add Parsimmon.alt for more efficient .or() chaining

examples/json.js

@@ -7,14 +7,15 @@ var lazy = Parsimmon.lazy;
 
 var json = (function() {
   var json = lazy(function() {
-    return object
-      .or(array)
-      .or(stringLiteral)
-      .or(numberLiteral)
-      .or(nullLiteral)
-      .or(trueLiteral)
-      .or(falseLiteral)
-      .skip(regex(/^\s*/m));
+    return alt([
+      object,
+      array,
+      stringLiteral,
+      numberLiteral,
+      nullLiteral,
+      trueLiteral,
+      falseLiteral
+    ]).skip(regex(/^\s*/m));
   });
 
   var escapes = {

src/parsimmon.js

@@ -68,13 +68,7 @@ Parsimmon.Parser = P(function(_, _super, Parser) {
 
   // -*- primitive combinators -*- //
   _.or = function(alternative) {
-    var self = this;
-
-    return Parser(function(stream, i) {
-      var result = self._(stream, i);
-
-      return result.status ? result : furthestBacktrackFor(alternative._(stream, i), result);
-    });
+    return alt([this, alternative]);
   };
 
   _.then = function(next) {
@@ -303,7 +297,18 @@ Parsimmon.Parser = P(function(_, _super, Parser) {
 
       return furthestBacktrackFor(makeSuccess(i, accum), result);
     });
-  }
+  };
+
+  var alt = Parsimmon.alt = function(parsers) {
+    return Parser(function(stream, i) {
+      var result;
+      for (var j = 0; j < parsers.length; j += 1) {
+        result = furthestBacktrackFor(parsers[j]._(stream, i), result);
+        if (result.status) return result;
+      }
+      return result;
+    });
+  };
 
   var index = Parsimmon.index = Parser(function(stream, i) {
     return makeSuccess(i, i);