Any example on how to use the parser?

[jrb1989]

Is your feature request related to a problem?
I don't see how to use the parser

Describe the solution you'd like
Ideally, it would be very useful to include in the example project an example of the use of the parser found in the object:

  final MutationOptions options = MutationOptions(
      document: gql(mutation),
      variables: body, 
      parserFn: parser);