Hello,

I am playing a bit with Guile and proceed along

https://scheme.com/tspl4/start.html#./start:h2

In a Scheme, exercise 2.2.3o

((car (list + - * /)) 2 3)

evaluates to 5. Of course, in Common Lisp this has to be written as

(funcall (car (list (function +)
(function -)
(function *)
(function /)))
2 3)

or, using reader macros, as

(funcall (car (list #'+ #'- #'* #'/)) 2 3)

or even, but not strictly identical anymore,

(funcall (car '(+ - * /)) 2 3)

However, at one point I managed to paste an expression into the wrong
REPL, SBCL instead of Guile, and got

(list + - * /)

evaluated by SBCL as

(NIL (LIST + - * /) NIL NIL)

Oops?! Even better, when I tried this again immediately, I got

((LIST + - * /) (LIST + - * /) (NIL (LIST + - * /) NIL NIL)
((NIL (LIST + - * /) NIL NIL)))

So there seems to be some "history expansion" going on (for "*"). But
how to explain the first result with the NILs and the expression itself?

Pointers welcome!

Axel

On 2024-03-27, Axel Reichert <mail@axel-reichert.de> wrote:
> However, at one point I managed to paste an expression into the wrong
> REPL, SBCL instead of Guile, and got
>
> (list + - * /)
> evaluated by SBCL as
>
> (NIL (LIST + - * /) NIL NIL)

In the Common Lisp interactive listener (a.k.a. REPL), there is a
standard variable called - which evaluates to the form currently
being evaluated:

https://www.lispworks.com/documentation/lw50/CLHS/Body/v__.htm

There are also variables +, ++ and +++, which hold less
recent values of -.

https://www.lispworks.com/documentation/lw50/CLHS/Body/v_pl_plp.htm

There also *, ** and ***, which hold the primary value of the
three most recent REPL evaluations, and:

https://www.lispworks.com/documentation/lw50/CLHS/Body/v__stst_.htm

As well as /, // and ///, which hold the lists of all the values
of the three most recent evaluations.

https://www.lispworks.com/documentation/lw50/CLHS/Body/v_sl_sls.htm

--
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Mastodon: @Kazinator@mstdn.ca

Kaz Kylheku <433-929-6894@kylheku.com> writes:

> In the Common Lisp interactive listener (a.k.a. REPL), there is a
> standard variable called - which evaluates to the form currently
> being evaluated:
>
> https://www.lispworks.com/documentation/lw50/CLHS/Body/v__.htm

Great, all clear now. I was aware of "*" and "**" etc., but not of the
others. My search in the SBCL docs was unsuccessful. I expected this to
be an implementation thing, not part of the hyperspec.

Many thanks!

Axel