Added anaphor.clj, simple anaphoric macros (aif, awhen, ...).

1 files changed, 55 insertions, 0 deletions

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+;;; anaphor.clj -- Anaphoric macros for Clojure
+
+;; by Stuart Sierra <mail@stuartsierra.com>
+;; April 7, 2008
+
+;; Copyright (c) 2008 Stuart Sierra. All rights reserved.  The use and
+;; distribution terms for this software are covered by the Common
+;; Public License 1.0 (http://www.opensource.org/licenses/cpl1.0.php)
+;; which can be found in the file CPL.TXT at the root of this
+;; distribution.  By using this software in any fashion, you are
+;; agreeing to be bound by the terms of this license.  You must not
+;; remove this notice, or any other, from this software.
+
+
+;; This file defines some simple anaphoric macros for Clojure.
+;;
+;; See "On Lisp" for a description of anaphoric macros:
+;; http://www.bookshelf.jp/cgi-bin/goto.cgi?file=onlisp&node=Anaphoric+Macros
+;;
+;; The macros defined in this file differ slightly from the anaphoric
+;; macros in "On Lisp" in that they each take a symbol as their first
+;; argument.  That symbol is the "anaphor" (for which "On Lisp" always
+;; uses "it").  This follows Clojure's preference for non-capturing
+;; macros.
+
+
+(clojure/in-ns 'anaphor)
+(clojure/refer 'clojure)
+
+(defmacro aif
+  "Like 'if', but binds the result of the test to 'symbol' in the
+  body."
+  ([symbol test then]
+   `(let [~symbol ~test]
+      (if ~symbol ~then)))
+  ([symbol test then else]
+   `(let [~symbol ~test]
+      (if ~symbol ~then ~else))))
+
+(defmacro awhen
+  "Like 'when', but binds the result of the test to 'symbol' in the
+  body."
+  [symbol test & body]
+  `(aif ~symbol ~test
+	(do ~@body)))
+
+(defmacro acond
+  "Like 'cond', but binds the result of each test to 'symbol' in the
+  expression body."
+  [symbol & clauses]
+  (when clauses
+    (list 'aif symbol (first clauses)
+	  (second clauses)
+	  (cons 'acond (cons symbol (rest (rest clauses)))))))
+