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
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.