Unbound Variable on Function Name

I'm writing a program in Lisp(common lisp dialect).. I want the program to count the number of sublists in a list.. This is what I have written till now:

(defun llength (L)
      (cond 
          ((null L)   0)    
          ((list (first L)) (progn (+ (llength (first L)) 1) (llength (rest L))))    
          ((atom (first 开发者_开发技巧L)) (llength (rest L)))
      )
)

The function returns the error "Unbound variable: LLENGTH" and I don't understand why or how I can fix it.. Any suggestions ?

You have multiple errors in your code.

First of all, list function creates new list, not checking if it is a list. The function you need is listp - "p" at the end means "predicate".

Second, (progn (+ (llength (first L)) 1) (llength (rest L)) will not increase counter. progn performs expressions one by one and returns result of the last expression, other results are just thrown out. progn is there mostly for side effects. What you actually need is addition of all three components: 1 to indicate one found list, result of applying function to the first element and result for applying to the rest. So, this line must be:

((listp (first L)) (+ (llength (first L)) (llength (rest L)) 1))

More errors may exist, please, be careful to indent code correctly - it really helps to reduce them.

When you define a function with the (defun function name (parameters)) call you must then call the function by typing:

(function name (parameters))

Perhaps you were simply typing:

function name (parameters)

Doing this will get you the error you are receiving so be sure to encompass your whole statement in parenthesis.

(defun llength (list)
  (cond 
    ((null list) 0)
    ((listp (first list))
     ;; 1 + the count of any sub-lists in this sub-list + the 
     ;; count of any sub-lists in the rest of the list.
     (+ 1 (llength (first list))
        (llength (rest list))))
    (t (llength (rest list)))))

Test:

> (llength '(1 2 3 4))
0
> (llength '(1 2 (3 4)))
1
> (llength '(1 2 (3 (4))))
2
> (llength '(1 2 (3 4) (5 6) (7 8) (9 (10 (11)))))
6