anchor.diff:      return visit(node.expression)(ek, (expr) {
         addStatement(make.methodInvocation(expr, 'then',
             [_reifyAwaitContinuation(sk, ek),
  -           make.namedExpression('onError', ek)]));
  +           make.namedExpression('onError', ek.reify())]));
       });
     };
   
  
positive.code: 
      var exceptionName = newName('e');
      var stackTraceName = newName('s');
      var catchBlock;
      if (catchName != null) {
        catchBlock = make.block([make.functionInvocation(catchName,
            [make.identifier(exceptionName), make.identifier(stackTraceName)])]);
      } else {
        catchBlock = make.block([make.functionInvocation(ek,
            [make.identifier(exceptionName), make.identifier(stackTraceName)])]);
      }
      addStatement(make.tryStatement(tryBlock,
          [make.catchClause(null, exceptionName, stackTraceName, catchBlock)]));
    };
  
negative.code:     visit(node.block)((v) {
        addStatement(make.methodInvocation(make.identifier(completerName),
            'complete', [v]));
      }, new NamedErrorContinuation(completerName, 'completeError'), () {
        addStatement(make.methodInvocation(make.identifier(completerName),
            'complete', []));
      });
  