improve performance of sequence wrapper

Author: andrew-coleman

src/functions.js

@@ -13,8 +13,6 @@ const functions = (() => {
     var isArrayOfStrings = utils.isArrayOfStrings;
     var isArrayOfNumbers = utils.isArrayOfNumbers;
     var createSequence = utils.createSequence;
-    // var isSequence = utils.isSequence;
-    // var toSequence = utils.toSequence;
     var isFunction = utils.isFunction;
     var isLambda = utils.isLambda;
     var isIterable = utils.isIterable;

src/jsonata.js

@@ -29,7 +29,6 @@ var jsonata = (function() {
     var isArrayOfNumbers = utils.isArrayOfNumbers;
     var createSequence = utils.createSequence;
     var isSequence = utils.isSequence;
-    var toSequence = utils.toSequence;
     var isFunction = utils.isFunction;
     var isLambda = utils.isLambda;
     var isIterable = utils.isIterable;
@@ -113,11 +112,11 @@ var jsonata = (function() {
                 break;
         }
 
-        if(environment.lookup('__jsonata_async') &&
+        if(environment.async &&
           (typeof result === 'undefined' || result === null || typeof result.then !== 'function')) {
             result = Promise.resolve(result);
         }
-        if(environment.lookup('__jsonata_async') && typeof result.then === 'function' && expr.nextFunction && typeof result[expr.nextFunction] === 'function') {
+        if(environment.async && typeof result.then === 'function' && expr.nextFunction && typeof result[expr.nextFunction] === 'function') {
             // although this is a 'thenable', it is chaining a different function
             // so don't yield since yielding will trigger the .then()
         } else {
@@ -142,7 +141,12 @@ var jsonata = (function() {
             if(expr.keepArray) {
                 result.keepSingleton = true;
             }
-            result = result.value();
+            if(result.length === 0) {
+                result = undefined;
+            } else if(result.length === 1) {
+                result =  result.keepSingleton ? result : result[0];
+            }
+
         }
 
         return result;
@@ -849,7 +853,8 @@ var jsonata = (function() {
         for (var item = lhs, index = 0; item <= rhs; item++, index++) {
             result[index] = item;
         }
-        return toSequence(result);
+        result.sequence = true;
+        return result;
     }
 
     /**
@@ -1606,7 +1611,8 @@ var jsonata = (function() {
                 }
                 return value;
             },
-            timestamp: enclosingEnvironment ? enclosingEnvironment.timestamp : null
+            timestamp: enclosingEnvironment ? enclosingEnvironment.timestamp : null,
+            async: enclosingEnvironment ? enclosingEnvironment.async : false
         };
     }
 
@@ -1854,7 +1860,7 @@ var jsonata = (function() {
                 var result, it;
                 // if a callback function is supplied, then drive the generator in a promise chain
                 if(typeof callback === 'function') {
-                    exec_env.bind('__jsonata_async', true);
+                    exec_env.async = true;
                     var catchHandler = function (err) {
                         populateMessage(err); // possible side-effects on `err`
                         callback(err, null);

src/utils.js

@@ -59,7 +59,8 @@ const utils = (() => {
      * @returns {Array} - empty sequence
      */
     function createSequence() {
-        var sequence = toSequence([]);
+        var sequence = [];
+        sequence.sequence = true;
         if (arguments.length === 1) {
             sequence.push(arguments[0]);
         }
@@ -72,52 +73,7 @@ const utils = (() => {
      * @returns {boolean} true if it's a sequence
      */
     function isSequence(value) {
-        var sequence = value.sequence;
-        if(sequence === true) {
-            var desc = Object.getOwnPropertyDescriptor(value, 'sequence');
-            if(desc.enumerable === false) {
-                return true;
-            }
-        }
-        return false;
-    }
-
-    /**
-     * Converts an array to a result sequence (by adding special properties)
-     * @param {Array} arr - the array to convert
-     * @returns {*} - the sequence
-     */
-    function toSequence(arr) {
-        Object.defineProperty(arr, 'sequence', {
-            enumerable: false,
-            configurable: false,
-            get: function () {
-                return true;
-            }
-        });
-        Object.defineProperty(arr, 'keepSingleton', {
-            enumerable: false,
-            configurable: false,
-            writable: true,
-            value: false
-        });
-        Object.defineProperty(arr, 'value', {
-            enumerable: false,
-            configurable: false,
-            get: function () {
-                return function() {
-                    switch (this.length) {
-                        case 0:
-                            return undefined;
-                        case 1:
-                            return this.keepSingleton ? this : this[0];
-                        default:
-                            return this;
-                    }
-                };
-            }
-        });
-        return arr;
+        return value.sequence === true && Array.isArray(value);
     }
 
     /**
@@ -175,7 +131,6 @@ const utils = (() => {
         isArrayOfNumbers,
         createSequence,
         isSequence,
-        toSequence,
         isFunction,
         isLambda,
         isIterable,