Re: Anaphoric macros: increase visibility

[Tino Calancha <tino.calancha@gmail.com>]

On Fri, 13 Jan 2017, Michael Heerdegen wrote:

> Tino Calancha <tino.calancha@gmail.com> writes:
>
>> Hi,
>>
>> I think anaphoric macros are a nice idiom; occasionally
>> they allow to write very concise and clear expressions.
>>
>> AFAICS, in the Emacs tree they are just introduced in ibuf-macs.el
>> (`ibuffer-aif', `ibuffer-awhen').
>
> We also already have `if-let' and `when-let' in "subr-x".  They are like
> `aif' and `awhen' but you specify "it" explicitly.
They looks also fun.  Thanks.
I wonder if it has sense to increase that family with a while-let
(maybe others in case they are useful).

From 60f26b512b191add12a0c91dc4d7ff95aba080d9 Mon Sep 17 00:00:00 2001
From: Tino Calancha <tino.calancha@gmail.com>
Date: Sat, 14 Jan 2017 14:25:42 +0900
Subject: [PATCH] * lisp/emacs-lisp/subr-x.el (while-let): New macro.

---
  lisp/emacs-lisp/subr-x.el | 9 +++++++++
  1 file changed, 9 insertions(+)

diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 7736225b5f..5e7fdfaa09 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -141,6 +141,15 @@ when-let
    (declare (indent 1) (debug if-let))
    (list 'if-let bindings (macroexp-progn body)))

+(defmacro while-let (bindings &rest body)
+  "Process BINDINGS and eval BODY while all values are non-nil.
+Argument BINDINGS is a list of tuples whose car is a symbol to be
+bound and (optionally) used in BODY, and its cadr is a sexp to be
+evalled to set symbol's value.  In the special case you only want
+to bind a single value, BINDINGS can just be a plain tuple."
+  (declare (indent 1) (debug t))
+  `(while (when-let ,bindings (prog1 t ,@body))))
+
  (defsubst hash-table-empty-p (hash-table)
    "Check whether HASH-TABLE is empty (has 0 elements)."
    (zerop (hash-table-count hash-table)))
-- 
2.11.0