From: jeanmarc.eber@lexifi.com
To: caml-list@inria.fr
Date: Tue, 12 Jun 2001 16:53:21 +0200 (MEST) [thread overview]
Message-ID: <992357601.3b262ce14db42@imp.pro.proxad.net> (raw)
I just began to play seriously with Ocaml's toplevel and have the following
remarks and suggestions:
1. Standard use of the .ocamlinit file:
You have the possibility of "customising" the toplevel by a suitable
'.ocamlinit' file that is "#use"d before going in interactive mode.
Unfortunately, the '.ocamlinit' file isn't "#use"d in script mode, making it
impossible to create a *symmetric* environment for interactive and script mode.
I would suggest to "#use" also the ".ocamlinit" file in script mode (the result
being that it is put in front of your script file).
2. Type of user-defined printers:
The printing formatter system under OCaml is now everywhere in the compiler and
the standard libraries unified toward the "Format.formatter -> ('a,
Format.formatter, unit) format -> 'a type" approach, where all output functions
receive a formatter and a format string, giving everywhere these nice "fprintf
ppf "@[...@]" printo o ..." calls. This of course abstracts away the
destination of your output, that has to be parameterised by the choice of a
suitable formatter.
Unfortunately, user defined printers aren't of type Format.formatter -> ('a,
Format.formatter, unit) format -> 'a, but must be of type ('a,
Format.formatter, unit) format -> 'a. It seems (its not very clear from the
manual) that user-defined printers always have to print on
Format.std_formatter. Why ? I don't see any other explanation than historical
reasons... :-) I nethertheless suggest to unify also this last part of the
formatting system in OCaml. I don't think *many* OCaml users are using
industrially user defined printers and those who do could, I think, accept this
minor (and type tracked by the compiler!) change in their source.
Look at the relevant code in genprintval.ml (comments are mine):
let install_printer path ty fn = (* fn is the user defined printer *)
let print_val ppf obj = (* we have a ppf here *)
try fn obj with (* but we don't use it here !!!! *)
| exn ->
fprintf ppf "<printer %a raised an exception>" Printtyp.path path in
printers := (path, ty, print_val) :: !printers
3. Consequence: a minor subtle bug in OCaml's toplevel:
The following case isn't treated correctly under OCamls toplevel:
- you use "script" mode.
- your script raises an exception.
- your exception type contains one or more values that are printed by a custom
printer.
In this case, OCaml uses Format.err_formatter for its output (only for
exceptions, as other results aren't printed, of course), look at topmain.ml:
let file_argument name =
exit (if Toploop.run_script Format.err_formatter name Sys.argv then 0 else 2)
the exception will be printed on err_formatter, but calls recursively your
custom formatter that outputs on std_formatter... resulting in a not beautiful
"error message".
This shows how urgent it is to standardise *everywhere* on the same (powerful
and practical) formatting technology :-).
Jean-Marc Eber
LexiFi Technologies
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next reply other threads:[~2001-06-12 14:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-06-12 14:53 jeanmarc.eber [this message]
2001-07-03 11:18 ` [Caml-list] Re: improvements for the OCaml toplevel Xavier Leroy
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