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+;;; Vikalpa --- Prove S-expression
+;;; Copyright © 2020 Masaya Tojo <masaya@tojo.tokyo>
+;;;
+;;; This file is part of Vikalpa.
+;;;
+;;; Vikalpa is free software; you can redistribute it and/or modify it
+;;; under the terms of the GNU General Public License as published by
+;;; the Free Software Foundation; either version 3 of the License, or
+;;; (at your option) any later version.
+;;;
+;;; Vikalpa is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with Vikalpa.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (vikalpa syntax)
+  #:export (define/guard))
+
+(define-syntax-rule (define/guard (name (var pred?) ...) b b* ...)
+  (define (name var ...)
+    (unless (pred? var)
+      (error (format #f
+                     "~a:~%  expected:  ~a~%  given: "
+                     'name
+                     'pred?)
+             var))
+    ...
+    b b* ...))