Idea found on the Circle Mailing List.
Callback functions - Parsing Single Line/Menu Input through STATE()'s
Callback v.1.0 -- 6/10/01

Idea by Jim Persson (jim@LINUX.NU) - he's a sort of newbie :-)
Mailer code by Mike Breuer (mbreuer@new.rr.com)
Adjustments and modifications by Akuma -- me (doomer18@hotmail.com)

Well, all that's needed is modifications to a few files.
======================
in structs.h after '#define SPECIAL(name) \' add this
---
#define C_FUNC(name) \
	void (name) (struct descriptor_data *d, char *arg, void *info)
---
later in the same file in 'struct descriptor_data {' at the end
---
   C_FUNC(*callback);		// Call back function for anything I want to do
   void *c_data;		// Storage for the Callback function
};
======================
in utils.h after 'int num_pc_in_room(struct room_data *room);'
---
void    line_input(struct descriptor_data *d, const char *prompt,
                   C_FUNC(*callback), void *info);
void    clean_callback(struct descriptor_data *d);
======================
in interpreter.c:nanny() after 'case CON_CLOSE:'
---
+  case CON_LINE_INPUT:
+    if (d->callback)
+      d->callback(d, arg, d->c_data);
+    else {
+      log("SYSERR: No callback function specified for state CON_LINE_INPUT");
+      STATE(d) = CON_PLAYING;
+    }
+    break;
  default:
---
in interpreter.c  at the end of the file is good enough
---
+// Called like so from somewhere that you want to ask a question:
+// line_input(ch->desc, "Do you want to multi-class to warrior (Yes/No)? ",
+//                       parse_multiclass);
+// ONLY USE FROM CON_PLAYING STATE()'s!
+
+void line_input(struct descriptor_data *d, const char *prompt,
+                C_FUNC(*callback), void *info) {
+  d->callback = callback;
+  d->c_data = (char *)info;
+  STATE(d) = CON_LINE_INPUT;
+  SEND_TO_Q(prompt, d);
+}
+
+void clean_callback(struct descriptor_data *d) {
+ d->callback = NULL;
+ // I wouldn't recommend passing pointers to objects
+ // just use for str_duping strings.  It is possible though.
+
+ if (d->c_data) FREE(d->c_data);
+ d->c_data = NULL;
+
+ STATE(d) = CON_PLAYING;
+}
======================
And that's it!
If you want a test_func, just go somewhere in your code (or make a
testing command to see it in action) and add in this:
======================
at the top of the file your putting your test functions in
lets just say interpreter.c for now
---
+C_FUNC(test_func);
+C_FUNC(test_func_chain);
---
and later in the file (near the bottom if you choose)
---
+C_FUNC(test_func) {
+ sprintf(buf, "You typed '%s'!\r\n", arg);
+ SEND_TO_Q(buf, d);
+ d->c_data = NULL;
+ line_input(d, "Type something else: ", test_func_chain, str_dup(arg));
+}
+
+C_FUNC(test_func_chain) {
+ sprintf(buf, "You typed '%s' and then '%s'... Cool.\r\n", (char *)info, arg);
+ SEND_TO_Q(buf, d);
+ // Call ONLY on the LAST function of a chain
+ clean_callback(d);
+}
======================


Now to call the functions and get the ball rolling, I used Jeremy Elson's
do_edit from his genolc package and just added in an extra case like so
(seeing as how I don't use the do_edit anyway)
======================
at the top of genolc.c after the '#include headers'
---
+C_FUNC(test_func);  // Don't need test_func_chain b/c it's called by this one
---
in do_edit add this in the switch() statement
---
   switch(a[0]) {
+  case 't':
+    line_input(ch->desc, "Test Function : Type something : ", test_func, NULL);
+    break;
   case 'a':
     save_all();
     break;
======================
Put this example in, compile, and when you log into the mud type :
edit t
It should send you to a prompt that tells you to 'Type something: '.  After
you do so, it'll give you another prompt to 'Type something else: '.
On both occasions, it will tell you exactly what you type.  

>Begin Example (I'll show what I type by preceding it with a '>':

edit t
Test function : Type something : >Testing, 1, 2, 3
You typed 'Testing, 1, 2, 3'!
Type something else: >Woo, It works :-)
You typed 'Testing 1, 2, 3' and then 'Woo, It works :-)'... Cool.

>End Example

And that's an example of how to use this properly... If someone has any
questions, feel free to email me about this :-)

Have fun with it

Akuma the Raging Coder