diff options
| -rw-r--r-- | gtwiwtg.lisp | 40 | ||||
| -rw-r--r-- | package.lisp | 2 |
2 files changed, 41 insertions, 1 deletions
diff --git a/gtwiwtg.lisp b/gtwiwtg.lisp index 76bcc60..a0e74e7 100644 --- a/gtwiwtg.lisp +++ b/gtwiwtg.lisp @@ -318,6 +318,28 @@ Example: "Consumes GEN by collecting its values into a list." (nreverse (fold (xs nil) (x gen) (cons x xs)))) +(defun take (n gen) + "Consumes GEN by collecting its first N values into a list" + (nreverse (fold (xs nil) (x (zip! gen (times (1- n)))) + (cons (car x) xs)))) + +(defun pick-out (indexes gen) + "Consumes GEN by picking out certain members by their index. + +INDEXES is a list of non-negative integers. + +Returns a list of values from GEN such that each value was an element +of indexes." + (let ((acc (make-array (length indexes)))) + (iter ((x idx) (zip! gen (times (apply #'max indexes)))) + (when (member idx indexes) + (loop + :for i :below (length indexes) + :for idx2 :in indexes + :when (= idx2 idx) + :do (setf (aref acc i) x)))) + (concatenate 'list acc))) + (defun size (gen) "Consumes GEN by calculating its size." (fold (n 0) (x gen) (1+ n))) @@ -362,7 +384,10 @@ is minimal among the values of GEN. VALUE is the value of (FUNCALL FN X)" am)))) -;;; example +;;; EXAMPLES + + +;; permutations (defun fill-and-insert (idx elem vec buffer) "A Utility function that inserts ELEM at IDX into BUFFER. For every @@ -394,3 +419,16 @@ Not meant for general use. just a utility used by THREAD-THROUGH" :displaced-index-offset 1 :element-type (array-element-type vec))))) (inflate! (lambda (subperm) (thread-through elem subperm)) subperms)))) + + +;; primes + +(defun prime-p (n) + (loop + :for x :from 2 :upto (sqrt n) + :when (zerop (mod n x)) :do (return nil) + :finally (return t))) + +(defun all-primes () + (filter! #'prime-p (range :from 1))) + diff --git a/package.lisp b/package.lisp index 0b8f4bf..6f853bd 100644 --- a/package.lisp +++ b/package.lisp @@ -15,6 +15,8 @@ #:iter #:fold #:collect + #:take + #:pick-out #:size #:maximum #:minimum |