Re: Use the new let-opt macro in place of pcase-let in lisp-mode.el

[Stefan Monnier]

>> IOW, define a let-when-compile macro which uses progv to setup the
>> bindings and then calls `macroexpand-all' on the body.  The body's
>> `eval-when-compile' can then use those vars just fine.

> I wrote this:

> (defmacro let-when-compile (bindings &rest body)
>   "Like `let', but allows for compile time optimization.
> \n(fn BINDINGS BODY)"
>   (declare (indent 1) (debug let))
>   `(progv ',(mapcar #'car bindings)
>        ',(mapcar (lambda (x) (eval (cadr x))) bindings)
>      ,@body))

That's not what I suggest.  The `progv' should be done at
macroexpansion-time (otherwise, you're better off using `let').


        Stefan