Re: Code for cond*

[Richard Stallman]

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  > Is this what you're referring to?

  >         ((get (car subpat) 'cond*-expander)
  >          ;; Treat result as a subpattern.
  >          (cond*-subpat (funcall (get (car subpat) 'cond*-expander) subpat)
  >                        cdr-safe bindings backtrack-aliases data))

  > do we have reasons to believe that it's flexible enough?

Nobody is actually using this now, so now is the best time
to make changes -- perhaps to make it somehow more flexible.
But I have no concrete idea of what flexibility you wish for.

Can you make a concrete suggestion?  Then I might understand.

  > Pcase currently doesn't support exactly this, but does support it within
  > the backquote pattern, i.e. instead of

  >     [PAT1 PAT2 ...]

  > you have to use

  >     `[,PAT1 ,PAT2 ...]

I think that's what people will actually want to use.
I meant here to imitate pcase, but I did not remember it in detail.

So I made both forms work in cond*, but maybe the latter is the only
one we really need.

  > except that in Pcase, the value is passed as the last argument rather as
  > first argument.  I haven't seen a strong reason to prefer one over the
  > other.

With the cond* syntax for simple constrained variables,
that ordering is natural.  the variable to be bound
goes in the same spot as its value will be passed to the predicate.

 (< x 15)  as a pattern means, conceptually, bind x and evaluate (< x 15).

So the question is whether to use

  (pred < x 15)

or just

  (< x 15)

I prefer the latter because it is more concise.
The equivalent (and (pred...) car) is used often in pcase
so other forms ofit will be used often also.

-- 
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)