code: func (v *evalVisitor) isHelperCall(node *ast.Expression) bool {
  	if helperName := node.HelperName(); helperName != "" {
  		return v.findHelper(helperName) != zero
  	}
  	return false
  }
docs: //
  // Helpers
  //
  // isHelperCall returns true if given expression is a helper call