diff options
Diffstat (limited to 'share')
| -rw-r--r-- | share/txr/stdlib/place.tl | 20 |
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)))) |