Exactly! This is why Lisp has dynamic variables: (let ((*emailer* mailgun-client)) (send email)) Or, using Go contexts (which are just a way of hack

Exactly! This is why Lisp has dynamic variables: (let ((*emailer* mailgun-client)) (send email)) Or, using Go contexts (which are just a way of hacking in dynamic variables): ctx = email.NewContext(ctx, mailgunClient) email.Send(ctx) And in email.Send: emailer, ok := EmailerFromContext(ctx) if !ok { emailer = defaultSMTPEmailer }