On Sat, Dec 7, 2019 at 5:48 AM Richard Stallman <rms@gnu.org> wrote:

> What does Common Lisp say about the return value of 'push'?

From the Common Lisp Hyperspec:


*Macro* *PUSH*

*Syntax:*

*push* *item place* => *new-place-value*

*Arguments and Values:*

*item*---an *object* <26_glo_o.htm#object>.

*place*---a *place* <26_glo_p.htm#place>, the *value* <26_glo_v.htm#value> of
which may be any *object* <26_glo_o.htm#object>.

*new-place-value*---a *list* <26_glo_l.htm#list> (the new *value*
<26_glo_v.htm#value> of *place*).

*Description:*

*push* <#push> prepends *item* to the *list* <26_glo_l.htm#list> that is
stored in *place*, stores the resulting *list* <26_glo_l.htm#list> in
*place*, and returns the *list* <26_glo_l.htm#list>.


> If Common Lisp describes a certain return value for 'push',
> people will tend to use it that way,

Yes, though as I said, it is very rarely used, at least on our sources. 34
uses
out of ~4,100.

There are also a lot like

(and test-1
     test-2
     ...
     (push item place))

but don't really depend on the return value of `push', they're just using
`and'
as a conditional.

> and I think it would be
> a waste of time changing all code that ever depends on that return value.

At least for our sources, that time's already been wasted, whether we apply
my
patch or not.

> It would be easier to document that return value.

I tend to agree, because I don't like gratuitously discarding CL
compatibility.