repair to single-valued tracking

original commit: 8eb7644eb5def8d2a0864ef71610457d8be8c111
2019-02-02 14:12:04 -07:00 · 2019-02-02 14:12:04 -07:00 · 9974c3bf7e
commit 9974c3bf7e
parent 3db5d5ab2d
1 changed files with 3 additions and 1 deletions
--- a/s/cp0.ss
+++ b/s/cp0.ss
@ -962,7 +962,9 @@
                 (if (pair? val)
                     (car val)
                     (let ([r (pred?)])
-                       (set-cdr! a (cons r (cdr a)))
+                       (let ([p (cdr a)])
+                         (unless (pair? p)
+                           (set-cdr! a (cons r p))))
                       r)))))]))

      (define-syntax with-memoize