Enumerated Types

(defmacro define-enum (name size (&key signed 
                                       (signed-representation :twos-complement)
                                       (reader '#'read-integer)
                                       (writer '#'write-integer)
                                       (byte-order :little-endian))
                 &rest values)

Defines an enumerated type. What this does is allow LISP-BINARY to automatically map between keywords and integer values that are expected to be found in a binary file. The SIZE is in bytes.

By specifying alternative :reader and :writer functions that are compatible with read-integer and write-integer, it's also possible to use custom integer representations not built into the library.

Example:

(define-enum speed 2 ()
   slow                 ;; Implicitly 0
   light-speed          ;; Implicitly 1
   (ridiculous-speed 5) ;; Explicit value
   ludicrous-speed)     ;; Implicitly 6

Reading:

(read-binary-type 'speed stream)

Writing:

(write-binary-type 'speed 'ridiculous-speed stream)

In DEFBINARY:

(defbinary speed-and-heading ()
   (speed 'slow :type speed)
   (direction 0.0 :type double-float))

Enums can be used to specify the representation of booleans:

;; 0 for false and 1 for true
(define-enum binary-boolean 1 ()
   nil t)
;; #xff for true and #xfe for false
(define-enum weird-boolean 1 ()
   (nil #xfe)
   (t #xff))