anchor.diff:    NativeCode(this.code);
   }
   
  -abstract class NumberLiteral<T> extends Expression {
  +abstract class NumberLiteral<T extends num> extends Expression {
     static NumberLiteral create(num value) {
       if (value is double) {
         return new DoubleLiteral(value);
  
positive.code: 
    bool get isTrue => value == true;
    bool get isFalse => value == false;
  }
  
  class NamespaceBlock extends Statement {
  
negative.code:   }
  
    T get value;
  
    NumberLiteral<T> abs() => NumberLiteral.create(value.abs());
  }
  
  class IntegerLiteral extends NumberLiteral<int> {
  