READ_KEY
     Waits for you to press a key and then returns the keyword for that key.
     The key is not echoed on the terminal screen.  Use READ_KEY instead of
     READ_CHAR when you are entering escape sequences, control codes, or
     other non-text characters.  READ_KEY processes escape sequences and the
     DECTPU SHIFT_KEY.
  Syntax
     keyword := READ_KEY
  Examples
     1.  my_key := READ_KEY;
         Stores in the variable MY_KEY the keyword for the next key entered.
     2.  The following procedure sets the SHIFT_KEY to the last (or current)
         key, reads the next key, and returns the keyname for the shifted
         key:
         PROCEDURE user_get_shift_key
            !  Keyword for key pressed after shift key
            LOCAL key_to_shift;
            SET (SHIFT_KEY, LAST_KEY);
            key_to_shift := KEY_NAME (READ_KEY, SHIFT_KEY);
            RETURN (key_to_shift);
         ENDPROCEDURE;
  Related topics
     DEFINE_KEY   KEY_NAME   LAST_KEY   LOOKUP_KEY   READ_CHAR   SHIFT_KEY