anchor.diff:  
     final List<ir.Definition> functionParameters = <ir.Definition>[];
   
  -  IrBuilderDelimitedState(this.constantSystem, this.currentElement);
  +  IrBuilderSharedState(this.constantSystem, this.currentElement);
   
     ir.Parameter get thisParameter => _thisParameter;
     void set thisParameter(ir.Parameter value) {
  
positive.code: 
    final List<ir.Parameter> _parameters = <ir.Parameter>[];
  
    IrBuilderDelimitedState state;
  
    /// A map from variable indexes to their values.
    ///
    /// [BoxLocal]s map to their box. [LocalElement]s that are boxed are not
    /// in the map; look up their [BoxLocal] instead.
    Environment environment;
  
    // The IR builder maintains a context, which is an expression with a hole in
    // it.  The hole represents the focus where new expressions can be added.
  
negative.code: abstract class IrBuilder {
    IrBuilder _makeInstance();
  
    void declareLocalVariable(LocalVariableElement element,
                              {ir.Primitive initialValue});
  
  