Date: Thu, 8 Sep 2005 07:35:58 -0300
From: romildo at uber.com.br
To: lablgtk at math.nagoya-u.ac.jp
Subject: Understanding "include" in lablGtk2 implementation
Message-ID: <20050908103558.GA21679 at malaquias>
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Hello.

In the process of writing a new OCaml interface to
an existing C library (gtkdatabox), I came acrros
some points in the lablGtk2 implementation that I
do not understand completly.

In the message
http://wwwfun.kurims.kyoto-u.ac.jp/soft/olabl/lablgtk-list/1016,
Jacques Garrigue gives some tips on implementing
a new lablGtk2 wrapper. Basically he tells to
look at an example for learning, and sugests
using the Text widget from GtkBroken. I am
following his sugestion.

In gtkBroken.ml there is the module definition

module Text = struct
  include Text
  (* ... *)
end

What is the phrase "include Text" used for here?
What does it mean?

The OCaml manual says the following about the include
expression:
(http://caml.inria.fr/pub/docs/manual-ocaml/manual018.html)

"The expression

    include module-type
		     
in a signature performs textual
inclusion of the components of the signature denoted by module-type. It
behaves as if the components of the included signature were copied at
the location of the include. The module-type argument must refer to a
module type that is a signature, not a functor type."

But the phrase used in gtkBroken.ml does not appear in a
signature, but in a structure. Where does the module type
"Text" come from?  Similar include expression are found on
other modules too.

When I try to mimic this expression in my own module

module Databox = struct
  include Databox
  (* ... *)
end

I get an error:

# make
ocamlc.opt -I +lablGL  -w s -c gtkDatabox.ml
File "gtkDatabox.ml", line 14, characters 10-17:
Unbound module Databox
make: *** [gtkDatabox.cmo] Error 2

Any comments?

Romildo