The function 'first' in the List domain calls SPADfirst$Lisp which is
a rather clever Lisp macro
(defmacro |SPADfirst| (l)
(let ((tem (gensym)))
`(let ((,tem ,l)) (if ,tem (car ,tem) (first-error)))))
that seems to have no more measurable overhead than calling QCAR.
Perhaps someone with more Lisp experience than me can explain it?
I think probably that (NULL (NULL x)) is optimized by Lisp (at least by SBCL).
On 9 October 2017 at 19:57, oldk1331 <[email protected]> wrote:
> On Mon, Oct 9, 2017 at 9:22 PM, Bill Page <[email protected]> wrote:
>> My benchmarking shows the Lisp macros QCAR and CONSP are no 'faster'
>> than calling 'first' and 'not empty?' from the List domain. Perhaps
>> this is due to some internal optimizations in SPAD and/or SBCL? I
>> think it is best to avoid explicit Lisp dependencies if possible. Is
>> your experience different?
>>
>> Bill Page.
>
> I didn't do a benchmarking, but I know that "first" does an extra empty check,
> and "not empty?" translates to (NULL (NULL x)) and can't be inlined.
>
> The compiler should not be able to optimize them away, there should
> be a performance difference in more complicated situation.
>
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