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authorColin Okay <colin@cicadas.surf>2022-10-23 10:26:57 -0500
committerColin Okay <colin@cicadas.surf>2022-10-23 10:26:57 -0500
commitbc21ac80e5b3b1449a7c7b7df36fc2d48d9ba355 (patch)
treef8b13f0025ff0ea4465ad3f6ad9f4ea302ae88a2
parent15cbf6b594e81fddc5ad4666789855f85faf741b (diff)
Tweaks
-rw-r--r--utilities.lisp35
1 files changed, 22 insertions, 13 deletions
diff --git a/utilities.lisp b/utilities.lisp
index 69ddcfe..525e2c1 100644
--- a/utilities.lisp
+++ b/utilities.lisp
@@ -13,7 +13,7 @@
host
(get-universal-time))))))
-(defun take (n list &key share-tail)
+(defun take (n list &optional share-tail)
"Returns two values. The first value returned is a list of the first
N members of LIST. The second value is a list of the remaining
values of list.
@@ -34,20 +34,35 @@
tail
(copy-seq tail)))))))
-(defun insert-nth (x n list)
+(defun insert-nth (x n list &optional share-tail)
"Creates a new list, the result of inserting X into the Nth position
of LIST, displacing the rest of the elements by one position. If N
is greater than the length of LIST, X becomes the last element of
- LIST. If N is negative, the element is inserted from the back of
+ LIST.
+
+ If N is negative, the element is inserted from the back of
the list. If the abslute value of -N is greater than the lenght of
the list, a list just containing X is returned."
(when (minusp n)
(setf n (+ 1 n (length list))))
- (multiple-value-bind (front back) (take n list)
- ;; NCONC ok b/c this call to TAKE returns values that do not shre
- ;; memory with LIST
+ (multiple-value-bind (front back) (take n list share-tail)
(nconc front (cons x back))))
+(defun remove-nth (n list &optional share-tail)
+ "Removes Nth member of list. Returns two values.
+
+ The first value is the new list with the Nth member removed. The
+ second value is the removed item.
+
+ See insert-nth for a description of the behavior of negative values
+ of N, and for documentation on SHARE-TAIL."
+ (when (minusp n)
+ (setf n (+ n (length list))))
+ (multiple-value-bind (front back) (take n list share-tail)
+ (values
+ (nconc front (cdr back))
+ (car back))))
+
(defun nswap (list n m)
"Swap Nth and Mth members of LIST. Mutates LIST. Assumes both N and
M are less than the length of LIST."
@@ -56,10 +71,4 @@
(nth m list) tmp)
list))
-(defun pop-nth (n list &optional share-tail)
- (when (minusp n)
- (setf n (+ n (length list))))
- (multiple-value-bind (front back) (take n list share-tail)
- (values
- (nconc front (cdr back))
- (car back))))
+