cond-let--when$: New macro

2 files changed, 39 insertions, 2 deletions

diff --git a/cond-let-tests.el b/cond-let-tests.el
index dca81dc..e4302b9 100644
--- a/cond-let-tests.el
+++ b/cond-let-tests.el
@@ -437,9 +437,30 @@
     (let ((anon1 1))
       (when anon1 2))))
 
+(ert-deftest cond-let-test--105-expand--when$ ()
+  (cond-let-test--macroexpansion nil 3
+
+    (when$ (+ 0 1)
+      (+ $ 2))
+
+    (let (($ (+ 0 1)))
+      (when $
+        (+ $ 2))))
+
+  (cond-let-test--macroexpansion nil 4
+
+    (when$ (+ 0 1)
+      (cl-incf $)
+      (+ $ 2))
+
+    (let (($ (+ 0 1)))
+      (when $
+        (cl-incf $)
+        (+ $ 2)))))
+
 ;;; While
 
-(ert-deftest cond-let-test--111-expand--while-let* ()
+(ert-deftest cond-let-test--112-expand--while-let* ()
   (let ((n 5))
     (cond-let-test--macroexpansion nil nil
       (while-let* ((a (setq n (1- n)))
@@ -454,7 +475,7 @@
                 (print a)
               (throw ':while-let*2 nil))))))))
 
-(ert-deftest cond-let-test--112-expand--while-let ()
+(ert-deftest cond-let-test--113-expand--while-let ()
   (let ((n 5))
     (cond-let-test--macroexpansion nil nil
       (while-let ((a (setq n (1- n)))
@@ -479,6 +500,7 @@
 ;;   ("and>"      . "cond-let--and>")
 ;;   ("and-let"   . "cond-let--and-let")
 ;;   ("if-let"    . "cond-let--if-let")
+;;   ("when$"     . "cond-let--when$")
 ;;   ("when-let"  . "cond-let--when-let")
 ;;   ("while-let" . "cond-let--while-let"))
 ;; End:
diff --git a/cond-let.el b/cond-let.el
index b2a64f6..28038d3 100644
--- a/cond-let.el
+++ b/cond-let.el
@@ -441,6 +441,21 @@ and return nil.
               (when ,lastvar
                 ,bodyform ,@body))))))
 
+(defmacro cond-let--when$ (varform bodyform &rest body)
+  "Bind variable `$' to value of VARFORM and conditionally evaluate BODY.
+
+If VARFORM yields a non-nil value, bind the symbol `$' to that value,
+evaluate BODY with that binding in effect, and return the value of the
+last form.  If VARFORM yields nil, do not evaluate BODY, and return nil.
+BODY must be one or more expressions.  If VARLIST is empty, do nothing
+and return nil.
+
+\(fn VARLIST BODY...)"
+  (declare (debug (form form)))
+  `(let (($ ,varform))
+     (when $
+       ,bodyform ,@body)))
+
 ;;; While
 
 (defmacro cond-let--while-let* (varlist &rest body)