type 'a t = | Exact of Base.string | 
| Output | 
| Pretty of 'a | 
| Unreachable | 
val sexp_of_t : ('a -> Expect_test_common__.Import.Ppx_sexp_conv_lib.Sexp.t) -> 'a t -> Expect_test_common__.Import.Ppx_sexp_conv_lib.Sexp.tval map_pretty : 'a t -> f:('a -> 'b) -> 'b t