; -*- Mode: Scheme; Syntax: Scheme; Package: bare-machine  -*-

; This is file enum.scm.

;;;; Enumerated types

; The expression
;   (define-enumeration <e-type> (<tag>*))
; will (a) define the variable <e-type> to name an enumerated type,
; and (b) define <e-type>/<tag1> ... <e-type>/<tagn> to be small
; integers.

(define-macro (define-enumeration name cases)
  `(begin (define ,name ',(list->vector cases))
	  ,@(do ((c cases (cdr c))
		 (i 0 (+ i 1))
		 (d '() (cons `(define ,(concatenate-symbol name '/ (car c))
				 ,i)
			      d)))
		((null? c) (reverse d)))))

; Break the enumerated types abstraction.
;   (enumerand->name <integer> <e-type>) => a symbol
;   (name->enumerand <symbol>  <e-type>) => an integer

(define (enumerand->name e e-type)
  (vector-ref e-type e))

(define (name->enumerand e e-type)
  (or (vector-posq e e-type)
      (error "unknown enumerand name" e)))