Conversion.From_Arity
type !'r0 ar0 = D.Context.t -> 'r
type (!'a0, !'r0) ar1 = D.Context.t -> 'a -> 'r
type (!'a0, !'b0, !'r0) ar2 = D.Context.t -> 'a -> 'b -> 'r
type (!'a0, !'b0, !'c0, !'r0) ar3 = D.Context.t -> 'a -> 'b -> 'c -> 'r
type (!'a0, !'r0) variadic = D.Context.t -> 'a list -> 'r