anchor.diff:            printStatement(null,
                 "Label ${block.name}, useCount=${block.label.useCount}");
           }
  +        if (block.catcher != null) {
  +          printStatement(null, 'Catch exceptions at ${block.catcher.name}');
  +        }
           block.statements.forEach(visitBlockMember);
         });
       });
  
positive.code: 
    visitIf(If node) {
      String condition = expr(node.condition);
      String thenTarget = collector.ifTargets[node.thenStatement].name;
      String elseTarget = collector.ifTargets[node.elseStatement].name;
      printStatement(null, "if $condition then $thenTarget else $elseTarget");
    }
  
  
negative.code:   // (if targets) to blocks.
    final Map<Label, Block> breakTargets = <Label, Block>{};
    final Map<Label, Block> continueTargets = <Label, Block>{};
    final Map<Statement, Block> substatements = <Statement, Block>{};
  
    Block catcher;
  
    void _addStatement(Statement statement) {
      blocks.last.statements.add(statement);
  