quasiquote with unquote-splicing

quasiquote.clj

(ns quasiquote
  (:use clojure.test))

;; **************************************
;; Quasiquote from ClojureQL
;; http://gitorious.org/clojureql/clojureql/blobs/master/src/dk/bestinclass/clojureql/util.clj
;; modified to work with unquote-splicing
;; **************************************

;; Original copyright notice from the util.clj file
;; (current file is a modified fragment of that file):

;; Copyright (c) 2008,2009 Lau B. Jensen <lau.jensen {at} bestinclass.dk
;;                         Meikel Brandmeyer <mb {at} kotka.de>
;; 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 LICENSE.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.

(defn self-eval?
  "Check whether the given form is self-evaluating."
  [obj]
  (or (keyword?  obj)
      (number?   obj)
      (instance? Character obj)
      (string?   obj)
      (nil?      obj)))

(defn flatten-map
  "Flatten the keys and values of a map into a list."
  [the-map]
  (reduce (fn [result entry] (-> result
                               (conj (key entry))
                               (conj (val entry))))
          [] the-map))

(defn unquote?
  "Tests whether the given form is of the form (unquote ...)."
  [form]
  (and (seq? form) (= (first form) `unquote)))

(defn unquote-splicing?
  "Tests whether the given form is of the form (unquote ...)."
  [form]
  (and (seq? form) (= (first form) `unquote-splicing)))

(declare quasiquote*)

(defn quasiquote-for-splicing [form]
  (let [need-splice (unquote-splicing? form)
        quasiquoted (quasiquote* form)]
    (if need-splice
      quasiquoted
      `(list ~quasiquoted))))

(defn concat-code-for-splicing [form]
  (cons `concat (map quasiquote-for-splicing form)))

(defn quasiquote*
  "Worker for quasiquote macro. See docstring there. For use in macros."
  [form]
  (cond
    (self-eval? form) form
    (unquote? form)   (second form)
    (unquote-splicing? form) (second form)
    (symbol? form)    (list 'quote form)
    (vector? form)    (cons `vec (list (concat-code-for-splicing form)))
    (map? form)       (apply hash-map (map quasiquote* (flatten-map form)))
    (set? form)       (list* `apply `hash-set (list (concat-code-for-splicing form)))
    (seq? form)       (concat-code-for-splicing form)
    :else             (list 'quote form)))

(defmacro quasiquote
  "Quote the supplied form as quote does, but evaluate unquoted parts.

  Example: (let [x 5] (quasiquote (+ ~x 6))) => (+ 5 6)"
  [form]
  (quasiquote* form))

(deftest test-quasiquote-unquote-splicing
  (is (= '[+ a b d e o u]
         (let [x '(d e)] (quasiquote [+ a b ~@x o u]))))
  (is (= '(+ a b d e o u)
         (let [x '(d e)] (quasiquote (+ a b ~@x o u)))))
  (is (= '#{+ a b d e o u}
         (let [x '(d e)] (quasiquote #{+ a b ~@x o u}))))
  (is (= '[1 2 #{a b}]
         (let [x (quasiquote (a b))] (quasiquote [1 2 #{~@x}]))))
  (is (= '[1 2 #{(a b)}]
         (let [x (quasiquote (a b))] (quasiquote [1 2 #{~x}])))))