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| -rw-r--r-- | src/clojure/contrib/condp.clj | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/src/clojure/contrib/condp.clj b/src/clojure/contrib/condp.clj new file mode 100644 index 00000000..4f7c0dd2 --- /dev/null +++ b/src/clojure/contrib/condp.clj @@ -0,0 +1,49 @@ +;;; condp.clj - generic case-like macro using template expressions + +;; By Stuart Sierra, http://stuartsierra.com/ +;; December 15, 2008 + +;; Copyright (c) Stuart Sierra, 2008. All rights reserved. The use +;; and distribution terms for this software are covered by the Eclipse +;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php) +;; which can be found in the file epl-v10.html 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. + + +(ns clojure.contrib.condp + (:require clojure.contrib.template)) + +(defmacro condp + "expr is a template expression (see template), clauses are test/expr + pairs like cond. Evalautes the template on each test value, one at + a time. If a test returns logical true, condp evaluates the + corresponding expr and returns its value. If none of the tests are + true, and there are an odd number of clauses, the last clause is + evaluated, otherwise returns nil." + [expr & clauses] + (let [test-fn-sym (gensym "test_") + f (fn this [c] + (cond + (empty? c) nil + (= 1 (count c)) (first c) + :else (list 'if (list test-fn-sym (first c)) + (second c) + (this (rrest c)))))] + `(let [~test-fn-sym (clojure.contrib.template/template ~expr)] + ~(f clauses)))) + +(defmacro econdp + "Like condp but throws Exception if no tests match." + [expr & clauses] + (let [test-fn-sym (gensym "test_") + f (fn this [c] + (cond + (empty? c) '(throw (Exception. "Nothing matched in econdp.")) + (= 1 (count c)) (throw (IllegalStateException. "Odd number of clauses in econdp.")) + :else (list 'if (list test-fn-sym (first c)) + (second c) + (this (rrest c)))))] + `(let [~test-fn-sym (clojure.contrib.template/template ~expr)] + ~(f clauses)))) |