Re: [PATCH] Clojure-like syntactic sugar for an anonymous function literal

[David Kastrup <dak@gnu.org>]

Oleh <ohwoeowho@gmail.com> writes:

>>  > The most popular library in MELPA, https://github.com/magnars/dash.el,
>>  > implements it (for a long time) like this:
>>  >
>>  >     (--map (* it it) '(1 2 3))
>>  >     ;; => (1 4 9)
>>  >
>>  > With my approach, it's:
>>  >
>>  >     (mapcar #(* % %) '(1 2 3))
>>  >     ;; => (1 4 9)
>>
>> That looks almost like Perl!  Now I'm -2.  Just require dash.
>
> How is `dash' better? `--map' is a macro:
>
>     (defmacro --map (form list)
>       "Anaphoric form of `-map'."
>       (declare (debug (form form)))
>       `(mapcar (lambda (it) ,form) ,list))
>
> `dash' also gives other ~40 macros that look like this, littered all
> over the code in the MELPA, so it's impossible to go on without
> understanding what `dash' does.
>
> On the other hand, `mapcar' is a C function. It and all other
> functions can use `short-lambda' instead of being reimplemented as
> macros on a case-per-case basis by `dash'.

So use cl-loop.  Has the advantage of being _both_ concise as well as
efficient after compilation since Emacs Lisp is not really fast at
function calls.

(cl-loop for i from 1 to 3 collect (* i i))

Or (cl-loop for i in '(1 2 3) collect (* i i))

The code cl-loop creates is usually quite faster than any of the map*
functions.  I haven't checked with lexical bindings though: it is
conceivable that the anonymous lambda cost goes down for them, but so
does the variable-binding cost for cl-loop.

-- 
David Kastrup