last, butlast: become accessors, get optional arg.

* eval.c (optimize_qquote_form): Pass nil to default
new argument of butlast.
(me_whilet, me_iflet_whenlet): Likewise for last.
(eval_init): Add optional argument to registration
of last and butlast intrinsics.

* lib.c (last, butlast): Support optional numeric
argument, like in Common Lisp.

* lib.h (last, butlast): Declarations updated.

* share/txr/stdlib/place.tl (last, butlast): New
place macros.

* txr.1: Updated documentation. The description of
last is now moved into the sequence functions
section.

1 files changed, 20 insertions, 0 deletions

diff --git a/share/txr/stdlib/place.tl b/share/txr/stdlib/place.tl
index 9bad42fa..aa534e4a 100644
--- a/share/txr/stdlib/place.tl
+++ b/share/txr/stdlib/place.tl
@@ -887,3 +887,23 @@
 (define-place-macro eighth (obj) ^(ref ,obj 7))
 (define-place-macro ninth (obj) ^(ref ,obj 8))
 (define-place-macro tenth (obj) ^(ref ,obj 9))
+
+(define-place-macro last (obj : (n nil have-n))
+  (cond
+    ((and have-n (constantp n) (not (plusp n)))
+     ^(sub ,obj t t))
+    ((and have-n (constantp n))
+     ^(sub ,obj ,(- n) t))
+    (have-n
+     ^(sub ,obj (- (max ,n 0)) t))
+    (t ^(sub ,obj -1 t))))
+
+(define-place-macro butlast (obj : (n nil have-n))
+  (cond
+    ((and have-n (constantp n) (not (plusp n)))
+     obj)
+    ((and have-n (constantp n))
+     ^(sub ,obj 0 ,(- n)))
+    (have-n
+     ^(sub ,obj 0 (- (max ,n 0))))
+    (t ^(sub ,obj 0 -1))))