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Brief codereview and freshman pep talk

PostPosted: Thu Jan 17, 2019 4:10 am
by babysitter
Hi everyone! Not exactly a homework again, but fits here better.

I'm a C++ programmer and on my staycation I've decided to challenge myself and do a couple of Project Euler problems and to challenge myself even more I've decided that it is the perfect time for me to realize my long-held dream and learn some lisp at last! I've read several chapters of Land of Lisp, that's all my background here. So my first question is where I can discuss things I wrote preferable in realtime (e.g. IRC or telegram), is this forum alive anyway? :D

The problem itself (it is deep in an archive so now we can discuss it freely without spoilers):
If we list all the natural numbers below 10 that are multiples of 3 or 5, we get 3, 5, 6 and 9. The sum of these multiples is 23.
Find the sum of all the multiples of 3 or 5 below 1000.


After a considerable amount of time I've came up with something like that
Code: Select all
(defun sum-multiplies-by-3-or-5 (n)
  (labels ((is-dividable-by (num divisor)
                            (zerop (mod num divisor)))
           (is-dividable-by-3-or-5 (num)
                                   (or (is-dividable-by num 3)
                                       (is-dividable-by num 5)))
           (impl (cur sum)
                 (cond ((= cur n) sum)
                       ((is-dividable-by-3-or-5 cur) (impl (1+ cur) (+ sum cur)))
                       ((impl (1+ cur) sum)))))
    (impl 3 0)))


So now I have a billion questions about how good this code is, e.g
* should I hide functions like is-dividable-by or make them global if they are generic enough?
* recursion is a more true way of doing that than a loop?
* is the pattern of doing a local function to use it recursively good?
* what is not so good in this code that you can see right away?

Thanks!

Re: Brief codereview and freshman pep talk

PostPosted: Sun Jan 20, 2019 1:44 pm
by babysitter
where I can discuss things I wrote preferable in realtime (e.g. IRC or telegram)


looks like I found a pretty cool Discord channel tho