code: func astVarToIdentifier(node ast.Node) (*ast.Identifier, bool) {
  	v, ok := node.(*ast.Var)
  	if ok {
  		return &v.Id, true
  	}
  	return nil, false
  }
docs: // in some cases it's convenient to parse something as an expression, and later
  // decide that it should be just an identifer