Hi, I've added two functions in `subr-x`, `while-let` and `while-let*`. `(while-let SPEC BODY)` evaluate each binding in turn and stop if a binding value is nil. BODY is evaluated repeatedly until a binding value is nil. `(while-let* VARLIST BODY)` is like `while-let` except VARLIST is of the form ((SYMBOL SOMETHING) ...). Example: Suppose we've a list, (setq xs '(1 2 3 4 5)), the following while-let form (while-let ((x (pop xs))) (print x)) is equivalent to (while (when-let ((x (pop xs))) (print x) t)) The last expression `t` is added so that regardless of the return value of the last form in BODY, the while loop continues, unless a binding value is nil. Signed-off-by: Lucius Hu --- lisp/emacs-lisp/subr-x.el | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el index 9c8c967ee9..3203cce455 100644 --- a/lisp/emacs-lisp/subr-x.el +++ b/lisp/emacs-lisp/subr-x.el @@ -156,6 +156,13 @@ are non-nil, then the result is non-nil." ,@(or body `(,res)))) `(let* () ,@(or body '(t)))))) +(defmacro while-let* (varlist &rest body) + "Bind variables according to VARLIST and conditionally evaluate BODY. +This is like `while-let' but doesn't handle a VARLIST of the form +\(SYMBOL SOMETHING) sepcially." + (declare (indent 1) (debug if-let*)) + (list 'while (list 'if-let* varlist (nconc (macroexp-progn body) (list t))))) + ;;;###autoload (defmacro if-let (spec then &rest else) "Bind variables according to SPEC and evaluate THEN or ELSE. @@ -193,6 +200,15 @@ The variable list SPEC is the same as in `if-let'." (declare (indent 1) (debug if-let)) (list 'if-let spec (macroexp-progn body))) +;;;###autoload +(defmacro while-let (spec &rest body) + "Bind variables according to SPEC and conditionally evaluate BODY. +Evaluate each binding in turn, stopping if a binding value is nil. +BODY is repeatedly evaluated until a binding value is nil. +The return value is always nil." + (declare (indent 1) (debug if-let)) + (list 'while (list 'if-let spec (nconc (macroexp-progn body) (list t))))) + (defsubst hash-table-empty-p (hash-table) "Check whether HASH-TABLE is empty (has 0 elements)." (zerop (hash-table-count hash-table))) -- 2.31.1