;; Stream processing

(module stream mzscheme


  ;; Lazy list

  
  ;; Wadler's recipe:
  
  ;; * wrap all constructors (e.g., '(), cons) with delay,
  ;; * apply force to arguments of deconstructors (e.g., car, cdr and null?),
  ;; * wrap procedure bodies with (delay (force ...)).

  ;; All names prefixed with '@' operate on lazy lists.
  
  (define-syntax @cons
    (syntax-rules ()
      ((_ a b) (delay (cons a b)))))

  (define @nil (delay '()))
  
  (define (@car c)    (car (force c)))
  (define (@cdr c)    (cdr (force c)))
  (define (@null? c)  (null? (force c)))

  ;; Universal list iteration.
  
  (define (@fold f v l)
    (if (@null? l)
        (delay v)
        (delay
          (f (@car l)
             (force
              (@fold f v (@cdr l)))))))
     
     
    

            
  ;; Matcher


  )