GNU bug report logs - #76413
[PATCH] New macro 'compf' for composing functions

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Eshel Yaron <me <at> eshelyaron.com>
To: bug-gnu-emacs <at> gnu.org
Subject: [PATCH] New macro 'compf' for composing functions
Date: Wed, 19 Feb 2025 14:52:11 +0100

[Message part 1 (text/plain, inline)]

Tags: patch

This patch adds a new macro 'compf' that streamlines the common pattern
of function composition.

Namely, instead of (lambda (x) (foo (bar (baz x)))), with this macro we
can write (compf foo bar baz), which expands to exactly the same form.

This is similar in essence to the "compose" function proposed in
https://lists.gnu.org/archive/html/emacs-devel/2021-02/msg01138.html
with the main difference that compf is a macro, not a function, so it
incurs no runtime performance penalty.

There are many occurrences of function composition in the Emacs code
base alone that can be simplified with this macro.  For example:

- In lisp/calc/calc-mode.el:
  (lambda (v) (symbol-value (car v)))       => (compf symbol-value car)
- In lisp/dired-aux.el:
  (lambda (dir) (not (file-remote-p dir)))  => (compf not file-remote-p)
- In lisp/env.el:
  (lambda (var) (getenv (upcase var)))      => (compf getenv upcase)
- In lisp/mail/smtpmail.el:
  (lambda (s) (intern (downcase s)))        => (compf intern downcase)
- In lisp/net/tramp-container.el:
  (lambda (line) (car (split-string line))) => (compf car split-line)
- ...


Best,

Eshel

[0001-New-macro-compf-for-composing-functions.patch (text/patch, attachment)]

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