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package Interpreter;
import java.util.ArrayList;
import java.util.List;
public class Parser {
private final List<Token> tokens;
private int currentToken = 0;
Parser(List<Token> tokens){
this.tokens=tokens;
}
List<Statement> parse(){
List<Statement> statements = new ArrayList<>();
while (!checkEOF()){
statements.add(declaration());
}
return statements;
}
private Statement declaration(){
try{
if (matchAndAdvance(TokenType.VAR)){
if (matchOrError(TokenType.DEFINE, ":: Required for variable definition")){
if (matchOrError(TokenType.IDENTIFIER,"Expected variable name.")){
Token varName = getPreviousToken();
return new Statement.VariableDeclaration(varName);
}
}
}
return statement();
} catch (Error e){
currentToken++;
return null;
}
}
private Statement statement(){
if (matchAndAdvance(TokenType.PRINT)){
Expression expression = expression();
return new Statement.PrintStatement(expression);
}
return expressionStatement();
}
private Statement expressionStatement(){
Expression expression = assignment();
return new Statement.ExpressionStatement(expression);
}
private Expression assignment(){
Expression variable = expression();
if (matchAndAdvance(TokenType.EQUALS)){
Expression assignedvalue = expression();
if (variable instanceof Expression.Variable){
return new Expression.AssignmentExpression(((Expression.Variable)variable).name,assignedvalue);
}
throw error("Incorrect assignment operation");
}
return variable;
}
private Expression expression(){
Expression createdExpression = equality();
return createdExpression;
}
private Expression equality(){
Expression createdExpression = comparison();
while (matchAndAdvance(TokenType.EQUALITY)){
Token op = getPreviousToken();
Expression right = comparison();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression comparison(){
Expression createdExpression = term();
while (matchAndAdvance(TokenType.GREATER)||matchAndAdvance(TokenType.LESS)){
Token op = getPreviousToken();
Expression right = term();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression term(){
Expression createdExpression = factor();
while (matchAndAdvance(TokenType.PLUS)||matchAndAdvance(TokenType.MINUS)){
Token op = getPreviousToken();
Expression right = factor();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression factor(){
Expression createdExpression = primary();
while (matchAndAdvance(TokenType.STAR)||matchAndAdvance(TokenType.SLASH)){
Token op = getPreviousToken();
Expression right = primary();
createdExpression = new Expression.Binary(createdExpression, op, right);
}
return createdExpression;
}
private Expression primary(){
if (matchAndAdvance(TokenType.NUMBER)){
return new Expression.Literal(getPreviousToken());
}
if (matchAndAdvance(TokenType.IDENTIFIER)) {
return new Expression.Variable(getPreviousToken());
}
if (matchAndAdvance(TokenType.LEFT_PAREN)){
Expression expr = expression();
if (matchAndAdvance(TokenType.RIGHT_PAREN)){
return new Expression.BracketedExpression(expr);
}
else{
throw error("Expected ')");
}
}
throw error("Expected Expression");
}
private void advanceToken(){
if (!checkEOF()) {
currentToken++;
};
}
private boolean matchAndAdvance(TokenType type){
if (checkToken(type)) {
advanceToken();
return true;
}
return false;
}
private boolean matchOrError(TokenType type,String errorMessage){
if (matchAndAdvance(type)){
return true;
}
throw error(errorMessage);
}
private boolean checkToken(TokenType type){
if (checkEOF()) return false;
return getCurrentToken().type == type;
}
private boolean checkEOF(){
return tokens.get(currentToken).type==TokenType.EOF;
}
private Token getCurrentToken(){
return tokens.get(currentToken);
}
private Token getPreviousToken(){
return tokens.get(currentToken - 1);
}
private Error error(String message){
Language.displayError(message);
return new Error();
}
}
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