Re: [Caml-list] toplevel with pre-installed printers

[Jean-Christophe Filliatre <filliatr@lri.fr>]

Hello,

Andrej Bauer writes:
 > This seems like a trivial question, but I do not know the answer:
 > how do I create either a toplevel (or a shell script which appears to be
 > a toplevel) with pre-installed pretty-printers (and pre-opened modules,
 > for that matter)?

I learnt a trick to do that from David Monniaux's GMP interface.

First define  your pretty-printers using the Ocaml  module Format. For
instance, the GMP pretty-printers look like

== gmp_pp.ml =========================================================
open Gmp
open Format
let z z = print_string (Z.string_from z)
let q q = ...
======================================================================

then introduce another file installing the pretty-printers:

== install_gmp_pp.ml =================================================
(* This is a hack to install the pretty-printers in the customized toplevel. *)

(* Caml longidents. *)
type t =
  | Lident of string
  | Ldot of t * string
  | Lapply of t * t

let _ = Topdirs.dir_directory "+creal"

let _ = Topdirs.dir_install_printer Format.std_formatter 
	  (Obj.magic (Ldot (Lident "Gmp_pp", "z")) : 'a)

let _ = Topdirs.dir_install_printer Format.std_formatter 
	  (Obj.magic (Ldot (Lident "Gmp_pp", "q")) : 'a)
======================================================================

Finally,  build your  ocaml toplevel  the usual  way, linking  the two
files above:

======================================================================
ocamlgmp: gmp.cma gmp_pp.cmo install_gmp_pp.cmo
	ocamlmktop -custom -o $@ $^
======================================================================

I know  this is a  hack (the infamous  Obj.magic is used and  the Caml
longident  type could change  in a  next ocaml  version) but  it works
fine.

Hope this helps,
-- 
Jean-Christophe Filliâtre (http://www.lri.fr/~filliatr)