Control flow chapter

src/lox/AstPrinter.java

@@ -27,6 +27,11 @@ public class AstPrinter implements Expr.Visitor<String> {
         return expr.value.toString();
     }
 
+    @Override
+    public String visitLogicalExpr(Expr.Logical expr) {
+        return parethesize(expr.operator.lexeme, expr.left, expr.right);
+    }
+
     @Override
     public String visitUnaryExpr(Expr.Unary expr) {
         return parethesize(expr.operator.lexeme, expr.right);

src/lox/Expr.java

@@ -8,6 +8,7 @@ abstract class Expr {
 		R visitBinaryExpr(Binary expr);
 		R visitGroupingExpr(Grouping expr);
 		R visitLiteralExpr(Literal expr);
+		R visitLogicalExpr(Logical expr);
 		R visitUnaryExpr(Unary expr);
 		R visitVariableExpr(Variable expr);
 	}
@@ -65,6 +66,22 @@ abstract class Expr {
 
 		final Object value;
 	}
+	static class Logical extends Expr {
+		Logical(Expr left, Token operator, Expr right) {
+			this.left = left;
+			this.operator = operator;
+			this.right = right;
+		}
+
+		@Override
+		<R> R accept(Visitor<R> visitor) {
+			return visitor.visitLogicalExpr(this);
+		}
+
+		final Expr left;
+		final Token operator;
+		final Expr right;
+	}
 	static class Unary extends Expr {
 		Unary(Token operator, Expr right) {
 			this.operator = operator;

src/lox/Interpreter.java

@@ -79,6 +79,19 @@ public class Interpreter implements Expr.Visitor<Object>,
         return expr.value;
     }
 
+    @Override
+    public Object visitLogicalExpr(Expr.Logical expr) {
+        Object left = evaluate(expr.left);
+
+        if (expr.operator.type == TokenType.OR) {
+            if (isTruthy(left)) return left;
+        } else {
+            if (!isTruthy(left)) return left;
+        }
+
+        return evaluate(expr.right);
+    }
+
     @Override
     public Object visitUnaryExpr(Expr.Unary expr) {
         Object right = evaluate(expr.right);
@@ -171,6 +184,16 @@ public class Interpreter implements Expr.Visitor<Object>,
         return null;
     }
 
+    @Override
+    public Void visitIfStmt(Stmt.If stmt) {
+        if (isTruthy(evaluate(stmt.condition))) {
+            execute(stmt.thenBranch);
+        } else if (stmt.elseBranch != null) {
+            execute(stmt.elseBranch);
+        }
+        return null;
+    }
+
     @Override
     public Void visitPrintStmt(Stmt.Print stmt) {
         Object value = evaluate(stmt.expression);
@@ -188,4 +211,12 @@ public class Interpreter implements Expr.Visitor<Object>,
         environment.define(stmt.name.lexeme, value);
         return null;
     }
+
+    @Override
+    public Void visitWhileStmt(Stmt.While stmt) {
+        while (isTruthy(evaluate(stmt.condition))) {
+            execute(stmt.body);
+        }
+        return null;
+    }
 }

src/lox/Parser.java

@@ -1,12 +1,14 @@
 package lox;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 import static lox.TokenType.*;
 
 public class Parser {
-    private static class ParseError extends RuntimeException {}
+    private static class ParseError extends RuntimeException {
+    }
 
     private final List<Token> tokens;
     private int current;
@@ -40,12 +42,71 @@ public class Parser {
     }
 
     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.");
@@ -64,6 +125,15 @@ public class Parser {
         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.");
@@ -82,7 +152,7 @@ public class Parser {
     }
 
     private Expr assignment() {
-        Expr expr = equality();
+        Expr expr = or();
 
         if (match(EQUAL)) {
             Token equals = previous();
@@ -93,7 +163,31 @@ public class Parser {
                 return new Expr.Assign(name, value);
             }
 
-            error(equals, "Invalid assignment target.");
+            throw 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;

src/lox/Stmt.java

@@ -6,8 +6,10 @@ abstract class Stmt {
 	interface Visitor<R> {
 		R visitBlockStmt(Block stmt);
 		R visitExpressionStmt(Expression stmt);
+		R visitIfStmt(If stmt);
 		R visitPrintStmt(Print stmt);
 		R visitVarStmt(Var stmt);
+		R visitWhileStmt(While stmt);
 	}
 	static class Block extends Stmt {
 		Block(List<Stmt> statements) {
@@ -33,6 +35,22 @@ abstract class Stmt {
 
 		final Expr expression;
 	}
+	static class If extends Stmt {
+		If(Expr condition, Stmt thenBranch, Stmt elseBranch) {
+			this.condition = condition;
+			this.thenBranch = thenBranch;
+			this.elseBranch = elseBranch;
+		}
+
+		@Override
+		<R> R accept(Visitor<R> visitor) {
+			return visitor.visitIfStmt(this);
+		}
+
+		final Expr condition;
+		final Stmt thenBranch;
+		final Stmt elseBranch;
+	}
 	static class Print extends Stmt {
 		Print(Expr expression) {
 			this.expression = expression;
@@ -59,6 +77,20 @@ abstract class Stmt {
 		final Token name;
 		final Expr initializer;
 	}
+	static class While extends Stmt {
+		While(Expr condition, Stmt body) {
+			this.condition = condition;
+			this.body = body;
+		}
+
+		@Override
+		<R> R accept(Visitor<R> visitor) {
+			return visitor.visitWhileStmt(this);
+		}
+
+		final Expr condition;
+		final Stmt body;
+	}
 
 	abstract <R> R accept(Visitor<R> visitor);
 }

src/tool/GenerateAst.java

@@ -18,6 +18,7 @@ public class GenerateAst {
                 "Binary   : Expr left, Token operator, Expr right",
                 "Grouping : Expr expression",
                 "Literal  : Object value",
+                "Logical  : Expr left, Token operator, Expr right",
                 "Unary    : Token operator, Expr right",
                 "Variable : Token name"
         ));
@@ -25,8 +26,11 @@ public class GenerateAst {
         defineAst(outputDir, "Stmt", Arrays.asList(
                 "Block      : List<Stmt> statements",
                 "Expression : Expr expression",
+                "If         : Expr condition, Stmt thenBranch," +
+                            " Stmt elseBranch",
                 "Print      : Expr expression",
-                "Var        : Token name, Expr initializer"
+                "Var        : Token name, Expr initializer",
+                "While      : Expr condition, Stmt body"
         ));
     }