* lib.c (car, cdr): Semantics fix for lazy conses.

Ignore the return value of the lazy cons function: do not
return nil if the function returns nil.
This useless behavior was a source of inconvenience in lazy
cons programming, requiring the lazy function to return
non-nil in addition to installing the car and cdr fields.

1 files changed, 2 insertions, 4 deletions

diff --git a/lib.c b/lib.c
index 64cf66eb..575465e7 100644
--- a/lib.c
+++ b/lib.c
@@ -183,8 +183,7 @@ val car(val cons)
     if (cons->lc.func == nil) {
       return cons->lc.car;
     } else {
-      if (!funcall1(cons->lc.func, cons))
-        return nil;
+      funcall1(cons->lc.func, cons);
       return cons->lc.car;
     }
   default:
@@ -203,8 +202,7 @@ val cdr(val cons)
     if (cons->lc.func == nil) {
       return cons->lc.cdr;
     } else {
-      if (!funcall1(cons->lc.func, cons))
-        return nil;
+      funcall1(cons->lc.func, cons);
       return cons->lc.cdr;
     }
   default: