Decode enum using Go

Hi, with the Go lib https://github.com/philandstuff/dhall-golang

Could you give me an example on how to decode an enum (union with all empty alternatives) into a Go structure?

Dhall:

let Day =
      < Monday | Tuesday | ... >

Go:

type Thing struct {
   Name string `dhall:"name"`
   Day ????? `dhall:"day"`  <-- what goes here?
}

Thanks