rlm@10: ;;; strint.clj -- String interpolation for Clojure
rlm@10: ;; originally proposed/published at http://muckandbrass.com/web/x/AgBP
rlm@10: 
rlm@10: ;; by Chas Emerick <cemerick@snowtide.com>
rlm@10: ;; December 4, 2009
rlm@10: 
rlm@10: ;; Copyright (c) Chas Emerick, 2009. All rights reserved.  The use
rlm@10: ;; and distribution terms for this software are covered by the Eclipse
rlm@10: ;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
rlm@10: ;; which can be found in the file epl-v10.html at the root of this
rlm@10: ;; distribution.  By using this software in any fashion, you are
rlm@10: ;; agreeing to be bound by the terms of this license.  You must not
rlm@10: ;; remove this notice, or any other, from this software.
rlm@10: 
rlm@10: (ns
rlm@10:   ^{:author "Chas Emerick",
rlm@10:      :doc "String interpolation for Clojure."}
rlm@10:   clojure.contrib.strint)
rlm@10: 
rlm@10: (defn- silent-read
rlm@10:   "Attempts to clojure.core/read a single form from the provided String, returning
rlm@10:    a vector containing the read form and a String containing the unread remainder
rlm@10:    of the provided String.  Returns nil if no valid form can be read from the
rlm@10:    head of the String."
rlm@10:   [s]
rlm@10:   (try
rlm@10:     (let [r (-> s java.io.StringReader. java.io.PushbackReader.)]
rlm@10:       [(read r) (slurp r)])
rlm@10:     (catch Exception e))) ; this indicates an invalid form -- the head of s is just string data
rlm@10: 
rlm@10: (defn- interpolate
rlm@10:   "Yields a seq of Strings and read forms."
rlm@10:   ([s atom?]
rlm@10:     (lazy-seq
rlm@10:       (if-let [[form rest] (silent-read (subs s (if atom? 2 1)))]
rlm@10:         (cons form (interpolate (if atom? (subs rest 1) rest)))
rlm@10:         (cons (subs s 0 2) (interpolate (subs s 2))))))
rlm@10:   ([^String s]
rlm@10:     (if-let [start (->> ["~{" "~("]
rlm@10:                      (map #(.indexOf s %))
rlm@10:                      (remove #(== -1 %))
rlm@10:                      sort
rlm@10:                      first)]
rlm@10:       (lazy-seq (cons
rlm@10:                   (subs s 0 start)
rlm@10:                   (interpolate (subs s start) (= \{ (.charAt s (inc start))))))
rlm@10:       [s])))
rlm@10: 
rlm@10: (defmacro <<
rlm@10:   "Takes a single string argument and emits a str invocation that concatenates
rlm@10:    the string data and evaluated expressions contained within that argument.
rlm@10:    Evaluation is controlled using ~{} and ~() forms.  The former is used for
rlm@10:    simple value replacement using clojure.core/str; the latter can be used to
rlm@10:    embed the results of arbitrary function invocation into the produced string.
rlm@10: 
rlm@10:    Examples:
rlm@10:    user=> (def v 30.5)
rlm@10:    #'user/v
rlm@10:    user=> (<< \"This trial required ~{v}ml of solution.\")
rlm@10:    \"This trial required 30.5ml of solution.\"
rlm@10:    user=> (<< \"There are ~(int v) days in November.\")
rlm@10:    \"There are 30 days in November.\"
rlm@10:    user=> (def m {:a [1 2 3]})
rlm@10:    #'user/m
rlm@10:    user=> (<< \"The total for your order is $~(->> m :a (apply +)).\")
rlm@10:    \"The total for your order is $6.\"
rlm@10: 
rlm@10:    Note that quotes surrounding string literals within ~() forms must be
rlm@10:    escaped."
rlm@10:   [string]
rlm@10:   `(str ~@(interpolate string)))
rlm@10: