How can I write a MEMBER function using the DO macro in Common Lisp? -


i trying make function works member function in common lisp. so, want make function work :

(my-member 2 '(1 4 5 5 3 2 5 6 9)) => (2 5 6 9)

this same how member function works.;

(member 2 '(1 4 5 5 3 2 5 6 9)) => (2 5 6 9)

the condition should use 'do' macro make function. code have written make function :

(defun my-member (item x)   "this function works member function."   (do ((z x (rest z))                        (e (first x) (first z)))       (:when (equal item (first z))                    (return z))))

but doesn't work..

(my-member 2 '(3 4 5 2 1 1)) -> (3 4 5 2 1 1)

what should solve problem?

here correct way use do:

(do ((var 0 (1+ var))      (lst '() (cons var lst)))     ((= var 5) lst))) ; ==> (4 3 2 1 0)

so both var , lst variables initialised 0 , () , after each iteration variable set (1+ var) , (cons var lst).

what determines when should stop (= var 5) becoming not nil , when happens result of whole do form lst. second part of do , last has since not supply body.

you can make equivalent of member function using 1 variable , second part end condition , should result of do. luck!


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