How to discover prefix keysequences?

[Marko Mahnic <marko.mahnic@xxxxxxxx>]

Hi.

I would like to implement Alt-key handling (for keys A..Z)
in FL-Jed in the following way:
   1. If Alt-<char> is bound to anything, pass "\e<char>" to JED
   2. If Alt-<char> is a prefix of a keysequence, pass "\e<char>" to JED
   3. Let FLTK handle Alt-XX

Curently I am using jed_get_key_function(buf, &s).
With it I can handle case 1 but not case 2.
If I assign "goto_line" to "\egl" (Alt-g l), I cannot
detect that Alt-g is used in a keysequence.

I can write a separate function (is_prefix_key) to return
the length of the prefix.

Alternatively jed_get_key_function can be modified to
return such info but only when the keystr parameter is
not NULL:

------- keymap.c, 1175
       key = SLang_do_key (CBuf->keymap, get_key_function_callback);
+      if (key == NULL)
+         return -1 - (Getkey_Callback_Data.num_read - 1)
    }

    if (key == NULL)
       return -1;
-----------------

(When keystr is NULL JED rads the key with jed_getkey;
if the keysequence is not assigned, the function
allways returns -1).

What other (SLang?) code would the change affect?
Is it better to modify jed_get_key_function or to
write is_prefix_key?


Example:

   setkey("goto_line", "\egl");
then

   1. jed_get_key_function("\002\eg", &s)
      returns -1 - 2
      which means "\eg" is a prefix sequence of length 2
   2. jed_get_key_function("\003\egf", &s)
      returns -1 - 2
      which means "\eg" is a prefix sequence, but "\egf" is not assigned
   3. jed_get_key_function("\003\egl", &s)
      returns 1..3
      which means "\egl" is assigned (current behaviour)


Marko

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