Control flow chapter
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@ -27,6 +27,11 @@ public class AstPrinter implements Expr.Visitor<String> {
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return expr.value.toString();
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}
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@Override
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public String visitLogicalExpr(Expr.Logical expr) {
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return parethesize(expr.operator.lexeme, expr.left, expr.right);
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}
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@Override
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public String visitUnaryExpr(Expr.Unary expr) {
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return parethesize(expr.operator.lexeme, expr.right);
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@ -8,6 +8,7 @@ abstract class Expr {
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R visitBinaryExpr(Binary expr);
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R visitGroupingExpr(Grouping expr);
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R visitLiteralExpr(Literal expr);
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R visitLogicalExpr(Logical expr);
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R visitUnaryExpr(Unary expr);
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R visitVariableExpr(Variable expr);
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}
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@ -65,6 +66,22 @@ abstract class Expr {
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final Object value;
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}
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static class Logical extends Expr {
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Logical(Expr left, Token operator, Expr right) {
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this.left = left;
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this.operator = operator;
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this.right = right;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitLogicalExpr(this);
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}
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final Expr left;
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final Token operator;
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final Expr right;
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}
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static class Unary extends Expr {
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Unary(Token operator, Expr right) {
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this.operator = operator;
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@ -79,6 +79,19 @@ public class Interpreter implements Expr.Visitor<Object>,
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return expr.value;
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}
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@Override
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public Object visitLogicalExpr(Expr.Logical expr) {
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Object left = evaluate(expr.left);
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if (expr.operator.type == TokenType.OR) {
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if (isTruthy(left)) return left;
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} else {
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if (!isTruthy(left)) return left;
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}
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return evaluate(expr.right);
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}
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@Override
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public Object visitUnaryExpr(Expr.Unary expr) {
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Object right = evaluate(expr.right);
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@ -171,6 +184,16 @@ public class Interpreter implements Expr.Visitor<Object>,
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return null;
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}
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@Override
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public Void visitIfStmt(Stmt.If stmt) {
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if (isTruthy(evaluate(stmt.condition))) {
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execute(stmt.thenBranch);
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} else if (stmt.elseBranch != null) {
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execute(stmt.elseBranch);
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}
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return null;
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}
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@Override
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public Void visitPrintStmt(Stmt.Print stmt) {
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Object value = evaluate(stmt.expression);
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@ -188,4 +211,12 @@ public class Interpreter implements Expr.Visitor<Object>,
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environment.define(stmt.name.lexeme, value);
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return null;
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}
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@Override
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public Void visitWhileStmt(Stmt.While stmt) {
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while (isTruthy(evaluate(stmt.condition))) {
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execute(stmt.body);
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}
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return null;
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}
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}
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@ -1,12 +1,14 @@
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package lox;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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import static lox.TokenType.*;
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public class Parser {
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private static class ParseError extends RuntimeException {}
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private static class ParseError extends RuntimeException {
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}
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private final List<Token> tokens;
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private int current;
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@ -40,12 +42,71 @@ public class Parser {
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}
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private Stmt statement() {
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if (match(FOR)) return forStatement();
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if (match(IF)) return ifStatement();
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if (match(PRINT)) return printStatement();
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if (match(WHILE)) return whileStatement();
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if (match(LEFT_BRACE)) return new Stmt.Block(block());
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return expressionStatement();
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}
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private Stmt forStatement() {
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consume(LEFT_PAREN, "Expect '(' after 'for'.");
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Stmt initializer;
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if (match(SEMICOLON)) {
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initializer = null;
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} else if (match(VAR)) {
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initializer = varDeclaration();
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} else {
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initializer = expressionStatement();
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}
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Expr condition = null;
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if (!check(SEMICOLON)) {
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condition = expression();
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}
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consume(SEMICOLON, "Expect ';' after loop condition.");
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Expr increment = null;
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if (!check(RIGHT_PAREN)) {
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increment = expression();
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}
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consume(RIGHT_PAREN, "Expect ')' after for clauses.");
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Stmt body = statement();
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if (increment != null) {
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body = new Stmt.Block(
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Arrays.asList(
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body,
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new Stmt.Expression(increment)));
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}
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if (condition == null) condition = new Expr.Literal(true);
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body = new Stmt.While(condition, body);
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if (initializer != null) {
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body = new Stmt.Block(Arrays.asList(initializer, body));
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}
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return body;
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}
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private Stmt ifStatement() {
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consume(LEFT_PAREN, "Expect '(' after 'if'.");
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Expr condition = expression();
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consume(RIGHT_PAREN, "Expect ')' after if condition.");
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Stmt thenBranch = statement();
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Stmt elseBranch = null;
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if (match(ELSE)) {
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elseBranch = statement();
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}
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return new Stmt.If(condition, thenBranch, elseBranch);
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}
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private Stmt printStatement() {
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Expr value = expression();
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consume(SEMICOLON, "Expect ';' after value.");
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@ -64,6 +125,15 @@ public class Parser {
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return new Stmt.Var(name, initializer);
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}
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private Stmt whileStatement() {
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consume(LEFT_PAREN, "Expect '(' after 'while'.");
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Expr condition = expression();
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consume(RIGHT_PAREN, "Expect ')' after condition.");
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Stmt body = statement();
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return new Stmt.While(condition, body);
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}
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private Stmt expressionStatement() {
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Expr expr = expression();
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consume(SEMICOLON, "Expect ';' after expression.");
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@ -82,7 +152,7 @@ public class Parser {
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}
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private Expr assignment() {
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Expr expr = equality();
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Expr expr = or();
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if (match(EQUAL)) {
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Token equals = previous();
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@ -93,7 +163,31 @@ public class Parser {
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return new Expr.Assign(name, value);
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}
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error(equals, "Invalid assignment target.");
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throw error(equals, "Invalid assignment target.");
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}
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return expr;
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}
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private Expr or() {
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Expr expr = and();
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while (match(OR)) {
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Token operator = previous();
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Expr right = and();
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expr = new Expr.Logical(expr, operator, right);
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}
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return expr;
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}
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private Expr and() {
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Expr expr = equality();
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while (match(AND)) {
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Token operator = previous();
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Expr right = equality();
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expr = new Expr.Logical(expr, operator, right);
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}
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return expr;
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@ -6,8 +6,10 @@ abstract class Stmt {
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interface Visitor<R> {
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R visitBlockStmt(Block stmt);
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R visitExpressionStmt(Expression stmt);
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R visitIfStmt(If stmt);
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R visitPrintStmt(Print stmt);
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R visitVarStmt(Var stmt);
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R visitWhileStmt(While stmt);
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}
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static class Block extends Stmt {
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Block(List<Stmt> statements) {
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@ -33,6 +35,22 @@ abstract class Stmt {
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final Expr expression;
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}
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static class If extends Stmt {
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If(Expr condition, Stmt thenBranch, Stmt elseBranch) {
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this.condition = condition;
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this.thenBranch = thenBranch;
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this.elseBranch = elseBranch;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitIfStmt(this);
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}
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final Expr condition;
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final Stmt thenBranch;
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final Stmt elseBranch;
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}
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static class Print extends Stmt {
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Print(Expr expression) {
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this.expression = expression;
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@ -59,6 +77,20 @@ abstract class Stmt {
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final Token name;
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final Expr initializer;
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}
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static class While extends Stmt {
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While(Expr condition, Stmt body) {
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this.condition = condition;
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this.body = body;
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}
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@Override
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<R> R accept(Visitor<R> visitor) {
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return visitor.visitWhileStmt(this);
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}
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final Expr condition;
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final Stmt body;
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}
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abstract <R> R accept(Visitor<R> visitor);
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}
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@ -18,6 +18,7 @@ public class GenerateAst {
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"Binary : Expr left, Token operator, Expr right",
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"Grouping : Expr expression",
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"Literal : Object value",
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"Logical : Expr left, Token operator, Expr right",
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"Unary : Token operator, Expr right",
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"Variable : Token name"
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));
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@ -25,8 +26,11 @@ public class GenerateAst {
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defineAst(outputDir, "Stmt", Arrays.asList(
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"Block : List<Stmt> statements",
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"Expression : Expr expression",
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"If : Expr condition, Stmt thenBranch," +
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" Stmt elseBranch",
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"Print : Expr expression",
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"Var : Token name, Expr initializer"
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"Var : Token name, Expr initializer",
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"While : Expr condition, Stmt body"
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));
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}
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