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Re: Sweeter Emacs Lisp

From: Stefan Monnier
Subject: Re: Sweeter Emacs Lisp
Date: Mon, 22 Jul 2013 11:24:13 -0400
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3.50 (gnu/linux) 
>   + The *threading* macros "->" and "->>":

Feel free to contribute such macros.  I probably wouldn't want to call
them "->" and "->>".  The name should probably include "thread" or
"pipe".  To make them useful, they should come with good edebug
support, which may turn out to be the more tricky part.

>   + when-let, if-let:

As mentioned, `pcase' comes pretty close to `if-let', so I don't feel
a strong need for it.  OTOH for when-let you'd need something like

   (pcase <test>
     (`(and (pred identity) ,<binding-form>) <body>))

which is uglier.  So maybe a when-let makes sense, tho I'd prefer a when-let*
(which has also been seen under the name let-and, IIRC).

>   + *we need a built-in core mapcan (could be called mapcat), filter and
>   sequence concatenation (could be called cat?) function that doesn't
>   depends on cl-lib*. This is fundamental stuff isn't it? Why is such a
>   need to require a library for it?

The whole point of the big rename and partial rewrite of CL into cl-lib
was so that these functions can be used anywhere, thus making it
unnecessary to duplicate them into "core" Elisp.

>   + Destructuring in defun and let: This looks weirder than I thought
>   because of our (ab)use of parens everywhere, but I feel this is
>   something brillant to have as part of the core language.

For destructuring let we have pcase-let.  I have some tentative
pcase-lambda but haven't come up with something good enough yet.
I'm definitely open to suggestions here.  As for including it directly
into "core" `defun', and `let', there are some technical issues (mostly
linked to bootstrapping and the performance cost especially in
interpreted code), but I do want to make pcase patterns more generally
available (e.g. making dolist work like pcase-dolist).


        Stefan
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