Question

Note Learning Lisp

I am getting this error:

Illegal argument in functor position: (EVALEXP (CDR MAIN-LIST) BIND-LIST) 
in ((EVALEXP(CDR   MAIN-LIST) BIND-LIST))

from this:

(defun evalexp (main-list bind-list)

(if (eq nil (cdr main-list)) 
    (  (if  (eq nil  (atom (car main-list))) (evalexp (car main-list) bind-list) ) )

( (print (car main-list))
  (evalexp (cdr main-list) bind-list) )
)

main-list contains this list:

(and 1 (or a b))

What is in bind-list doesn’t matter because I am not using it yet. I am trying to loop through the list printing out each car. Any ideas why I am getting this error?

Answer 1

Extra parentheses.

Normally the first thing after an opening parenthesis is a function name. You have another opening parenthesis there in some cases, which is a syntax error, as you saw.

You also seem to want a statement block. progn often fits the bill. You could use a block for the inner if, but it’s really not necessary since it would contain only one statement.

(defun evalexp (main-list bind-list)
  (if (eq nil (cdr main-list)) 
      (if  (eq nil (atom (car main-list))) (evalexp (car main-list) bind-list) )
      (progn
        (print (car main-list))
        (evalexp (cdr main-list) bind-list) )
  )
)