RE: [Caml-list] baffled by semicolon

[briand@aracnet.com]

>>>>> "Alex" == Alex Valdez <alexandervaldez@sbcglobal.net> writes:

  Alex> The following code snippet

  Alex>  let w = area#misc#realize () ;

  Alex>    area#misc#window;;

  Alex> is the same as

  Alex>  let w = area#misc#realize ( () ; area#misc#window );;

interesting.  Somehow I managed to edit it poorly, in the file I
copied it from, the original statement is actuallly :

  let w = area#misc#realize () ; area#misc#window

and the next statement is a let, so the ;; is not really needed, I
just like to put them in for clarity.

  Alex> which is the same as

  Alex>  let w = area#misc#realize area#misc#window;;

Neither of the above works properly :

This expression has type Gdk.window = [ `drawable | `gdkwindow ] Gobject.obj
but is here used with type unit

However your response woke up some neurons - why wouldn't it be :

  let w = (area#misc#realize ()); area#misc#window ;;


Which also makes sense, the first statement being called for a
side-effect, and the second is the value for w.

ding-ding-ding we have a winner.  The above _does_ work.


Brian

  Alex> -----Original Message----- From:
  Alex> owner-caml-list@pauillac.inria.fr
  Alex> [mailto:owner-caml-list@pauillac.inria.fr]On Behalf Of
  Alex> briand@aracnet.com Sent: Wednesday, August 25, 2004 10:23 PM
  Alex> To: caml-list@pauillac.inria.fr Subject: [Caml-list] baffled
  Alex> by semicolon



  Alex> This might really by a lablgtk2 question, but I thought it's
  Alex> probably more of a ocaml syntax question :

  Alex> The following works :


  Alex> let window = GWindow.window ~width:400 ~height:400() ;;

  Alex> let area = GMisc.drawing_area ~packing:window#add () ;;

  Alex> let w = area#misc#realize () ;

  Alex>   area#misc#window;;

  Alex> let drawing = new GDraw.drawable w ;;

  Alex> However making the simple change

  Alex> let w = area#misc#realize () ;;

  Alex> ^^ notice the double semicolon gives an error: This expression
  Alex> has type unit but is here used with type [> `drawable ]
  Alex> Gobject.obj

  Alex> For the simple reason that w has somehow, mysteriously, become
  Alex> = () instead of Gdk.window which is the value it would acquire
  Alex> if it was only a single semi-colon.

  Alex> I went back through the manual and really couldn't find
  Alex> anything which explained the difference between ; and ;; - so
  Alex> it's not at all obvious to me what's going on here.  I would
  Alex> think that w would take on the value of evaluating

  Alex>  area#misc#realize ()

  Alex> in either case.

  Alex> ???

  Alex> Brian

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