anchor.diff:        }
         buff.write("}");
       }
  +    buff.write(")");
     }
   
     void visitWhileStatement(WhileStatement statement) {
  
positive.code:   }
  
    void visitBreakStatement(BreakStatement statement) {
      buff.write("break");
    }
  
    void visitAssignment(Assignment assignment) {
  
negative.code:       }
      """);
  
      addHelper("λvar", """
        function(context, name, value) {
          var m = value;
          Object.defineProperty(context, name, {
            enumerable: true,
            get: function() {
              return m;
            },
            set: function(v) {
              m = v;
            }
          });
        }
      """);
  
      addHelper("λfor", """
        function(b, v, λ) {
          for (var i = 0; i < v.length; i++) {
            var r = b(v[i], Object.create(λ));
            if (r === false) {
              return false;
            }
          }
        }
      """);
  
      addHelper("λwhile", """
        function(λ, c, t) {
          while (λbool(c)) {
            var r = t(Object.create(λ));
            if (r === false) {
              break;
            }
          }
        }
      """);
  
      addHelper("λif", """
        function(λ, c, t, f) {
          if (λbool(c)) {
            return t(Object.create(λ));
          } else if (typeof f !== "undefined") {
            return f(Object.create(λ));
          }
        }
      """);
  
      addHelper("λrange", """
        function(l, u) {
          var m = [];
          for (var i = l; i <= u; i++) {
            m.push(i);
          }
          return m;
        }
      """);
  
      addTopLevel("λbool", """
        function(value) {
          if (value === null || typeof value === "undefined") {
            return false;
  