New condlet macro; small change to iflet/whenlet.

* eval.c (me_iflet_whenlet): Allow the test form
to be an atomic expression instead of bindings.
This allows iflet to be used as the sole target
construct of condlet, while allowing condlet to
have a fallback clause with t. It also means that
an empty list of bindings is allowed (since it
is the atom nil).

* lisplib.c (ifa_set_entries): Add "condlet" to
the autoload names for the ifa module. That's
where we are adding condlet.

* share/txr/stdlib/ifa.tl (sys:if-to-cond): New
macro expander helper function, generalizing the writing
cond-like macros based on if-like operators.
(conda): Rewritten using sys:if-to-cond.
(condlet): New macro.

* txr.1: Documented change in iflet/whenlet.
Documented condlet.

1 files changed, 12 insertions, 5 deletions

diff --git a/share/txr/stdlib/ifa.tl b/share/txr/stdlib/ifa.tl
index cefb38eb..42b4d99c 100644
--- a/share/txr/stdlib/ifa.tl
+++ b/share/txr/stdlib/ifa.tl
@@ -65,9 +65,16 @@
                   (if (,sym ,*(if (eq 'dwim sym) ^(,(second test)))
                             ,*temps) ,then ,else)))))))))
 
+(macro-time
+  (defun sys:if-to-cond (if-oper cond-oper pairs)
+    (tree-case pairs
+      (((test . forms) . rest) ^(,if-oper ,test (progn ,*forms)
+                                          (,cond-oper ,*rest)))
+      (() ())
+      (else (throwf 'eval-error "~s: bad syntax: ~s" cond-oper pairs)))))
+
 (defmacro conda (. pairs)
-  (tree-case pairs
-    (((test . forms) . rest) ^(ifa ,test (progn ,*forms)
-                                   (conda ,*rest)))
-    (() ())
-    (else (throwf 'eval-error "conda: bad syntax: ~s" pairs))))
+  (sys:if-to-cond 'ifa 'conda pairs))
+
+(defmacro condlet (. pairs)
+  (sys:if-to-cond 'iflet 'condlet pairs))