anchor.diff:    /// Return `true` if the current state is reachable.
     bool get isReachable;
   
  +  TypeOperations<Variable, Type> get typeOperations;
  +
     /// Call this method after visiting an "as" expression.
     ///
     /// [subExpression] should be the expression to which the "as" check was
  
positive.code:   bool get isReachable => true;
  
    @override
    void asExpression_end(Expression subExpression, Type type) {}
  
    @override
  
negative.code:         Expression extends Object, Variable extends Object, Type extends Object>
      implements FlowAnalysis<Node, Statement, Expression, Variable, Type> {
    /// The [TypeOperations], used to access types, and check subtyping.
    @override
    final TypeOperations<Variable, Type> typeOperations;
  
    /// Stack of [_FlowContext] objects representing the statements and
  