add playground pretzel maps

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"],