fixes #53: properly escape output of Show instance for String

Author: michaelficarra

src/Prelude.js

@@ -214,7 +214,27 @@ exports.showCharImpl = function (c) {
 };
 
 exports.showStringImpl = function (s) {
-  return JSON.stringify(s);
+  var l = s.length;
+  return "\"" + s.replace(
+    /[\0-\x1F\x7F"\\]/g,
+    function (c, i) { // jshint ignore:line
+      switch (c) {
+        case "\"":
+        case "\\":
+          return "\\" + c;
+        case "\a": return "\\a";
+        case "\b": return "\\b";
+        case "\f": return "\\f";
+        case "\n": return "\\n";
+        case "\r": return "\\r";
+        case "\t": return "\\t";
+        case "\v": return "\\v";
+      }
+      var k = i + 1;
+      var empty = k < l && s[k] >= "0" && s[k] <= "9" ? "\\&" : "";
+      return "\\" + c.charCodeAt(0).toString(10) + empty;
+    }
+  ) + "\"";
 };
 
 exports.showArrayImpl = function (f) {