clisp vs me

I'm currently learning scheme (with DrScheme) at university. I can't tell how different it is from common lisp, but as far as I know, an empty list is not 0, but ().

cons is not a mutator. It doesn't change the value of anything.

Take a look at set! (i think that's clisp... I'm too used to scheme)

All mutators have a bang! at the end.

(also, unless I'm mistaken, in order to make a real list, you should be cons'ing all the elements onto a null ().

;this works quite well in scheme



(5 6 7 8 9 10 11 12 13 14 15)

Pick one:

Thanks for the help!

Now I've got another problem. I'm trying to send 'd (the literal "d") to a function that inserts it into a list. Here's what the function looks like:

(defun setnth(mylist n x)	(setq mylist		(loop for k below (length mylist) collecting 			(if (= k n)				(eval x)				(nth k mylist)			)		)	))

But when I call that function I get an error message that says "variable D has no value." What am I doing wrong now?

Can you show us the function call?

Well, going on an assumption.

I'm imagining that you're using this:

The problem appears to be (eval x) where you're saying (eval d)

Remember, with functions, the arguments are evaluated first, so the function gets d, not 'd.

I haven't actually looked at the code for logic errors, mind you.

Where should I begin.

Your indenting style is very ugly. Don't close brackets like you are writing C.

The error comes from the (eval x) command. Normally you don't need to use eval while you're learning Lisp. eval will take some Lisp code in the form of a Lisp list and execute it. If you pass your function the symbol 'd through the parameter x, (eval x) tries to return the value of the variable d. It's just as if you wrote d instead of (eval x). Since there is no binding for a variable d, the program fails.

So you should have simply written x instead of (eval x).

The other problem comes from using (setq mylist. mylist is a local variable. Even if you change its binding with setq, that change is not visible outside the function.

Here's your function that returns the new list rather than modifying the mylist parameter:



If you want to modify a list that is passed as a parameter to a function you should look into the rplaca or rplacd functions. Of course you could simply:

What Diodor said: setf

PS. Scheme is not Common Lisp. Giving someone a Scheme answer to a Common Lisp question is like giving someone a Fortran answer to a C question.

Quote:

Original post by BradDaBug Here's what I'm trying to do. I want to fill a list with values, maybe numbers from 0 to 10. So here's what I'm doing: (let mylist 0)(dotimes (count 10) (cons count mylist)) But it says that mylist has no value. I figure this is a really easy thing to fix but I can't seem to get it working.

You are not using let correctly:

(let ((mylist nil))  (dotimes (count 10)    (cons count mylist)))

However, this will return NIL since dotimes doesn't return anything.