From 69a5f6d3582c0208d2b7c8b3036cdfd6729e88f2 Mon Sep 17 00:00:00 2001
From: Kaz Kylheku <kaz@kylheku.com>
Date: Mon, 14 Nov 2016 07:19:41 -0800
Subject: New in-package macro.

* lisplib.c (package_set_entries): Add in-package
symbol name to autload list.

* share/txr/stdlib/package.tl (in-package): New macro.

* txr.1: Documented.
---
 lisplib.c                   |  2 +-
 share/txr/stdlib/package.tl |  7 +++++++
 txr.1                       | 25 +++++++++++++++++++++++++
 3 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/lisplib.c b/lisplib.c
index 38c002ce..713bb480 100644
--- a/lisplib.c
+++ b/lisplib.c
@@ -410,7 +410,7 @@ static val getopts_instantiate(val set_fun)
 static val package_set_entries(val dlt, val fun)
 {
   val name[] = {
-    lit("defpackage"),
+    lit("defpackage"), lit("in-package"),
     nil
   };
   set_dlt_entries(dlt, name, fun);
diff --git a/share/txr/stdlib/package.tl b/share/txr/stdlib/package.tl
index 1827628f..7e62b6e5 100644
--- a/share/txr/stdlib/package.tl
+++ b/share/txr/stdlib/package.tl
@@ -81,3 +81,10 @@
        ,*(unless (assoc :use clauses) ^((use-package "usr" ,pkg)))
        ,*exp-clauses
        ,pkg)))
+
+(defmacro in-package (pkg)
+  (unless (or (symbolp pkg) (stringp pkg))
+    (throwf 'eval-error "~s: ~s isn't a package name" 'in-package pkg))
+  ^(set *package* (or (find-package ',pkg)
+                      (throwf 'eval-error "~s: no such package: ~s"
+                              'in-package ',pkg))))
diff --git a/txr.1 b/txr.1
index 27fa0cae..b692d6f0 100644
--- a/txr.1
+++ b/txr.1
@@ -39797,6 +39797,31 @@ removed with
 and the name is interned again.
 .RE
 
+.coNP Macro @ in-package
+.synb
+.mets (in-package << name )
+.syne
+.desc
+The
+.code in-package
+macro causes the
+.code *package*
+special variable to take on the package denoted by
+.metn name .
+The macro checks, at expansion time, that
+.meta name
+is either a string or symbol. An error is thrown if
+this isn't the case.
+
+The
+.meta name
+argument expression isn't evaluated, and so must not be quoted.
+
+The code generated by the macro performs a search for the
+package; if the package is not found at the time when
+the macro's expansion is evaluated. An error is thrown if
+the package isn't found.
+
 .SS* Pseudo-random Numbers
 .coNP Special variable @ *random-state*
 .desc
-- 
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