## Solved- append a new atom upon finding specific atom

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prashu421
Posts: 1
Joined: Sat Jan 06, 2018 11:39 pm

### Solved- append a new atom upon finding specific atom

I've recently started working on LISP as part of my course.
I am trying to add a new atom after every search atom in the list, my code is as below -

Code: Select all

``````(defun appendConst (OLD NEW L)
(cond
((null L) ())
((EQ (car L) OLD) (cons OLD (cons NEW (cdr L))))
(T (cons (car L) (appendConst OLD NEW (cdr L))))
))``````
This is working fine, but only adding the required atom in first occurrence. Please check example below -
Input: (appendConst 'a 'd '(a c e a m k))
Ouput: (A D C E A M K)
Required Output: (A D C E A D M K)

I tried calling the function recursively, but I can see that it doesn't work, as the no. of arguments are not properly being passed.

Code: Select all

``````(defun appendConst (OLD NEW L)
(cond
((null L) ())
((EQ (car L) OLD) (appendConst (cons OLD (cons NEW (cdr L))))  )
(T (cons (car L) (appendConst OLD NEW (cdr L))))
))``````
Thanks.

David Mullen
Posts: 78
Joined: Mon Dec 01, 2014 12:29 pm
Contact:

### Re: Solved- append a new atom upon finding specific atom

You're closeâ€”it just wants to be flipped inside out a little bitâ€”the second clause should be like this:

Code: Select all

``((EQ (car L) OLD) (cons OLD (cons NEW (appendConst OLD NEW (cdr L)))))``