Brendan Eich wrote:
> Kevin Smith wrote:
>> I wonder if you'd need to go back to the lexer in some cases:
>>
>>     function(a = let) {
>>       "use strict";
>>     }
>>
>> After seeing the "use strict", I'd have to go back and re-scan the 
>> "let" to find out that it was actually a keyword in this context (and 
>> hence a syntax error).
>
> The current spec definitely makes 'let' reserved only in strict mode, 
> but we have no let expression forms, so this looks like another case 
> of parsing the kind of example you show above with 'let' in the 
> parameter default value lexed as an Identifier but then rejected 
> during the static semantics phase as an always-an-error-in-expressions 
> reserved word. Good catch. Still tolerable, I think. 

You may be thinking, "Argh, strict mode is deep, so this ought to parse, 
does it require relexing?"

   function f(a = function(){let x = 42; return x}()) {
     "use strict";
     return a;
   }

But IIRC (and from reading 
http://people.mozilla.org/~jorendorff/es6-draft.html, looking for 
LetOrConst uses), ES6 supports let in all contexts, reserved word or not.

Did we really do any good trying to reserve yield *or* let in ES5? I 
don't see it, now.

/be

You may be thinking, "Argh, strict mode is deep, so this ought to parse, 
does it require relexing?"

```js
function f(a = function(){let x = 42; return x}()) {
  "use strict";
  return a;
}
```

But IIRC (and from reading http://people.mozilla.org/~jorendorff/es6-draft.html, looking for 
LetOrConst uses), ES6 supports let in all contexts, reserved word or not.

Did we really do any good trying to reserve yield *or* let in ES5? I 
don't see it, now.