You! Yes you, brave lisper! Lenny the lisp alien needs your help! Lenny wants to go hang out with all the other lisp aliens, but their parents have told Lenny that they're not going anywhere until their room is clean.
The issue is, Lenny can hardly see the floor! Lenny can't tell their atoms from their
conses, their symbols from their keywords, their cars from their cdrs!
Can you help Lenny sort this mess out? Don't forget your parentheses, you'll be needing them!
Before Lenny can get started, they need a refresher on what symbols and keywords
look like – it's been a while since they last tidied up... Help Lenny out by
defining two functions: lennys-favorite-food which evaluates to some symbol,
and lennys-secret-keyword which evaluates to some keyword. For example:
(lennys-favorite-food) ; => LASAGNA(lennys-secret-keyword) ; => :ALIENS-ARE-REALNote that you can return any symbol or keyword you'd like (if you're not a fan of lasagna or aren't a believer in aliens).
Once Lenny has had a refresher on symbols and keywords, it's time to get
cleaning! To sort through all of the S-Expressions laying around their room, Lenny
needs help determining what is a cons and what is an atom. You can help by
implementing two functions, is-an-atom-p and is-a-cons-p:
(is-an-atom-p 'one-thing) ; => T
(is-an-atom-p '(two things)) ; => NIL(is-a-cons-p 'one-thing) ; => NIL
(is-a-cons-p '(two things)) ; => TFor this section, there are a number of built-in lisp functions that you may
find useful. Additionally, for now, you can simply consider T as true and
NIL as false.
Finally, Lenny's conses are too bulky to put away neatly, so they need to split
them up into smaller parts. Can you help by defining two more functions to break
up their conses (first-thing and rest-of-it)?
(first-thing '(first second third)) ; => FIRST
(rest-of-it '(first second third)) ; => (SECOND THIRD)Again, some of Common Lisp's built-in functions might come in handy here.