Why won't this little Lisp expression work? [closed]

Question

Closed. This question needs details or clarity. It is not currently accepting answers.

---

Want to improve this question? Add details and clarify the problem by editing this post.

Closed 8 years ago.

Improve this question

This is day 1 of Lisp for me. I am trying to eventually write an if else statement...hopefully sometime this year. I am not sure why this is giving me an error?

(cond (< 1 2) (print "hey"))

Why is this crashing? It says the variable '<' is unbound? I don't get Lisp at all... Thanks in advance.

Answer 1

cond takes a list of tests and clauses

(cond (<test>  <if test is true>)
      (<test2> <if test2 is true>)
      ...)

I think what you meant to write is

(cond ((< 1 2) (print "hey"))) ;; if 1 is less than 2, print "hey"

What you've actually got in your question is

(cond (< 1 2)        ;; if `<` is bound as a variable, return 2
      (print "hey")) ;; if `print` is bound as a variable, return "hey"

Neither of those symbols are defined in the variable namespace by default, so you'll get an error.

If you only have one form to dispatch on, and only want to do something if it's true, it's more common to use when than cond.

(when (< 1 2) (print "hey"))