(defun copy-seq (sequence)
(subseq sequence 0))
+
+
+;;; Reduce (based on SBCL's version)
+
+(defun reduce (function sequence &key key from-end (start 0) end (initial-value nil ivp))
+ (let ((key (or key #'identity))
+ (end (or end (length sequence))))
+ (if (= end start)
+ (if ivp initial-value (funcall function))
+ (macrolet ((reduce-list (function sequence key start end initial-value ivp from-end)
+ `(let ((sequence
+ ,(if from-end
+ `(reverse (nthcdr ,start ,sequence))
+ `(nthcdr ,start ,sequence))))
+ (do ((count (if ,ivp ,start (1+ ,start))
+ (1+ count))
+ (sequence (if ,ivp sequence (cdr sequence))
+ (cdr sequence))
+ (value (if ,ivp ,initial-value (funcall ,key (car sequence)))
+ ,(if from-end
+ `(funcall ,function (funcall ,key (car sequence)) value)
+ `(funcall ,function value (funcall ,key (car sequence))))))
+ ((>= count ,end) value)))))
+ (if from-end
+ (reduce-list function sequence key start end initial-value ivp t)
+ (reduce-list function sequence key start end initial-value ivp nil))))))
(test (equal (subseq nums 2 4) '(3 4)))
; Test that nums hasn't been altered: SUBSEQ should construct fresh lists
(test (equal nums '(1 2 3 4 5))))
+
+;;; REDUCE
+(test (equal (reduce (lambda (x y) `(+ ,x ,y))
+ '(1 2 3 4))
+ '(+ (+ (+ 1 2) 3) 4)))
+
+(test (equal (reduce (lambda (x y) `(+ ,x ,y))
+ '(1 2 3 4)
+ :from-end t)
+ '(+ 1 (+ 2 (+ 3 4)))))
+
+(test (equal (reduce #'+ nil) 0))
+(test (equal (reduce #'+ '(1)) 1))
+(test (equal (reduce #'+ nil :initial-value 1) 1))
+
+(test (equal (reduce #'+ '()
+ :key #'1+
+ :initial-value 100)
+ 100))
+
+(test (equal (reduce #'+ '(100) :key #'1+)
+ 101))