add experimental reload feature

This is a first crude attempt at allowing reloading without exiting
fped. This should be useful when writing a design as text and using
the GUI only to visualize it.

Reload is only enabled (in the File menu) if the file doesn't have
the "MACHINE-GENERATED" header.

Known bugs:
- exits on parse errors
- leaks memory badly
- current frame is reset to root

fpd.h

@@ -26,6 +26,7 @@ extern struct value *var_value_list;
 int dbg_print(const struct expr *expr, const struct frame *frame);
 
 void scan_empty(void);
+void scan_file(void);
 void scan_expr(const char *s);
 void scan_var(const char *s);
 void scan_values(const char *s);

fpd.l

@@ -35,6 +35,12 @@ void scan_empty(void)
 }
 
 
+void scan_file(void)
+{
+	start_token = START_FPD;
+}
+
+
 void scan_expr(const char *s)
 {
 	start_token = START_EXPR;

fped.c

@@ -64,6 +64,21 @@ static void load_file(const char *name)
 }
 
 
+void reload(void)
+{
+	struct frame *old_frames;
+
+	/* @@@ this needs more work */
+	purge();
+	old_frames = frames;
+	scan_file();
+	load_file(save_file_name);
+	if (!instantiate())
+		frames = old_frames;
+	change_world();
+}
+
+
 static void usage(const char *name)
 {
 	fprintf(stderr,

fped.h

@@ -1,8 +1,8 @@
 /*
  * fped.h - Things fped.c exports
  *
- * Written 2010 by Werner Almesberger
- * Copyright 2010 by Werner Almesberger
+ * Written 2010, 2012 by Werner Almesberger
+ * Copyright 2010, 2012 by Werner Almesberger
  *
  * This program is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -17,4 +17,7 @@
 extern char *save_file_name;
 extern int no_save;
 
+
+void reload(void);
+
 #endif /* !FPED_H */

gui.c

@@ -102,6 +102,8 @@ static GtkItemFactoryEntry menu_entries[] = {
         { "/File/Write Postscript",
 				NULL,	write_ps,	0, "<Item>" },
         { "/File/sep2",		NULL,	NULL,		0, "<Separator>" },
+        { "/File/Reload",	NULL,	reload,		0, "<Item>" },
+        { "/File/sep3",		NULL,	NULL,		0, "<Separator>" },
         { "/File/Quit",		NULL,	gtk_main_quit,	0, "<Item>" },
 	{ "/View",		NULL,	NULL,		0, "<Branch>" },
 	{ "/View/Zoom in",	NULL,	zoom_in_center,	0, "<Item>" },
@@ -127,6 +129,9 @@ static void make_menu_bar(GtkWidget *hbox)
 
 	gtk_widget_set_sensitive(
 	    gtk_item_factory_get_item(factory, "/File/Save"), !no_save);
+	gtk_widget_set_sensitive(
+	    gtk_item_factory_get_item(factory, "/File/Reload"),
+	    no_save && !!save_file_name);
 }