Re: Code for cond*

[Madhu <enometh@meer.net>]

* JD Smith <1AD5807F-91F7-4B92-BCB0-D0FEA904A75D @gmail.com> :
Wrote on Tue, 23 Jan 2024 23:49:06 -0500:

> In general I’ve always felt cond by itself was missing some
> functionality and could really use the ability to make bindings — a
> cond-let if you will.

[Using an example from another thread]

```
  (t (let ((temp (cadr whatsis)))
       (cond ((eq temp 'foo))
             ...
```

The idiom i've seen from 80s code is to explicitly pull the bindings to
the outermost scope (like cl loop  does when expanded)

```
(let (temp)
  (cond ((eq (setq temp (cadr whatsis)) 'foo))
   ...
```

This solves one indentation problem and creates another.

>  Even making and testing bindings local to each
> cond clause would be a real advance[1].  Pattern matching adds another
> level of complexity I hadn’t considered, but overall I'm supportive of
> efforts to improve cond.

[...]

> [1] I regularly convince myself that it’s such low hanging fruit, there must in fact already BE a cond-let, and I go hunting for it.  The obvious interface seems like such a straightforward extension of if/when-let, that there would be absolutely nothing new to learn:
>
> (cond-let
>  (((var value)
>    (dvar (derived-from var))
>    ((has-the-right-stuff-p dvar)))
>   (cons 'correct dvar))
>
>  (((foo value2)
>    (bar (1- foo))
>    ((< bar 0)))
>   (cons 'incorrect bar))
>
>  (t nil))