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package com.craftinginterpreters.lox;
import static com.craftinginterpreters.lox.TokenType.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Arrays;
class Parser {
private static class ParseError extends RuntimeException {
}
private final List<Token> tokens;
private int current = 0;
Parser(List<Token> tokens) {
this.tokens = tokens;
}
public List<Stmt> parse() {
List<Stmt> statements = new ArrayList<>();
while (!isAtEnd()) {
statements.add(declaration());
}
return statements;
}
private Expr expression() {
return assignment();
}
private Stmt declaration() {
try {
if (match(VAR))
return varDeclaration();
return statement();
} catch (ParseError error) {
synchronize();
return null;
}
}
private Stmt statement() {
if (match(FOR))
return forStatement();
if (match(IF))
return ifStatement();
if (match(PRINT))
return printStatement();
if (match(WHILE))
return whileStatement();
if (match(LEFT_BRACE))
return new Stmt.Block(block());
return expressionStatement();
}
private Stmt forStatement() {
consume(LEFT_PAREN, "Expect '(' after 'for'.");
Stmt initializer;
if (match(SEMICOLON)) {
initializer = null;
} else if (match(VAR)) {
initializer = varDeclaration();
} else {
initializer = expressionStatement();
}
Expr condition = null;
if (!check(SEMICOLON)) {
condition = expression();
}
consume(SEMICOLON, "Expect ';' after loop condition.");
Expr increment = null;
if (!check(RIGHT_PAREN)) {
increment = expression();
}
consume(RIGHT_PAREN, "Expect ')' after for clauses.");
Stmt body = statement();
if (increment != null) {
body = new Stmt.Block(
Arrays.asList(
body,
new Stmt.Expression(increment)));
}
if (condition == null) condition = new Expr.Literal(true);
body = new Stmt.While(condition, body);
if (initializer != null) {
body = new Stmt.Block(Arrays.asList(initializer, body));
}
return body;
}
private Stmt ifStatement() {
consume(LEFT_PAREN, "Expect '(' after 'if'.");
Expr condition = expression();
consume(RIGHT_PAREN, "Expect ')' after if condition.");
Stmt thenBranch = statement();
Stmt elseBranch = null;
if (match(ELSE)) {
elseBranch = statement();
}
return new Stmt.If(condition, thenBranch, elseBranch);
}
private Stmt printStatement() {
Expr value = expression();
consume(SEMICOLON, "Expect ';' after value.");
return new Stmt.Print(value);
}
private Stmt varDeclaration() {
Token name = consume(IDENTIFIER, "Expect variable name.");
Expr initializer = null;
if (match(EQUAL)) {
initializer = expression();
}
consume(SEMICOLON, "Expect ';' after variable declaration.");
return new Stmt.Var(name, initializer);
}
private Stmt whileStatement() {
consume(LEFT_PAREN, "Expect '(' after 'while'.");
Expr condition = expression();
consume(RIGHT_PAREN, "Expect ')' after condition.");
Stmt body = statement();
return new Stmt.While(condition, body);
}
private Stmt expressionStatement() {
Expr expr = expression();
consume(SEMICOLON, "Expect ';' after expression.");
return new Stmt.Expression(expr);
}
private List<Stmt> block() {
List<Stmt> statements = new ArrayList<>();
while (!check(RIGHT_BRACE) && !isAtEnd()) {
statements.add(declaration());
}
consume(RIGHT_BRACE, "Expect '}' after block.");
return statements;
}
private Expr assignment() {
Expr expr = or();
if (match(EQUAL)) {
Token equals = previous();
Expr value = assignment();
if (expr instanceof Expr.Variable) {
Token name = ((Expr.Variable) expr).name;
return new Expr.Assign(name, value);
}
error(equals, "Invalid assignment target.");
}
return expr;
}
private Expr or() {
Expr expr = and();
while (match(OR)) {
Token operator = previous();
Expr right = and();
expr = new Expr.Logical(expr, operator, right);
}
return expr;
}
private Expr and() {
Expr expr = equality();
while (match(AND)) {
Token operator = previous();
Expr right = equality();
expr = new Expr.Logical(expr, operator, right);
}
return expr;
}
private Expr equality() {
Expr expr = comparison();
while (match(BANG_EQUAL, EQUAL_EQUAL)) {
Token operator = previous();
Expr right = comparison();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr comparison() {
Expr expr = term();
while (match(GREATER, GREATER_EQUAL, LESS, LESS_EQUAL)) {
Token operator = previous();
Expr right = term();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr term() {
Expr expr = factor();
while (match(MINUS, PLUS)) {
Token operator = previous();
Expr right = factor();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr factor() {
Expr expr = unary();
while (match(SLASH, STAR)) {
Token operator = previous();
Expr right = unary();
expr = new Expr.Binary(expr, operator, right);
}
return expr;
}
private Expr unary() {
if (match(BANG, MINUS)) {
Token operator = previous();
Expr right = unary();
return new Expr.Unary(operator, right);
}
return primary();
}
private Expr primary() {
if (match(FALSE))
return new Expr.Literal(false);
if (match(TRUE))
return new Expr.Literal(true);
if (match(NIL))
return new Expr.Literal(null);
if (match(NUMBER, STRING)) {
return new Expr.Literal(previous().literal);
}
if (match(IDENTIFIER)) {
return new Expr.Variable(previous());
}
if (match(LEFT_PAREN)) {
Expr expr = expression();
consume(RIGHT_PAREN, "Expect ')' after expression.");
return new Expr.Grouping(expr);
}
throw error(peek(), "Expect expression.");
}
private boolean match(TokenType... types) {
for (TokenType type : types) {
if (check(type)) {
advance();
return true;
}
}
return false;
}
private Token consume(TokenType type, String message) {
if (check(type))
return advance();
throw error(peek(), message);
}
private boolean check(TokenType type) {
if (isAtEnd())
return false;
return peek().type == type;
}
private Token advance() {
if (!isAtEnd())
current++;
return previous();
}
private boolean isAtEnd() {
return peek().type == EOF;
}
private Token peek() {
return tokens.get(current);
}
private Token previous() {
return tokens.get(current - 1);
}
private ParseError error(Token token, String message) {
Lox.error(token, message);
return new ParseError();
}
private void synchronize() {
advance();
while (!isAtEnd()) {
if (previous().type == SEMICOLON)
return;
switch (peek().type) {
case CLASS:
case FUN:
case VAR:
case FOR:
case IF:
case WHILE:
case PRINT:
case RETURN:
return;
}
advance();
}
}
}
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