New if-let, when-let, thread-first and thread-last macros.

* lisp/emacs-lisp/subr-x.el
(internal--listify, internal--check-binding)
(internal--build-binding-value-form, internal--build-binding)
(internal--build-bindings): New functions.
(internal--thread-argument, thread-first, thread-last)
(if-let, when-let): New macros.

* test/automated/subr-x-tests.el
(subr-x-test-if-let-single-binding-expansion)
(subr-x-test-if-let-single-symbol-expansion)
(subr-x-test-if-let-nil-related-expansion)
(subr-x-test-if-let-malformed-binding, subr-x-test-if-let-true)
(subr-x-test-if-let-false, subr-x-test-if-let-bound-references)
(subr-x-test-if-let-and-lazyness-is-preserved)
(subr-x-test-when-let-body-expansion)
(subr-x-test-when-let-single-binding-expansion)
(subr-x-test-when-let-single-symbol-expansion)
(subr-x-test-when-let-nil-related-expansion)
(subr-x-test-when-let-malformed-binding)
(subr-x-test-when-let-true, subr-x-test-when-let-false)
(subr-x-test-when-let-bound-references)
(subr-x-test-when-let-and-lazyness-is-preserved)
(subr-x-test-thread-first-no-forms)
(subr-x-test-thread-first-function-names-are-threaded)
(subr-x-test-thread-first-expansion)
(subr-x-test-thread-last-no-forms)
(subr-x-test-thread-last-function-names-are-threaded)
(subr-x-test-thread-last-expansion): New tests.

1 files changed, 8 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 1fc4a218d76..85f996f8486 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -178,6 +178,14 @@ permissions set to temporary values (e.g., for creating private files).
 ** Functions `rmail-delete-forward' and `rmail-delete-backward' take an
 optional repeat-count argument.
 
+---
+** New macros `if-let' and `when-let' allow defining bindings and to
+   execute code depending whether all values are a true.
+
+---
+** New macros `thread-first' and `thread-last' allow threading a form
+   as the first or last argument of subsequent forms.
+
 
 * Changes in Emacs 24.5 on Non-Free Operating Systems