idkinterface.re

module Query = [%graphql
  {|
    query { 
      someFieldWithInterfaceType {
        id
        ...on ImplA {
          a_only
        }
        ...on ImplB {
          b_only
        }
      }
    }
  |}
]

/* generated */
module Query = {
  type t = {.
    "someFieldWithInterfaceType": [
      | `ImplA ({. "id":string, "a_only": blah})
      | `ImplB ({. "id":string, "b_only": blah})
    ] 
  }
}