vendor/quickutils-package.lisp @ 884333cfb6fb v1.3.2

Detect *all* cycles during topological sort

Previously the cycle detection was limited to detecting when we hit
a currently-being-visited node during a traversal.  So something like this would
be correctly found:

    A --> B --> C
          ^     |
          |     |
          +-----+

We start at the root (A), go to B, then to C, then to B, and detect that we're
still working on B and signal the error.

But this doesn't find all cycles, because we *start* at the root nodes, and if
a cycle doesn't have any outcropping branches we'll never reach it at all.  For
example:

    A --> B
    ^     |
    |     |
    +-----+

This graph has no roots, so we incorrectly ignore the cycle.

This patch fixes the problem by keeping a count of visited nodes and and making
sure it matches the digraph's size at the end.

Fixes https://github.com/sjl/cl-digraph/issues/4

(eval-when (:compile-toplevel :load-toplevel :execute)
  (unless (find-package "DIGRAPH.QUICKUTILS")
    (defpackage "DIGRAPH.QUICKUTILS"
      (:documentation "Package that contains Quickutil utility functions.")
      (:use :cl))))

(in-package "DIGRAPH.QUICKUTILS")

;; need to define this here so sbcl will shut the hell up about it being
;; undefined when compiling quickutils.lisp.  computers are trash.
(defparameter *utilities* nil)