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;;;; utilities.lisp
(in-package #:vampire)
(let ((host (uiop:hostname))
(count 0))
(defun nuid ()
"Generates a Nearly Universal ID"
(format nil "~36r"
(sxhash
(list
(incf count)
host
(get-universal-time))))))
(defun take (n list &key 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.
If N is negative, NIL is returned for both values. If N is greater
than the length of LIST then the entire list is returned.
If SHARE-TAIL is non-nil, the second value will
share memory with LIST, otherwise a copy is returned."
(if (zerop n)
(values nil (if share-tail list (copy-seq list)))
(loop repeat n
for (h . tail) on list
collect h into front
finally
(return (values front
(if share-tail
tail
(copy-seq tail)))))))
(defun insert-nth (x n list)
"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
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
(nconc front (cons x 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."
(let ((tmp (nth n list)))
(setf (nth n list) (nth m list)
(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))))
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