anchor.diff:  class _ForEach extends Statement {
     final Var? variable;
     final Expression iterable;
  -  final List<Statement> body;
  +  final Statement body;
     final bool declaresVariable;
   
     _ForEach(this.variable, this.iterable, this.body, this.declaresVariable)
  
positive.code: 
  class _If extends Statement {
    final Expression condition;
    final List<Statement> ifTrue;
    final List<Statement>? ifFalse;
  
    _If(this.condition, this.ifTrue, this.ifFalse) : super._();
  
    @override
    String toString() =>
        'if ($condition) ${block(ifTrue)}' +
        (ifFalse == null ? '' : 'else ${block(ifFalse!)}');
  
    @override
    void _preVisit(AssignedVariables<Node, Var> assignedVariables) {
  
negative.code: 
    @override
    void _preVisit(AssignedVariables<Node, Var> assignedVariables) {
      for (var statement in statements) {
        statement._preVisit(assignedVariables);
      }
    }
  
    @override
    void _visit(
        Harness h, FlowAnalysis<Node, Statement, Expression, Var, Type> flow) {
      for (var statement in statements) {
        statement._visit(h, flow);
      }
    }
  }
  
  