implement array comprehension

test/fixtures/array-comprehension/if/actual.js

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+var seattlers = [for (c of customers) if (c.city == "Seattle") { name: c.name, age: c.age }];

test/fixtures/array-comprehension/if/expected.js

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+var seattlers = function () {
+  var _arr = [];
+  customers.forEach(function (c) {
+    if (c.city == "Seattle") {
+      _arr.push({
+        name: c.name,
+        age: c.age
+      });
+    }
+  });
+  return _arr;
+}();

test/fixtures/array-comprehension/multiple/actual.js

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+var arr = [for (x of "abcdefgh".split("")) for (y of "12345678".split("")) (x + y)];

test/fixtures/array-comprehension/multiple/expected.js

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+var arr = (function () {
+  var _arr = [];
+
+  "abcdefgh".split("").forEach(function (x) {
+    "12345678".split("").forEach(function (y) {
+      _arr.push(x + y);
+    });
+  });
+
+  return _arr;
+})();

test/fixtures/array-comprehension/no-in/actual.js

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+var arr = [for (i in [1, 2, 3]) i * i];

test/fixtures/array-comprehension/no-in/options.json

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+{
+  "throws": "for-in array comprehension is not supported"
+}

test/fixtures/array-comprehension/single/actual.js

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+var arr = [for (i of [1, 2, 3]) i * i];

test/fixtures/array-comprehension/single/expected.js

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+var arr = (function () {
+  var _arr = [];
+
+  [1, 2, 3].forEach(function (i) {
+    _arr.push(i * i);
+  });
+
+  return _arr;
+})();