From 7b0341d13bab3e7c2202327d56d150e2c7887045 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Fri, 15 May 2015 07:03:44 -0700
Subject: Variables are now deletable places, if they are global.

* place.tl (sys:sym-delete-expander): New function.
(get-delete-expander): Retrieve delete expander for
symbols.
---
 ChangeLog |  8 ++++++++
 place.tl  | 20 ++++++++++++++++----
 txr.1     |  2 +-
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 77a01b0d..82fcffbb 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-05-15  Kaz Kylheku  <kaz@kylheku.com>
+
+	Variables are now deletable places, if they are global.
+
+	* place.tl (sys:sym-delete-expander): New function.
+	(get-delete-expander): Retrieve delete expander for
+	symbols.
+
 2015-05-15  Kaz Kylheku  <kaz@kylheku.com>
 
 	* eval.c (symbol_value): Retrieve the binding of a symbol
diff --git a/place.tl b/place.tl
index d421d4fa..85b0a55f 100644
--- a/place.tl
+++ b/place.tl
@@ -72,6 +72,17 @@
                         ,',place-expr ,val-expr)))
          ,op-body))
 
+    (defun sys:sym-delete-expander (deleter-name
+                                    place-expr . op-body)
+      ^(macrolet ((,deleter-name (:env env)
+                    (when (lexical-var-p env ',place-expr)
+                      (sys:eval-err "~s is a lexical variable, thus not deletable"
+                                    ',place-expr))
+                    ^(prog1
+                       (symbol-value ',',place-expr)
+                       (makunbound ',',place-expr))))
+         ,*op-body))
+
     (defun get-update-expander (place)
       (cond
         ((symbolp place) (fun sys:sym-update-expander))
@@ -89,10 +100,11 @@
         (t (sys:eval-err "form ~s is not syntax denoting an assignable place" place))))
 
     (defun get-delete-expander (place)
-      (if (consp place)
-        (or [*place-delete-expander* (car place)]
-            (sys:eval-err "~s is not a deletable place" place))
-        (sys:eval-err "form ~s is not syntax denoting a deletable place" place))))
+      (cond
+        ((symbolp place) (fun sys:sym-delete-expander))
+        ((consp place) (or [*place-delete-expander* (car place)]
+                           (sys:eval-err "~s is not a deletable place" place)))
+        (t (sys:eval-err "form ~s is not syntax denoting a deletable place" place)))))
 
   (defmacro rlet (bindings :env e . body)
     (let ((exp-bindings (mapcar (aret ^(,@1 ,(macroexpand @2 e))) bindings)))
diff --git a/txr.1 b/txr.1
index 7c6328fa..39331d63 100644
--- a/txr.1
+++ b/txr.1
@@ -11840,7 +11840,7 @@ operator binding is returned, and if that doesn't exist, then
 .code nil
 is returned.
 
-The value of a macro binding isn't a functio object, but a list of the
+The value of a macro binding isn't a function object, but a list of the
 following form:
 
 .cblk
-- 
cgit v1.2.3