Date: Thu, 12 Aug 2004 13:17:18 +0200 (CEST)
Message-Id: <20040812.131718.74755885.oandrieu at nerim.net>
To: seguso.forever at tin.it
Cc: lablgtk at kaba.or.jp
Subject: Re: (errata corrige) Screen for GtkWindow not set --- Warning:
 this expression should have type unit.
From: Olivier Andrieu <andrieu at ijm.jussieu.fr>
In-Reply-To: <200408091552.53159.seguso.forever at tin.it>
References: <200408091552.53159.seguso.forever at tin.it>
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Hi,

 Maurizio Colucci [Mon, 9 Aug 2004]:
 > [in my previous message I forgot to say what the warnings are]
 > 
 > Hello,
 > 
 > I am trying to write an adventure game with lablgtk2 and lablgl.  I
 > have installed debian sid which seemed to have a good support for
 > ocaml.  Unfortunately I am getting warnings and runtime errors when
 > compiling hello world.
 > 
 > This is the program I am trying to compile (hello.ml):
 > 
 > 
 > open GMain
 > 
 > let window = GWindow.window ~border_width: 10 ()
 > 
 > let button = GButton.button ~label:"Hello World" ~packing: window#add ()
 > 
 > let main () =
 >   window#event#connect#delete 
 >     ~callback:(fun _ -> prerr_endline "Delete event occured"; true);
 >   window#connect#destroy ~callback:Main.quit;
 >   button#connect#clicked ~callback:(fun () -> prerr_endline "Hello World");
 >   button#connect#clicked ~callback:window#destroy;
 >   window#show ();
 >   Main.main ()
 > 
 > let _ = Printexc.print main ()
 > 
 > 
 > This is the Makefile I am using (written by me after reading the ocaml 
 > manual):
 > 
 > 
 > all: hello.ml
 > 	ocamlc -I /usr/lib/ocaml/3.08/lablgl -I /usr/lib/ocaml/3.08/lablgtk2 
 > lablgtk.cma lablgl.cma lablgtkgl.cma  hello.ml
 > 
 > 
 > I am getting these warnings:
 > 
 > ocamlc -I /usr/lib/ocaml/3.08/lablgl -I /usr/lib/ocaml/3.08/lablgtk2  
 > lablgtk.cma lablgl.cma  adv.ml
 > File "adv.ml", line 36, characters 2-52:
 > Warning: this expression should have type unit.
 > File "adv.ml", line 37, characters 2-42:
 > Warning: this expression should have type unit.
 > File "adv.ml", line 39, characters 2-40:
 > Warning: this expression should have type unit.
 > File "adv.ml", line 40, characters 2-49:
 > Warning: this expression should have type unit.

that's because connecting signals returns a GtkSignal.id (it can be
used to deconnect a signal). In your program you are discarding this
value so ocaml emits a warning. Either compile your code with -w s or
write it like this:

  let _ = window#connect#destroy ~callback:Main.quit in
  let _ = button#connect#clicked ...

 > 
 > I don't understand the warnings. however, the program compiles
 > despite the warnings, but at runtime I am getting these errors:

[snip]

you did not init GTK+. See the README:

,----[ README ]
| lablgtktop contains an extra module GtkInit, whose only contents is:
|       let locale = GtkMain.Main.init ()
| You must either add this line, or add this module to your link,
| before calling any Gtk function.
| ocamlc -I +lablgtk2 -w s lablgtk.cma gtkInit.cmo ???.ml -o ???
`----

-- 
   Olivier