exercises and notes from "Gentle introduction"

assignment.lisp

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+
+(setf circ (list 'foo))
+(setf (cdr circ) circ)
+
+circ
+
+;;;  setf modifies "pointers"
+;;;  and getter returns a reference
+;;;  so using setf with getter as "place" works as a setter
+;;;
+;;; append - nondestructive
+;;; nconc - destructive merging of lists
+
+(nconc '(hello lists) '("and" "with" other 15 "values"))
+
+;; subst - nondesctructive
+;; nsubst - destructive
+
+(setf tree '(i say (e i (e i) o)))
+(subst 'a 'e tree)
+tree
+
+(nsubst 'a 'e tree)
+(nsubst 'cherry '(a i) tree :test #'equal)
+;; this modifies the list
+
+;;; exercise,
+;; chop - redule non nil list to list of head
+(defun chop (x)
+  (setf (cdr x) nil))
+
+(setf my-list '(1 2 "hello"))
+(chop my-list)
+my-list
+
+(defun ntack (x a)
+  (setf (cdr (last x)) (list a)))
+(setf my-test-ntack-list '(1 2 "hello"))
+(ntack my-test-ntack-list 'boo)
+my-test-ntack-list
+
+;; and more recursion
+(setf h '(hi ho))
+(setf (cdr (last h)) h)
+
+;;; setq - before "generalized variables", only sets value of ordinary variables
+(setq x '(slings and arrows))
+(setq (cdr x) (list "hello"))           ; variable name is not a symbol