[Openmcl-devel] Loop in function that should fail with type error

[Ron Garret]

It’s a compiler optimization.  This code:

>   (if (eq nil l) 
>       l 
>      (- (car (cdr l)) (car l)))

doesn’t change any state and the result is immediately discarded, so it’s dead code.

You can “fix” this by doing something with the value returned by that code snippet, e.g.:

(defun wrong(l)
    (setf *value* (if (eq nil l) 
                    l 
                    (- (car (cdr l)) (car l))))
    (wrong (cdr l)))

rg

On Jul 9, 2015, at 3:33 PM, Renzo Orsini <orsini at unive.it> wrote:

> The following (absurd) function:
> 
> (defun wrong(l)
>   (if (eq nil l) 
>       l 
>      (- (car (cdr l)) (car l)))
>  (wrong (cdr l)))
> 
> if called as in: (wrong ‘(10 5)) should terminate with an error due to the application of the operator “-“ to NIL (this for instance happen in SBCL). But when I try it in CCL it seems to enter in an infinite loop. Is this an error? Some effect of the compiler optimization?
> 
> Should I open a ticket?
> 
> Thanks,
> 
> Renzo
> 
> 
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