootNode;
}
/**
* Parse type definitions.
*
* @param token the initial token.
* @throws Exception if an error occurred.
*/
public void parse(Token token) throws Exception {
token = synchronize(IDENTIFIER_SET);
// Loop to parse a sequence of type definitions
// separated by semicolons.
while (token.getType() == IDENTIFIER) {
String name = token.getText().toLowerCase();
SymTabEntry typeId = symTabStack.lookupLocal(name);
// Enter the new identifier into the symbol table
// but don't set how it's defined yet.
if (typeId == null) {
typeId = symTabStack.enterLocal(name);
typeId.appendLineNumber(token.getLineNumber());
} else {
errorHandler.flag(token, IDENTIFIER_REDEFINED, this);
typeId = null;
}
token = nextToken(); // consume the identifier token
// Synchronize on the = token.
token = synchronize(EQUALS_SET);
if (token.getType() == EQUALS) {
token = nextToken(); // consume the =
} else {
errorHandler.flag(token, MISSING_EQUALS, this);
}
// Parse the type specification.
TypeSpecificationParser typeSpecificationParser = new TypeSpecificationParser(this);
TypeSpec type = typeSpecificationParser.parse(token);
// Set identifier to be a type and set its type specificationt.
if (typeId != null) {
typeId.setDefinition(TYPE);
}
// Cross-link the type identifier and the type specification.
if (type != null && typeId != null) {
if (type.getIdentifier() == null) {
type.setIdentifier(typeId);
}
typeId.setTypeSpec(type);
} else {
token = synchronize(FOLLOW_SET);
}
token = currentToken();
TokenType tokenType = token.getType();
// Look for one or more semicolons after a definition.
if (tokenType == SEMICOLON) {
while (token.getType() == SEMICOLON) {
token = nextToken(); // consume the ;
}
}
// If at the start of the next definition or declaration,
// then missing a semicolon.
else if (NEXT_START_SET.contains(tokenType)) {
errorHandler.flag(token, MISSING_SEMICOLON, this);
}
token = synchronize(IDENTIFIER_SET);
}
}