zerop | Zero Punctuation episodes

omg I feel stupid.

I think your problem is caused by the redeclaration of i in the second for loop

The CL printer is a complicated and wonderful thing, and I've forgotten most of the little I used to know about it, so this answer may well be wrong.

There is no trivial way to control the printing of large strings: you can control the printing of large general arrays with *print-array*, but there is a special exception for strings in that.

There is then a bad approach and a less-bad approach.

The bad approach: define a method on print-object. I think you are allowed to do this for strings, but if you do this then your method will be called whenever you want a string to be printed, so you had better be sure it is right. Probably the way of ensuring that is to make sure that it listens to some variable and, unless the variable asks it to do something it just uses call-next-method to punt to an implementation which probably is right.

The less-bad approach: use the pretty printer's dispatch table to do what you need. This is less-bad (and perhaps even good) because it won't alter what happens when *print-pretty* is false and you also can simply put back the original table whenever you want to.

Here is a toy attempt to do this. Warning: I have not spent enough time to think hard enough about how this interacts with all the printer control settings, and as I said I have forgotten a lot of the details, so it is almost certainly simply incorrect in many cases. So, don't use this in production code, but something like it might be adequate for debugging purposes, where what gets printed just has to tell you enough to debug the program & need not be correct in every detail.

I am not sure if there is any special bit logic function, see e.g. here.

But how about this?

Emacs tries to lazy load (called autoloading) some of its features. math-zerop is defined as part of the calc-misc feature (in calc-misc.el).

You can load it by (require 'calc) which loads the calc-misc feature.

You hanve the case where the list is empty and when you actually find a multiple of 3, but what happens if it is a nother number you should skip? You have do default term so Common Lisp will return nil. Eg your code works like this:

Without knowing too much about how you think its supposed to work you need to define tape, pointer and output as global variables, preferrably with *earmuffs* so that you can see they are globals.

You're making things more complex than necessary with the first loop... just collect the parameters instead

One possible solution would be to use the LOOP macro of Common Lisp, e.g.: