use a template in tail call transformer - @RReverser

lib/6to5/transformation/templates/tail-call-body.js

@@ -0,0 +1,13 @@
+{
+  var ARGUMENTS_ID = arguments,
+      THIS_ID = this,
+      SHOULD_CONTINUE_ID,
+      RESULT_ID;
+
+  do {
+    SHOULD_CONTINUE_ID = false;
+    RESULT_ID = FUNCTION.apply(THIS_ID, ARGUMENTS_ID);
+  } while(SHOULD_CONTINUE_ID);
+
+  return RESULT_ID;
+}

lib/6to5/transformation/transformers/es6/tail-call.js

@@ -1,6 +1,7 @@
 "use strict";
 
-var t = require("../../../types");
+var util = require("../../../util");
+var t    = require("../../../types");
 
 function returnBlock(expr) {
   return t.blockStatement([t.returnStatement(expr)]);
@@ -17,6 +18,7 @@ function transformExpression(node, scope, state) {
         if (!callConsequent && !callAlternate) {
           return;
         }
+
         // if ternary operator had tail recursion in value, convert to optimized if-statement
         node.type = "IfStatement";
         node.consequent = callConsequent ? t.toBlock(callConsequent) : returnBlock(node.consequent);
@@ -33,6 +35,7 @@ function transformExpression(node, scope, state) {
         if (!callRight) {
           return;
         }
+
         // cache left value as it might have side-effects
         var leftId = state.getLeftId();
         var testExpr = t.assignmentExpression(
@@ -47,16 +50,19 @@ function transformExpression(node, scope, state) {
 
       case "SequenceExpression":
         var seq = node.expressions;
+
         // only last element can be optimized
         var lastCall = subTransform(seq[seq.length - 1]);
         if (!lastCall) {
           return;
         }
+
         // remove converted expression from sequence
         // and convert to regular expression if needed
         if (--seq.length === 1) {
           node = seq[0];
         }
+
         return [t.expressionStatement(node)].concat(lastCall);
 
       case "CallExpression":
@@ -68,12 +74,15 @@ function transformExpression(node, scope, state) {
             case "call":
               args = t.arrayExpression(node.arguments.slice(1));
               break;
+
             case "apply":
               args = node.arguments[1] || t.identifier("undefined");
               break;
+
             default:
               return;
           }
+
           thisBinding = node.arguments[0];
           callee = callee.object;
         }
@@ -91,11 +100,13 @@ function transformExpression(node, scope, state) {
             state.getArgumentsId(),
             args || t.arrayExpression(node.arguments)
           )),
+
           t.expressionStatement(t.assignmentExpression(
             "=",
             state.getThisId(),
             thisBinding || t.identifier("undefined")
           )),
+
           t.returnStatement(t.assignmentExpression(
             "=",
             state.getShouldContinueId(),
@@ -152,15 +163,19 @@ exports.FunctionExpression = function (node, parent, scope) {
   var state = {
     hasTailRecursion: false,
     ownerId: ownerId,
+
     getArgumentsId: function () {
       return argumentsId = argumentsId || scope.generateUidIdentifier("arguments");
     },
+
     getThisId: function () {
       return thisId = thisId || scope.generateUidIdentifier("this");
     },
+
     getShouldContinueId: function () {
       return shouldContinueId = shouldContinueId || scope.generateUidIdentifier("shouldContinue");
     },
+
     getLeftId: function () {
       return leftId = leftId || scope.generateUidIdentifier("left");
     }
@@ -182,32 +197,11 @@ exports.FunctionExpression = function (node, parent, scope) {
   var resultId = scope.generateUidIdentifier("result");
   state.getShouldContinueId();
 
-  node.body = t.blockStatement([
-    t.variableDeclaration("var", [
-      t.variableDeclarator(argumentsId, t.identifier("arguments")),
-      t.variableDeclarator(thisId, t.thisExpression()),
-      t.variableDeclarator(shouldContinueId),
-      t.variableDeclarator(resultId)
-    ]),
-    t.doWhileStatement(t.blockStatement([
-      t.expressionStatement(t.assignmentExpression(
-        "=",
-        shouldContinueId,
-        t.literal(false)
-      )),
-      t.expressionStatement(t.assignmentExpression(
-        "=",
-        resultId,
-        t.callExpression(
-          t.memberExpression(
-            t.functionExpression(null, node.params, block),
-            t.identifier("apply"),
-            false
-          ),
-          [thisId, argumentsId]
-        )
-      ))
-    ]), shouldContinueId),
-    t.returnStatement(resultId)
-  ]);
+  node.body = util.template("tail-call-body", {
+    SHOULD_CONTINUE_ID: shouldContinueId,
+    ARGUMENTS_ID:       argumentsId,
+    RESULT_ID:          resultId,
+    FUNCTION:           t.functionExpression(null, node.params, block),
+    THIS_ID:            thisId,
+  });
 };