A list of pretty printers for various types, for use in toplevels.

Pretty_printer has a string list ref with the names of pp functions matching the interface:

      val pp : Format.formatter -> t -> unit

The names are actually OCaml identifier names, e.g. "Core.Date.pp". Code for building toplevels (this code is not in Core) evaluates the strings to yield the pretty printers and register them with OCaml runtime.

val all : unit -> string list
all () returns all pretty printers that have been registered.
val register : string -> unit
register name adds name to the list of pretty printers.
module type S = sig .. end
Modules that provide a pretty printer will match S.
type t
val pp : Format.formatter -> t -> unit
module Register : 
functor (M : sig .. end) -> S with type t := M.t
Register builds a pp function from a to_string function, and adds the module_name ^ ".pp" to the list of pretty printers. The idea is to statically guarantee that one has the desired pp function at the same point where the name is added.
module Register_pp : 
functor (M : sig .. end) -> S with type t := M.t
Register_pp is like Register, but allows a custom pp function rather than using to_string.