Felix using and being called from GTK+3

gtk.flx

export requires header """ #include <gtk/gtk.h> """, package "gtk";

type GtkApplication_ptr = "GtkApplication*";
type GtkWidget_ptr = "GtkWidget*";
type gpointer = "gpointer";

cproc hello (widget:GtkWidget_ptr, data:gpointer) = {                                                                                                                                                                     [21/1899]

    var text = cexpr [+char] """
            (char*) gtk_entry_buffer_get_text(
                gtk_entry_get_buffer( (GtkEntry*) $1 )
            )
    """ (data) endcexpr;

    println$ "hello from felix: " + text;
}

cproc destroy () = {
    cstmt """ gtk_main_quit (); """;
}

cproc activate (app:GtkApplication_ptr, user_data:gpointer) = {
    cstmt """
        auto window =
            gtk_application_window_new ($1);

        auto button_box = 
            gtk_button_box_new (GTK_ORIENTATION_VERTICAL);
            
        gtk_container_add (GTK_CONTAINER (window), button_box);

        auto button = 
            gtk_button_new_with_label ("Hello Felix");

        auto tf  = 
            gtk_entry_new ();

        g_signal_connect (button, "clicked", G_CALLBACK ($2), tf);

        gtk_container_add (GTK_CONTAINER (button_box), button);
        gtk_container_add (GTK_CONTAINER (button_box), tf);

        gtk_window_set_title (GTK_WINDOW (window), "Felix Window");
        gtk_window_set_default_size (GTK_WINDOW (window), 200, 200);
        gtk_widget_show_all (window);
    """ 
    (app, hello)
    ;
}


proc init_app() = {
    cstmt """
        auto app = 
            gtk_application_new ("org.gtk.example", G_APPLICATION_FLAGS_NONE);

        g_signal_connect (app, "activate", G_CALLBACK ($3), NULL);

        int status = 
            g_application_run (G_APPLICATION (app), $1, $2);

        g_object_unref (app);

    """ 
    (System::argc, System::_argv, activate) 
    ;
}
init_app();

Makefile

.PHONY: test

test: gtk.fpc
    flx --pkgconfig-path+=. --static -o app gtk.flx

gtk.fpc:
    echo "cflags: `pkg-config --cflags gtk+-3.0`" > gtk.fpc
    echo "requires_slibs: `pkg-config --libs gtk+-3.0`" >> gtk.fpc