#!r6rs
;; Copyright 2009 Derick Eddington.  My MIT-style license is in the file named
;; LICENSE from the original collection this file is distributed with.

(library (yuni lib ssax private define-opt)
  (export
    define-opt)
  (import
    (except (rnrs) error)
    (yuni lib ssax private error))
  
  (define error (make-errorer "(wak ssax private define-opt)"))

(define-syntax define-opt
  (syntax-rules (optional)
    ((define-opt (name . bindings) . bodies)
      (define-opt "seek-optional" bindings () ((name . bindings) . bodies)))

    ((define-opt "seek-optional" ((optional . _opt-bindings))
       (reqd ...) ((name . _bindings) . _bodies))
      (define (name reqd ... . _rest)
	(letrec-syntax
	  ((handle-opts
	     (syntax-rules ()
	       ((_ rest bodies (var init))
		 (let ((var (if (null? rest) init
			      (if (null? (cdr rest)) (car rest)
				(error "extra rest" rest)))))
		   . bodies))
	       ((_ rest bodies var) (handle-opts rest bodies (var #f)))
	       ((_ rest bodies (var init) . other-vars)
		 (let ((var (if (null? rest) init (car rest)))
		       (new-rest (if (null? rest) '() (cdr rest))))
		   (handle-opts new-rest bodies . other-vars)))
	       ((_ rest bodies var . other-vars)
		 (handle-opts rest bodies (var #f) . other-vars))
	       ((_ rest bodies)		; no optional args, unlikely
		 (let ((_ (or (null? rest) (error "extra rest" rest))))
		   . bodies)))))
	  (handle-opts _rest _bodies . _opt-bindings))))

    ((define-opt "seek-optional" (x . rest) (reqd ...) form)
      (define-opt "seek-optional" rest (reqd ... x) form))

    ((define-opt "seek-optional" not-a-pair reqd form)
      (define . form))			; No optional found, regular define

    ((define-opt name body)		; Just the definition for 'name',
      (define name body))		; for compatibilibility with define
))

)
