strint per Chas Emerick

src/main/clojure/clojure/contrib/strint.clj

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+;;; strint.clj -- String interpolation for Clojure
+;; originally proposed/published at http://muckandbrass.com/web/x/AgBP
+
+;; by Chas Emerick <cemerick@snowtide.com>
+;; December 4, 2009
+
+;; Copyright (c) Chas Emerick, 2009. 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
+  #^{:author "Chas Emerick",
+     :doc "String interpolation for Clojure."}
+  clojure.contrib.strint
+ (:use [clojure.contrib.io :only (slurp*)]))
+
+(defn- silent-read
+  "Attempts to clojure.core/read a single form from the provided String, returning
+   a vector containing the read form and a String containing the unread remainder
+   of the provided String.  Returns nil if no valid form can be read from the
+   head of the String."
+  [s]
+  (try
+    (let [r (-> s java.io.StringReader. java.io.PushbackReader.)]
+      [(read r) (slurp* r)])
+    (catch Exception e))) ; this indicates an invalid form -- the head of s is just string data
+
+(defn- interpolate
+  "Yields a seq of Strings and read forms."
+  ([s atom?]
+    (lazy-seq
+      (if-let [[form rest] (silent-read (subs s (if atom? 2 1)))]
+        (cons form (interpolate (if atom? (subs rest 1) rest)))
+        (cons (subs s 0 2) (interpolate (subs s 2))))))
+  ([#^String s]
+    (if-let [start (->> ["~{" "~("]
+                     (map #(.indexOf s %))
+                     (remove #(== -1 %))
+                     sort
+                     first)]
+      (lazy-seq (cons
+                  (subs s 0 start)
+                  (interpolate (subs s start) (= \{ (.charAt s (inc start))))))
+      [s])))
+
+(defmacro <<
+  "Takes a single string argument and emits a str invocation that concatenates
+   the string data and evaluated expressions contained within that argument.
+   Evaluation is controlled using ~{} and ~() forms.  The former is used for
+   simple value replacement using clojure.core/str; the latter can be used to
+   embed the results of arbitrary function invocation into the produced string.
+
+   Examples:
+   user=> (def v 30.5)
+   #'user/v
+   user=> (<< \"This trial required ~{v}ml of solution.\")
+   \"This trial required 30.5ml of solution.\"
+   user=> (<< \"There are ~(int v) days in November.\")
+   \"There are 30 days in November.\"
+   user=> (def m {:a [1 2 3]})
+   #'user/m
+   user=> (<< \"The total for your order is $~(->> m :a (apply +)).\")
+   \"The total for your order is $6.\"
+
+   Note that quotes surrounding string literals within ~() forms must be
+   escaped."
+  [string]
+  `(str ~@(interpolate string)))
+

src/test/clojure/clojure/contrib/test_strint.clj

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+;   Copyright (c) Stuart Halloway, 2010-. 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.test-strint
+  (:use clojure.test)
+  (:use [clojure.contrib strint with-ns]))
+
+(def silent-read (with-ns 'clojure.contrib.strint silent-read))
+(def interpolate (with-ns 'clojure.contrib.strint interpolate))
+
+(deftest test-silent-read
+  (testing "reading a valid form returns [read form, rest of string]"
+    (is (= [[1] "[2]"] (silent-read "[1][2]"))))
+  (testing "reading an invalid form returns nil"
+    (is (= nil (silent-read "[")))))
+
+(deftest test-interpolate
+  (testing "a plain old string"
+    (is (= ["a plain old string"] (interpolate "a plain old string"))))
+  (testing "some value replacement forms"
+    (is (= '["" foo " and " bar ""] (interpolate "~{foo} and ~{bar}"))))
+  (testing "some fn-calling forms"
+    (is (= '["" (+ 1 2) " and " (vector 3) ""] (interpolate "~(+ 1 2) and ~(vector 3)")))))
+
+(deftest test-<<
+  (testing "docstring examples"
+    (let [v 30.5
+          m {:a [1 2 3]}]
+      (is (= "This trial required 30.5ml of solution."
+             (<< "This trial required ~{v}ml of solution.")))
+      (is (= "There are 30 days in November."
+             (<< "There are ~(int v) days in November.")))
+      (is (= "The total for your order is $6."
+             (<< "The total for your order is $~(->> m :a (apply +))."))))))