;; Various useful macros
;;
;; Everybody is invited to add their own little macros here!
;;
;; 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.macros)

;; By Konrad Hinsen
(defmacro const
  "Evaluate the constant expression expr at compile time."
  [expr]
  (eval expr))

;; By Konrad Hinsen
(defmacro letfn
  "A variant of let for local function definitions. fn-bindings consists
   of name/args/body triples, with (letfn [name args body] ...)
   being equivalent to (let [name (fn name args body)] ...)."
  [fn-bindings & exprs]
  (let [makefn (fn [[name args body]] (list name (list 'fn name args body)))
	fns (vec (apply concat (map makefn (partition 3 fn-bindings))))]
  `(let ~fns ~@exprs)))

;; By Konrad Hinsen
(defmacro lazy-and-standard-branch
  "Comile the first expression in the lazy branch of Clojure, and the second
   one in the standard branch."
  [lazy-expr standard-expr]
  (if (find (ns-map (find-ns 'clojure.core)) 'lazy-seq)
    lazy-expr
    standard-expr))