better control flow for tco continuation - fixes #850 and fixes #822

lib/babel/transformation/templates/tail-call-body.js

@@ -1,3 +1,4 @@
 {
-  FUNCTION_ID:while (true) BLOCK
+  var AGAIN_ID = true;
+  FUNCTION_ID: while (AGAIN_ID) BLOCK
 }

lib/babel/transformation/templates/tail-call.js

@@ -1,23 +0,0 @@
-(function () {
-  function Tail(func, args, context) {
-    this.func = func;
-    this.args = args;
-    this.context = context;
-  }
-
-  Tail.prototype._isTailDescriptor = true;
-
-  var isRunning = false;
-
-  return function (func, args, context) {
-    var result = new Tail(func, args, context);
-    if (!isRunning) {
-      isRunning = true;
-      do {
-        result = result.func.apply(result.context, result.args);
-      } while (result instanceof Tail || (result && result._isTailDescriptor));
-      isRunning = false;
-    }
-    return result;
-  };
-})()

lib/babel/transformation/transformers/es6/tail-call.js

@@ -40,6 +40,10 @@ TailCallTransformer.prototype.getFunctionId = function () {
   return this.functionId = this.functionId || this.scope.generateUidIdentifier("function");
 };
 
+TailCallTransformer.prototype.getAgainId = function () {
+  return this.againId = this.againId || this.scope.generateUidIdentifier("again");
+};
+
 TailCallTransformer.prototype.getParams = function () {
   var params = this.params;
 
@@ -112,9 +116,12 @@ TailCallTransformer.prototype.run = function () {
     body.unshift(t.variableDeclaration("var", paramDecls));
   }
 
-  body.push(t.returnStatement());
+  body.unshift(t.expressionStatement(
+    t.assignmentExpression("=", this.getAgainId(), t.literal(false)))
+  );
 
   node.body = util.template("tail-call-body", {
+    AGAIN_ID:      this.getAgainId(),
     THIS_ID:       this.thisId,
     ARGUMENTS_ID:  this.argumentsId,
     FUNCTION_ID:   this.getFunctionId(),
@@ -288,6 +295,9 @@ TailCallTransformer.prototype.subTransformCallExpression = function (node) {
     }
   }
 
+  body.push(t.expressionStatement(
+    t.assignmentExpression("=", this.getAgainId(), t.literal(true))
+  ));
   body.push(t.continueStatement(this.getFunctionId()));
 
   return body;

test/fixtures/transformation/es6-tail-call/call-apply/expected.js

@@ -4,7 +4,10 @@
   var _this = this,
       _arguments = arguments;
 
-  _function: while (true) {
+  var _again = true;
+
+  _function: while (_again) {
+    _again = false;
     var n = _x;
 
     if (n <= 0) {
@@ -14,10 +17,12 @@
 
     if (Math.random() > 0.5) {
       _arguments = [_x = n - 1];
+      _again = true;
       continue _function;
     } else {
       _arguments = [_x = n - 1];
+      _again = true;
       continue _function;
-    }return;
+    }
   }
 })(1000000) === "foo";

test/fixtures/transformation/es6-tail-call/expression-consequent/expected.js

@@ -1,10 +1,14 @@
 "use strict";
 
 function f() {
-  _function: while (true) {
+  var _again = true;
+
+  _function: while (_again) {
+    _again = false;
+
     if (true) {} else {
+      _again = true;
       continue _function;
     }
-    return;
   }
 }

test/fixtures/transformation/es6-tail-call/expressions/expected.js

@@ -3,7 +3,10 @@
 (function f(_x) {
   var _left;
 
-  _function: while (true) {
+  var _again = true;
+
+  _function: while (_again) {
+    _again = false;
     var n = _x;
     if (n <= 0) {
       return "foo";
@@ -19,7 +22,8 @@
       }
 
       _x = n - 1;
+      _again = true;
       continue _function;
-    }return;
+    }
   }
 })(1000000, true) === "foo";

test/fixtures/transformation/es6-tail-call/factorial/expected.js

@@ -2,16 +2,19 @@
 
 function fact(_x2) {
   var _arguments = arguments;
+  var _again = true;
 
-  _function: while (true) {
+  _function: while (_again) {
+    _again = false;
     var n = _x2;
     acc = undefined;
     var acc = _arguments[1] === undefined ? 1 : _arguments[1];
     if (n > 1) {
       _arguments = [_x2 = n - 1, acc * n];
+      _again = true;
       continue _function;
     } else {
       return acc;
-    }return;
+    }
   }
 }

test/fixtures/transformation/es6-tail-call/recursion/expected.js

@@ -2,10 +2,12 @@
 
 (function f(_x2) {
   var _arguments = arguments;
+  var _again = true;
 
-  _function: while (true) {
+  _function: while (_again) {
     var g = function g() {};
 
+    _again = false;
     var n = _x2;
     m = local1 = local2 = local3 = undefined;
     var m = _arguments[1] === undefined ? getDefaultValue() : _arguments[1];
@@ -21,7 +23,7 @@
     // `g` should be function here on each pass
     g = 123;
     _arguments = [_x2 = n - 1];
+    _again = true;
     continue _function;
-    return;
   }
 })(1000000, true) === "foo";

test/fixtures/transformation/es6-tail-call/try-catch/expected.js

@@ -11,7 +11,10 @@
 })(1000000) === "foo";
 
 (function f(_x) {
-  _function: while (true) {
+  var _again = true;
+
+  _function: while (_again) {
+    _again = false;
     var n = _x;
 
     if (n <= 0) {
@@ -22,9 +25,9 @@
       throw new Error();
     } catch (e) {
       _x = n - 1;
+      _again = true;
       continue _function;
     }
-    return;
   }
 })(1000000) === "foo";
 
@@ -41,7 +44,10 @@
 })(1000000) === "foo";
 
 (function f(_x) {
-  _function: while (true) {
+  var _again = true;
+
+  _function: while (_again) {
+    _again = false;
     var n = _x;
 
     if (n <= 0) {
@@ -50,8 +56,8 @@
 
     try {} finally {
       _x = n - 1;
+      _again = true;
       continue _function;
     }
-    return;
   }
 })(1000000) === "foo";