{-|

TODO: Support `< When : { condition : Text, fields : a } | If { … } >` in
      future. This isn’t currently possible because for the non-`else` variant,
      `hpack` wants the fields to be merged with the `condition`. Address this
      once Dhall has row types, or we get away from hpack as an intermediary.
-}
λ(a : Type) → { condition : Text, `then` : a, `else` : a }