[slime-devel] Understanding sbcl source code

[Sidney Markowitz]

jcm at sdf.lonestar.org wrote, On 5/2/09 1:50 AM:
> I'm sure there's a simple answer to this question.  I'm browsing the sbcl
> source to find the lowest level implementation of CAR and I found this
> 
> (defun car (list) (car list))
> 
> So the 'real' definition of CAR must be elsewhere.  :)  Perhaps in the C
> source code?  Would someone point me to the correct location?

When the compiler encounters car it emits inline code. So try this in sbcl

 (defun foo (x) (car x))
 (disassemble #'foo)

Compare that with

 (defun bar (x) (foo x))
 (disassemble #'bar)

The former does not contain any function call, the latter will include a
call to the function object #'foo

So the purpose of (defun car (list) (car list)) is to define a function
object #'car after the compiler has already been taught how to compile
car inline.