src/code/late-extensions.lisp

   1 ;;;; various extensions (including SB-INT "internal extensions")
   2 ;;;; available both in the cross-compilation host Lisp and in the
   3 ;;;; target SBCL, but which can't be defined on the target until until
   4 ;;;; some significant amount of machinery (e.g. error-handling) is
   5 ;;;; defined
   6
   7 ;;;; This software is part of the SBCL system. See the README file for
   8 ;;;; more information.
   9 ;;;;
  10 ;;;; This software is derived from the CMU CL system, which was
  11 ;;;; written at Carnegie Mellon University and released into the
  12 ;;;; public domain. The software is in the public domain and is
  13 ;;;; provided with absolutely no warranty. See the COPYING and CREDITS
  14 ;;;; files for more information.
  15
  16 (in-package "SB!IMPL")
  17
  18 ;;; Is X a list for which LENGTH is meaningful, i.e. a list which is
  19 ;;; not improper and which is not circular?
  20 (defun list-with-length-p (x)
  21   (values (ignore-errors (list-length x))))
  22
  23 ;;; not used in 0.7.8, but possibly useful for defensive programming
  24 ;;; in e.g. (COERCE ... 'VECTOR)
  25 ;;;(defun list-length-or-die (x)
  26 ;;;  (or (list-length x)
  27 ;;;      ;; not clear how to do this best:
  28 ;;;      ;;   * Should this be a TYPE-ERROR? Colloquially that'd make
  29 ;;;      ;;     lots of sense, but since I'm not sure how to express
  30 ;;;      ;;     "noncircular list" as a Lisp type expression, coding
  31 ;;;      ;;     it seems awkward.
  32 ;;;      ;;   * Should the ERROR object include the offending value?
  33 ;;;      ;;     Ordinarily that's helpful, but if the user doesn't have
  34 ;;;      ;;     his printer set up to deal with cyclicity, we might not
  35 ;;;      ;;     be doing him a favor by printing the object here.
  36 ;;;      ;; -- WHN 2002-10-19
  37 ;;;      (error "can't calculate length of cyclic list")))