New macro: expander-let.

* stdlib/expander-let.tl: New file.

* autoload.c (expander_let_set_entries, expander_let_instantiate);
New static functions.
(autoload_init): Register autoloading of above new file via
above new functions.

* txr.1: Documented.

* stdlib/doc-syms.tl: Updated.

2 files changed, 45 insertions, 0 deletions

diff --git a/stdlib/doc-syms.tl b/stdlib/doc-syms.tl
index 6391695f..a3d5434d 100644
--- a/stdlib/doc-syms.tl
+++ b/stdlib/doc-syms.tl
@@ -673,6 +673,7 @@
       ("expand-left" "N-00E168FE")
       ("expand-right" "N-023B6B64")
       ("expand-with-free-refs" "N-0334827B")
+      ("expander-let" "N-00DBD46D")
       ("expt" "D-0076")
       ("exptmod" "D-0036")
       ("extproc" "N-0072FF5E")
diff --git a/stdlib/expander-let.tl b/stdlib/expander-let.tl
new file mode 100644
index 00000000..72338793
--- /dev/null
+++ b/stdlib/expander-let.tl
@@ -0,0 +1,44 @@
+;; Copyright 2023
+;; 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.
+
+(defmacro usr:expander-let (:form f :env e vars . body)
+  (let (syms values)
+    (each ((pair vars))
+      (tree-case pair
+        ((sym init)
+         (unless (special-var-p sym)
+           (compile-warning f "~s is required to be a special variable" sym))
+         (push sym syms)
+         (push
+           (if-match (sys:dv-bind @sym @form) init
+             (eval form)
+             (eval init))
+           values))
+        (else
+          (compile-warning f "not a var-init form: ~s" else))))
+    (progv (nreverse syms) (nreverse values)
+           (expand ^(progn ,*body) e))))