# HG changeset patch
# User Steve Losh <steve@stevelosh.com>
# Date 1459020609 0
# Node ID a9bdea1a95644b9729e10dd128c3b5e5d4b0cf9c
# Parent  d4ba6547d8a1dd692becf4fc58c6c1b6cc9e4e50
Clean up topological-sort

We don't actually need to get the full set of minimal elements on each iteration
because we don't need to break ties.  It'll be faster (and cleaner) to just grab
the first one we find.

diff -r d4ba6547d8a1 -r a9bdea1a9564 src/wam/topological-sort.lisp
--- a/src/wam/topological-sort.lisp	Sat Mar 26 19:21:05 2016 +0000
+++ b/src/wam/topological-sort.lisp	Sat Mar 26 19:30:09 2016 +0000
@@ -20,30 +20,28 @@
 
   "
   (labels
-      ((find-minimal-elements (elements constraints)
-         ;; An element is minimal if there are no other elements that are
-         ;; required to precede it.
-         (remove-if #'(lambda (element)
-                       (member (funcall key element)
-                               constraints
-                               :key #'cdr
-                               :test key-test))
-                    elements))
+      ((minimal-p (element constraints)
+         ;; An element is minimal if there are no other elements that must
+         ;; precede it.
+         (not (member (funcall key element) constraints
+                      :key #'cdr
+                      :test key-test)))
        (in-constraint (val constraint)
          ;; Return whether val is either part of a constraint.
          (or (funcall key-test val (car constraint))
              (funcall key-test val (cdr constraint))))
        (recur (remaining-constraints remaining-elements result)
-         (let ((minimal-elements (find-minimal-elements remaining-elements
-                                                        remaining-constraints)))
-           (if (null minimal-elements)
+         (let ((minimal-element
+                 (find-if #'(lambda (el)
+                             (minimal-p el remaining-constraints))
+                          remaining-elements)))
+           (if (null minimal-element)
              (if (null remaining-elements)
                result
                (error "Inconsistent constraints."))
-             (let ((choice (car minimal-elements)))
-               (recur (remove (funcall key choice)
-                              remaining-constraints
-                              :test #'in-constraint)
-                      (remove choice remaining-elements :test test)
-                      (cons choice result)))))))
+             (recur (remove (funcall key minimal-element)
+                            remaining-constraints
+                            :test #'in-constraint)
+                    (remove minimal-element remaining-elements :test test)
+                    (cons minimal-element result))))))
     (reverse (recur constraints elements (list)))))