Re: combining cond and let, to replace pcase.

[Richard Stallman]

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  > Only gut feelings here, but fall thru with bindings by default and
  > multiple t may surprise users and lead to not simple to debug code.

It would be a trivial change to replace t with some keyword, for that
functionality.  Would it actually be better?  What do other s think?

Here's a more uniform version, in which each clause
exits if it contains more than one element (after the possible keyword),
and falls through otherwise.  This makes it unnecessary to redefine
what t means as a condition -- that can be written another way (see below).

(cond* 
       ;; Same as a clause in `cond',
       (CONDITION
        DO-THIS-IF-TRUE-THEN-EXIT...)

       ;; Execute FORM and ignore its value.
       (FORM)

       ;; Variables to bind, as in let
       (:bind ((x foobar) y z (foo 5) a))
       ;; Bindings continue in effect.

       ;; Extracts substructure and binds variables around the rest
       ;; of the cond*.
       (:match (`(expt ,foo ,bar) x)
        DO-THIS-IF-IT-MATCHED-THEN-EXIT...)
       ;; Bindings continue in effect.

       ;; Like above but always falls thru to next clause.
       (:match (`(expt ,foo ,bar) x))
       ;; Bindings continue in effect.
       )



To execute several expressions and not exit, use this:

       ((progn DO-THIS-UNCONDITIONALLY-AND-DONT-STOP...)


-- 
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)