$ ocaml -I +lablgtk2 lablgtk.cma
        Objective Caml version 3.10.0

# #load "hello.ml";;
File hello.ml is not a bytecode object file.
# #use "hello.ml";;

(process:15489): GLib-GObject-WARNING **: invalid (NULL) pointer instance

(process:15489): GLib-GObject-CRITICAL **: g_signal_connect_data: assertion `G_TYPE_CHECK_INSTANCE (instance)' failed
val window : GWindow.window = <obj>
val button : GButton.button = <obj>
File "hello.ml", line 10, characters 2-98:
Warning S: this expression should have type unit.
File "hello.ml", line 12, characters 2-44:
Warning S: this expression should have type unit.
File "hello.ml", line 13, characters 2-74:
Warning S: this expression should have type unit.
File "hello.ml", line 14, characters 2-49:
Warning S: this expression should have type unit.
val main : unit -> unit = <fun>

(process:15489): Gtk-WARNING **: Screen for GtkWindow not set; you must always set
a screen for a GtkWindow before using the window

(process:15489): Gdk-CRITICAL **: gdk_pango_context_get_for_screen: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Pango-CRITICAL **: pango_context_set_font_description: assertion `context != NULL' failed

(process:15489): Pango-CRITICAL **: pango_context_set_base_dir: assertion `context != NULL' failed

(process:15489): Pango-CRITICAL **: pango_context_set_language: assertion `context != NULL' failed

(process:15489): Pango-CRITICAL **: pango_layout_new: assertion `context != NULL' failed

(process:15489): Pango-CRITICAL **: pango_layout_set_text: assertion `layout != NULL' failed

(process:15489): Pango-CRITICAL **: pango_layout_set_alignment: assertion `layout != NULL' failed

(process:15489): Pango-CRITICAL **: pango_layout_set_ellipsize: assertion `PANGO_IS_LAYOUT (layout)' failed

(process:15489): Pango-CRITICAL **: pango_layout_set_single_paragraph_mode: assertion `PANGO_IS_LAYOUT (layout)' failed

(process:15489): Pango-CRITICAL **: pango_layout_set_width: assertion `layout != NULL' failed

(process:15489): Pango-CRITICAL **: pango_layout_get_extents: assertion `layout != NULL' failed

(process:15489): Gtk-WARNING **: gtk_widget_size_allocate(): attempt to allocate widget with width 30 and height -1187434

(process:15489): Gdk-CRITICAL **: gdk_screen_get_default_colormap: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Gdk-CRITICAL **: gdk_colormap_get_visual: assertion `GDK_IS_COLORMAP (colormap)' failed

(process:15489): Gdk-CRITICAL **: gdk_screen_get_default_colormap: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Gdk-CRITICAL **: gdk_screen_get_root_window: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Gdk-CRITICAL **: gdk_screen_get_root_window: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_new: assertion `GDK_IS_WINDOW (parent)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_enable_synchronized_configure: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_user_data: assertion `window != NULL' failed

(process:15489): Gtk-CRITICAL **: gtk_style_attach: assertion `window != NULL' failed

(process:15489): Gtk-CRITICAL **: gtk_style_set_background: assertion `GTK_IS_STYLE (style)' failed

(process:15489): Gtk-CRITICAL **: gtk_paint_flat_box: assertion `GTK_IS_STYLE (style)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_accept_focus: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_focus_on_map: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_modal_hint: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gtk-CRITICAL **: gtk_window_realize_icon: assertion `widget->window != NULL' failed

(process:15489): Gtk-WARNING **: Screen for GtkWindow not set; you must always set
a screen for a GtkWindow before using the window

(process:15489): Gdk-CRITICAL **: gdk_window_set_geometry_hints: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_resize: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_freeze_toplevel_updates_libgtk_only: assertion `window != NULL' failed

(process:15489): Gdk-CRITICAL **: gdk_window_invalidate_maybe_recurse: assertion `window != NULL' failed

(process:15489): GLib-GObject-CRITICAL **: g_object_ref: assertion `G_IS_OBJECT (object)' failed

(process:15489): Gdk-CRITICAL **: gdk_screen_get_root_window: assertion `GDK_IS_SCREEN (screen)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_new: assertion `GDK_IS_WINDOW (parent)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_user_data: assertion `window != NULL' failed

(process:15489): Gtk-CRITICAL **: gtk_style_attach: assertion `window != NULL' failed

(process:15489): GLib-GObject-CRITICAL **: g_object_ref: assertion `G_IS_OBJECT (object)' failed

(process:15489): Gtk-CRITICAL **: gtk_style_attach: assertion `window != NULL' failed

(process:15489): Gdk-CRITICAL **: gdk_window_invalidate_rect: assertion `window != NULL' failed

(process:15489): Gdk-CRITICAL **: gdk_window_invalidate_rect: assertion `window != NULL' failed

(process:15489): Gdk-CRITICAL **: gdk_window_unmaximize: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_unstick: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_deiconify: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_unfullscreen: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_keep_above: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_set_keep_below: assertion `GDK_IS_WINDOW (window)' failed

(process:15489): Gdk-CRITICAL **: gdk_window_show: assertion `GDK_IS_WINDOW (window)' failed