Tweaks

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))))
+