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1 ;;; strint.clj -- String interpolation for Clojure
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2 ;; originally proposed/published at http://muckandbrass.com/web/x/AgBP
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3
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4 ;; by Chas Emerick <cemerick@snowtide.com>
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5 ;; December 4, 2009
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6
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7 ;; Copyright (c) Chas Emerick, 2009. All rights reserved. The use
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8 ;; and distribution terms for this software are covered by the Eclipse
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9 ;; Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
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10 ;; which can be found in the file epl-v10.html at the root of this
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11 ;; distribution. By using this software in any fashion, you are
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12 ;; agreeing to be bound by the terms of this license. You must not
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13 ;; remove this notice, or any other, from this software.
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14
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15 (ns
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16 ^{:author "Chas Emerick",
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17 :doc "String interpolation for Clojure."}
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18 clojure.contrib.strint)
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19
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20 (defn- silent-read
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21 "Attempts to clojure.core/read a single form from the provided String, returning
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22 a vector containing the read form and a String containing the unread remainder
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23 of the provided String. Returns nil if no valid form can be read from the
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24 head of the String."
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25 [s]
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26 (try
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27 (let [r (-> s java.io.StringReader. java.io.PushbackReader.)]
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28 [(read r) (slurp r)])
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29 (catch Exception e))) ; this indicates an invalid form -- the head of s is just string data
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30
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31 (defn- interpolate
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32 "Yields a seq of Strings and read forms."
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33 ([s atom?]
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34 (lazy-seq
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35 (if-let [[form rest] (silent-read (subs s (if atom? 2 1)))]
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36 (cons form (interpolate (if atom? (subs rest 1) rest)))
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37 (cons (subs s 0 2) (interpolate (subs s 2))))))
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38 ([^String s]
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39 (if-let [start (->> ["~{" "~("]
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40 (map #(.indexOf s %))
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41 (remove #(== -1 %))
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42 sort
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43 first)]
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44 (lazy-seq (cons
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45 (subs s 0 start)
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46 (interpolate (subs s start) (= \{ (.charAt s (inc start))))))
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47 [s])))
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48
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49 (defmacro <<
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50 "Takes a single string argument and emits a str invocation that concatenates
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51 the string data and evaluated expressions contained within that argument.
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52 Evaluation is controlled using ~{} and ~() forms. The former is used for
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53 simple value replacement using clojure.core/str; the latter can be used to
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54 embed the results of arbitrary function invocation into the produced string.
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55
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56 Examples:
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57 user=> (def v 30.5)
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58 #'user/v
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59 user=> (<< \"This trial required ~{v}ml of solution.\")
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60 \"This trial required 30.5ml of solution.\"
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61 user=> (<< \"There are ~(int v) days in November.\")
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62 \"There are 30 days in November.\"
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63 user=> (def m {:a [1 2 3]})
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64 #'user/m
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65 user=> (<< \"The total for your order is $~(->> m :a (apply +)).\")
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66 \"The total for your order is $6.\"
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67
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68 Note that quotes surrounding string literals within ~() forms must be
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69 escaped."
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70 [string]
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71 `(str ~@(interpolate string)))
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72
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