(use-syntax (ice-9 syncase))

(define (make-source sequence . eof)
  (let ((xs (if (not (null? eof))
               eof
               (list #f))))
    (cond ((string? sequence) (append (string->list sequence) (list xs)))
          ((vector? sequence) (append (vector->list sequence) (list xs)))
          (else (append sequence (list xs))))))

(define-syntax peek
  (syntax-rules ()
    ((_ src) (if (and (= (length src) 1) (list? (car src)))
                  (caar src)
                  (car src)))))

(define-syntax next
  (syntax-rules ()
    ((_ src) (let ((char (car src)))
                (if (and (= (length src) 1) (list? (car src)))
                    (car char)
                    (begin (set! src (cdr src)) 
                           char))))))