add while loops

Author: Boxfort

README.md

@@ -11,11 +11,12 @@ declaration    -> varDecl | statement ;
 
 varDecl        -> "var" IDENTIFIER ( "=" expression )? ";" ;
 
-statement      -> exprStmt | ifStmt | printStmt | block;
+statement      -> exprStmt | ifStmt | printStmt | whileStmt | block;
 
 exprStmt       -> expression ";" ;
 ifStmt         -> "if" "(" expression ")" statement ( "else" statement )? ;
 printStmt      -> "print" expression ";" ;
+whileStmt      -> "while "(" expression ")" statement ;
 block          -> "{" declaration* "}" ;
 
 expression     -> assignment ;

src/com/boxfort/jlox/Interpreter.java

@@ -84,6 +84,14 @@ public Void visitVarStmt(Stmt.Var stmt) {
         return null;
     }
 
+    @Override
+    public Void visitWhileStmt(Stmt.While stmt) {
+        while(isTruthy(evaluate(stmt.condition))) {
+            execute(stmt.body);
+        }
+        return null;
+    }
+
     @Override
     public Object visitAssignExpr(Expr.Assign expr) {
         Object value = evaluate(expr.value);

src/com/boxfort/jlox/Parser.java

@@ -52,6 +52,7 @@ private Stmt varDeclaration() {
     private Stmt statement() {
         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();
@@ -78,6 +79,15 @@ private Stmt printStatement() {
         return new Stmt.Print(value);
     }
 
+    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.");

src/com/boxfort/jlox/Stmt.java

@@ -9,6 +9,7 @@ interface Visitor<R> {
         R visitIfStmt(If stmt);
         R visitPrintStmt(Print stmt);
         R visitVarStmt(Var stmt);
+        R visitWhileStmt(While stmt);
     }
 
     static class Block extends Stmt {
@@ -82,5 +83,20 @@ <R> R accept(Visitor<R> visitor) {
         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/com/boxfort/tool/GenerateAst.java

@@ -28,7 +28,8 @@ public static void main(String[] args) throws IOException {
             "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"
         ));
     }