Re: let-alias

[Helmut Eller <eller.helmut@gmail.com>]

On Wed, May 06 2020, Philipp Stephani wrote:

>> Inside BODY, wherever NEW-NAME is used as function name it should
>> produce the same result as using OLD-NAME would.  E.g.
>>
>>   (let-alias ((c car)) (c x))            ===  (car x)
>>   (let-alias ((c car)) #'c)              ===  #'car
>>   (let-alias ((c car)) (setf (c x) y))   ===  (setf (car x) y)
>>   (let-alias ((when-not unless)) (when-not x y)) === (unless x y)
>>
>> Would somebody be opposed to such a new special form? Or better yet, is
>> there already some way to achieve this?
>
>
> If you don't mind the quoting, you can use (cl-flet ((c #'car)) ...)

Hmm, didn't even know that cl-flet had this feature.  But the
bytecode for

  (defun foo (x)
    (cl-flet ((c #'car))
      (c x)))
  
is

byte code for foo:
  doc:   ...
  args: (arg1)
0	constant  car
1	dup	  
2	stack-ref 2
3	call	  1
4	return	  

while the bytecdoe for

(defun bar (x)
  (car x))

is

byte code for bar:
  doc:   ...
  args: (arg1)
0	dup	  
1	car	  
2	return	  

So it's obviously not doing what one would expect from an (zero cost)
alias.  cl-flet also doesn't seem to work for the (setf (c x) ...)
example.

Helmut