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diff --git a/stdlib/package.tl b/stdlib/package.tl
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+;; Copyright 2016-2021
+;; Kaz Kylheku <kaz@kylheku.com>
+;; Vancouver, Canada
+;; All rights reserved.
+;;
+;; Redistribution and use in source and binary forms, with or without
+;; modification, are permitted provided that the following conditions are met:
+;;
+;; 1. Redistributions of source code must retain the above copyright notice, this
+;;    list of conditions and the following disclaimer.
+;;
+;; 2. Redistributions in binary form must reproduce the above copyright notice,
+;;    this list of conditions and the following disclaimer in the documentation
+;;    and/or other materials provided with the distribution.
+;;
+;; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+;; ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+;; WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+;; DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+;; FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+;; DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+;; SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+;; CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+;; OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+;; OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+(defun sys:name-str (kind sym-or-string)
+  (cond
+    ((symbolp sym-or-string) (symbol-name sym-or-string))
+    ((stringp sym-or-string) sym-or-string)
+    (t (throw 'eval-error "~s: ~s isn't a valid ~a name"
+              'defpackage sym-or-string kind))))
+
+(defmacro defpackage (name . clauses)
+  (let* ((pkg (gensym "pkg-"))
+         (nstr (sys:name-str 'package name))
+         (exp-clauses (append-each ((c clauses))
+                        (tree-case c
+                          ((keyword package . rest)
+                            (caseql keyword
+                              (:use-from
+                                ^((let ((p (find-package ',package)))
+                                    (unless p
+                                      (throwf 'eval-error
+                                              "~s: no such package: ~s"
+                                              'defpackage ',package))
+                                    (each ((n ',(mapcar (op sys:name-str 'symbol)
+                                                        rest)))
+                                      (let ((s (intern n p)))
+                                        (unless (eq (symbol-package s) p)
+                                          (throwf 'eval-error
+                                                  "~s: won't use non-local ~s from ~s"
+                                                  'defpackage s p))
+                                        (use-sym s ,pkg))))))
+                              (t :)))
+                          ((keyword . rest)
+                            (caseql keyword
+                              (:use
+                                (if rest ^((use-package ',rest ,pkg))))
+                              (:use-syms
+                                ^((each ((s ',rest))
+                                    (use-sym s ,pkg))))
+                              (:local
+                                ^((each ((n ',(mapcar (op sys:name-str 'symbol)
+                                                      rest)))
+                                    (let ((s (intern n ,pkg)))
+                                      (unless (eq (symbol-package s) ,pkg)
+                                        (unuse-sym s ,pkg)
+                                        (intern n ,pkg))))))
+                              (:fallback
+                                (if rest ^((set-package-fallback-list ,pkg
+                                                                      ',rest))))
+                              (:use-from
+                                 (throwf 'eval-error
+                                         "~s: :use-from clause needs package argument"
+                                          'defpackage))
+                              (t :)))
+                          (atom
+                            (throwf 'eval-error "~s: invalid clause: ~s"
+                                    'defpackage atom))))))
+    ^(let ((,pkg (or (find-package ,nstr)
+                     (make-package ,nstr))))
+       ,*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))))