1 files changed, 37 insertions, 0 deletions
diff --git a/lib/utils.js b/lib/utils.js
index 33dc8ff2..d18e62ee 100644
--- a/lib/utils.js
+++ b/lib/utils.js
@@ -214,3 +214,40 @@ function set_intersection(a, b) {
         return b.indexOf(el) >= 0;
     });
 };
+
+// this function is taken from Acorn [1], written by Marijn Haverbeke
+// [1] https://github.com/marijnh/acorn
+function makePredicate(words) {
+    if (!(words instanceof Array)) words = words.split(" ");
+    var f = "", cats = [];
+    out: for (var i = 0; i < words.length; ++i) {
+        for (var j = 0; j < cats.length; ++j)
+            if (cats[j][0].length == words[i].length) {
+                cats[j].push(words[i]);
+                continue out;
+            }
+        cats.push([words[i]]);
+    }
+    function compareTo(arr) {
+        if (arr.length == 1) return f += "return str === " + JSON.stringify(arr[0]) + ";";
+        f += "switch(str){";
+        for (var i = 0; i < arr.length; ++i) f += "case " + JSON.stringify(arr[i]) + ":";
+        f += "return true}return false;";
+    }
+    // When there are more than three length categories, an outer
+    // switch first dispatches on the lengths, to save on comparisons.
+    if (cats.length > 3) {
+        cats.sort(function(a, b) {return b.length - a.length;});
+        f += "switch(str.length){";
+        for (var i = 0; i < cats.length; ++i) {
+            var cat = cats[i];
+            f += "case " + cat[0].length + ":";
+            compareTo(cat);
+        }
+        f += "}";
+        // Otherwise, simply generate a flat `switch` statement.
+    } else {
+        compareTo(words);
+    }
+    return new Function("str", f);
+};