From 38bb7375b93b048be6331e3376e091e7506e0fde Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Sun, 5 Feb 2017 16:11:00 -0800
Subject: Adding whena macro.

We have ifa and conda; whena is conspicuously absent.

* lisplib.c (ifa_set_entries): Add autoload entry for whena.

* share/txr/stdlib/ifa.tl (whena): New macro.

* txr.1: Documented whena.
---
 lisplib.c               |  4 +++-
 share/txr/stdlib/ifa.tl |  3 +++
 txr.1                   | 17 +++++++++++++++++
 3 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/lisplib.c b/lisplib.c
index abdd8c1c..d5f0d1d1 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -106,7 +106,9 @@ static val ver_instantiate(val set_fun)
 
 static val ifa_set_entries(val dlt, val fun)
 {
-  val name[] = { lit("ifa"), lit("conda"), lit("condlet"), nil };
+  val name[] = {
+    lit("ifa"), lit("whena"), lit("conda"), lit("condlet"), nil
+  };
   set_dlt_entries(dlt, name, fun);
   return nil;
 }
diff --git a/share/txr/stdlib/ifa.tl b/share/txr/stdlib/ifa.tl
index 170e8eb5..e99d5d40 100644
--- a/share/txr/stdlib/ifa.tl
+++ b/share/txr/stdlib/ifa.tl
@@ -66,6 +66,9 @@
                   (if (,sym ,*(if (eq 'dwim sym) ^(,(second test)))
                             ,*temps) ,then ,else)))))))))
 
+(defmacro whena (test . body)
+  ^(ifa ,test (progn ,*body)))
+
 (macro-time
   (defun sys:if-to-cond (if-oper cond-oper pairs)
     (tree-case pairs
diff --git a/txr.1 b/txr.1
index 65c6c940..9bdc0cd4 100644
--- a/txr.1
+++ b/txr.1
@@ -14283,6 +14283,23 @@ as well as the anaphoric
 .code it
 variable feature.
 
+.coNP Macro @ whena
+.synb
+.mets (whena < test << form *)
+.syne
+.desc
+The
+.code whena
+macro is similar to the
+.code when
+macro, except that it is anaphoric in exactly the same manner as the
+.code ifa
+macro. It may be understood as conforming to the following equivalence:
+
+.cblk
+  (whena x f0 f2 ...)  <-->  (if x (progn f0 f2 ...))
+.cble
+
 .coNP Macro @ dotimes
 .synb
 .mets (dotimes >> ( var < count-form <> [ result-form ]) << body-form *)
-- 
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