遅延シーケンステスト

lazyseq.cl

#!/bin/sh
#|-*- mode:lisp -*-|#
#|
exec ros -Q -- $0 "$@"
|#
(progn ;;init forms
  (ros:ensure-asdf)
  ;;#+quicklisp (ql:quickload '() :silent t)
  )

(defpackage :ros.script.a.3739587226
  (:use :cl))
(in-package :ros.script.a.3739587226)

(defconstant promise-tag (gensym))

(defun promisep (p)
  (and (consp p) (eq (car p) promise-tag)))

(defun make-promise (fn)
  (list promise-tag fn nil))

(defun force (p)
  (if (promisep p)
    (if (caddr p)
      (cadr p)
      (let ((result (funcall (cadr p))))
        (setf (cadr p) result)
        (setf (caddr p) t)
        result))
    p))

(defmacro delay (proc)
  `(make-promise (lambda () ,proc)))

(defun lseq (gen)
  (delay (cons (funcall gen) (delay (lseq gen)))))

(defun make-lseq (gen)
  (labels ((kons ()
             (cons (funcall gen) (delay (kons)))))
    (delay (kons))))

(defun lcar (p)
  (car (force p)))

(defun lcdr (p)
  (force (cdr (force p))))

(defun main (&rest argv)
  (declare (ignorable argv))
  (print (lcar (make-lseq (lambda () (read-char nil nil 'EOF)))))
  (print (lcar (lcdr (make-lseq (lambda () (read-char nil nil 'EOF))))))
  (print (lcar (lcdr (lcdr (make-lseq (lambda () (read-char nil nil 'EOF)))))))
  (print (lcar (lcdr (lcdr (lcdr (make-lseq (lambda () (read-char nil nil 'EOF)))))))))
;;; vim: set ft=lisp lisp: