Hello all,

I am a big Lisp-Newb and am struggling with a program that is supposed to encrypt a string with Caesar's cipher. What I have in mind is a function that takes in 2 arguments: a string and a number to specify the modulus. Something along the lines:

(defun c-encrypt (string number)
("lots of helper functions"))

My thoughts so far are that it would be best to set the alphabet as a parameter and write a function that looks up a char's position in the parameter and then shifts it the wanted Caesar's modulo to the right e.g. A ->modulo 7 -> H

May look something along the lines:



Then I could take that function and mapcar it over the list of characters that are the input-string in single letters:


Well, I ran headfirst into a lot of problems. First of all, I can not find a function to split a string into its single chars (convert it to numbers fine, but simply split it...).
When trying to concatenate or looping there are always these darn #\ left which make it impossible to use the parameter.

As you see I already fail at the first obstacle of the whole project... Not to speak about the rest...

Any help would be greatly appreciated since I really start to get frustrated about this project and Lisp itself. For some reason I find it extremely difficult to "think Lisp".

Thanks already for your answers!

I'm afraid there is very little I can do for Scheme (I guess that's Scheme), but my implementation in Clojure might help you a little bit. http://github.com/Raynes/Cipher/blob/maste...pher/cipher.clj

Remember that Lisp is not a language. Lisp is a family of languages. You can't just say "I'm coding in Lisp." and expect people to know what you're talking about.

Thanks for the answer and you are of course right, I should have specified that I use Slime and Emacs (Lispbox) on a Windows machine. Anyway, by now I figured the problem out like this:

That means you're using Common Lisp. It's one of the most, probably the most popular Lisp dialect right now. If you enjoy Lisp, and want to do some serious work with it, I suggest you check out Clojure sometime. It's teh awesome. Good luck, and have fun Lisping.