add playground pretzel maps

doc/playground.md

@@ -18,6 +18,7 @@ to5.transform("code", { playground: true });
 
  * [Memoization operator](#memoization-operator)
  * [Method binding](#method-binding)
+ * [Pretzel map](#pretzel-map)
 
 ### Memoization assignment operator
 
@@ -61,5 +62,16 @@ var fn = obj.method.bind(obj);
 var fn = obj.method.bind(obj, "foob");
 ```
 
-**NOTE:** Method binding can **only** be used as an **expression** and not as
-statement.
+### Pretzel map
+
+```javascript
+["foo", "bar"].map(:toUpperCase); // ["FOO", "BAR"]
+[1.1234, 23.53245, 3].map(:toFixed(2)); // ["1.12", "23.53", "3.00"]
+```
+
+equivalent to:
+
+```javascript
+["foo", "bar"].map(function (val) { return val.toUpperCase(); });
+[1.1234, 23.53245, 3].map(function (val) { return val.toFixed(2); });
+```

lib/6to5/generation/generators/playground.js

@@ -1,6 +1,6 @@
 var _ = require("lodash");
 
-_.each(["BindMemberExpression"], function (type) {
+_.each(["BindMemberExpression", "PretzelMapExpression"], function (type) {
   exports[type] = function () {
     throw new ReferenceError("Trying to render non-standard playground node " + JSON.stringify(type));
   };

lib/6to5/patch.js

@@ -38,6 +38,12 @@ def("BindMemberExpression")
   .field("property", or(def("Identifier"), def("Expression")))
   .field("arguments", [def("Expression")]);
 
+def("PretzelMapExpression")
+  .bases("Expression")
+  .build("callee", "arguments")
+  .field("callee", def("Expression"))
+  .field("arguments", [def("Expression")]);
+
 types.finalize();
 
 var estraverse = require("estraverse");

lib/6to5/transformation/transform.js

@@ -59,6 +59,7 @@ _.each({
   // plyground
   methodBinding:             require("./transformers/playground-method-binding"),
   memoizationOperator:       require("./transformers/playground-memoization-operator"),
+  pretzelMap:                require("./transformers/playground-pretzel-map"),
 
   _blockHoist:               require("./transformers/_block-hoist"),
   _declarations:             require("./transformers/_declarations"),

lib/6to5/transformation/transformers/playground-pretzel-map.js

@@ -0,0 +1,29 @@
+var t = require("../../types");
+var _ = require("lodash");
+
+exports.PretzelMapExpression = function (node, parent, file, scope) {
+  var buildCall = function (args) {
+    var param = file.generateUidIdentifier("val", scope);
+    return t.functionExpression(null, [param], t.blockStatement([
+      t.returnStatement(t.callExpression(t.memberExpression(param, node.callee), args))
+    ]));
+  };
+
+  if (_.find(node.arguments, t.isDynamic)) {
+    var argsIdName = file.generateUid("args", scope);
+    var argsId = t.identifier(argsIdName);
+    scope.push({
+      key: argsIdName,
+      id: argsId
+    });
+
+    return t.sequenceExpression([
+      t.assignmentExpression("=", argsId, t.arrayExpression(node.arguments)),
+      buildCall(node.arguments.map(function (node, i) {
+        return t.memberExpression(argsId, t.literal(i), true);
+      }))
+    ]);
+  } else {
+    return buildCall(node.arguments);
+  }
+};

lib/6to5/types/visitor-keys.json

@@ -44,6 +44,7 @@
   "ObjectExpression":          ["properties"],
   "ObjectPattern":             ["properties"],
   "ParenthesizedExpression":   ["expression"],
+  "PretzelMapExpression":      ["callee", "arguments"],
   "Program":                   ["body"],
   "Property":                  ["key", "value"],
   "ReturnStatement":           ["argument"],

package.json

@@ -47,7 +47,7 @@
     "chokidar": "0.11.1",
     "source-map-support": "0.2.8",
     "esutils": "1.1.6",
-    "acorn-6to5": "0.9.1-8",
+    "acorn-6to5": "0.9.1-9",
     "estraverse": "1.8.0",
     "private": "0.1.6"
   },

test/fixtures/transformation/playground/pretzel-map/actual.js

@@ -0,0 +1,7 @@
+["foo", "bar"].map(:toUpperCase);
+[1.1234, 23.53245, 3].map(:toFixed(2));
+
+var get = function () {
+  return 2;
+};
+[1.1234, 23.53245, 3].map(:toFixed(get()));

test/fixtures/transformation/playground/pretzel-map/exec.js

@@ -0,0 +1,7 @@
+assert.deepEqual(["foo", "bar"].map(:toUpperCase), ["FOO", "BAR"]);
+assert.deepEqual([1.1234, 23.53245, 3].map(:toFixed(2)), ["1.12", "23.53", "3.00"]);
+
+var get = function () {
+  return 2;
+}
+assert.deepEqual([1.1234, 23.53245, 3].map(:toFixed(get())), ["1.12", "23.53", "3.00"]);

test/fixtures/transformation/playground/pretzel-map/expected.js

@@ -0,0 +1,16 @@
+"use strict";
+
+var _args;
+["foo", "bar"].map(function (_val) {
+  return _val.toUpperCase();
+});
+[1.1234, 23.53245, 3].map(function (_val2) {
+  return _val2.toFixed(2);
+});
+
+var get = function () {
+  return 2;
+};
+[1.1234, 23.53245, 3].map((_args = [get()], function (_val3) {
+  return _val3.toFixed(_args[0]);
+}));