Clarification needed on SetMutableBinding on a Declarative Environment Record

Mark S. Miller erights at
Sat Jun 5 21:56:14 PDT 2010

On Sat, Jun 5, 2010 at 9:41 PM, Mark S. Miller <erights at> wrote:

> On SpiderMonkey, WebKit, and V8 and, I see

Opera too.

>  var bar = function foo(f) { if (f) {foo = f; foo();} else {print(33);} };
> bar(function(){print(44);});
> 33
> which is the behavior I would normally have expected for non-strict code.
> The reason the assignment to foo correctly doesn't take is that a named
> FunctionExpression brings its name into scope with CreateImmutableBinding
> and InitializeImmutableBinding (See the 2nd FunctionExpression production
> semantics at the top of chapter 13). For strict mode code I would expect the
> failed assignment to fail with a thrown error, but I would normally not have
> been surprised by the silent error for non-strict code. That is, until
> rereading the following text from SetMutableBinding(N,V,S):
> [...] If the binding is an immutable binding, a
> TypeError is always thrown. The S argument is ignored
> because strict mode does not change the meaning of
> setting bindings in declarative environment records.
> Am I misunderstanding something, or 2) was this the intended spec, or 3)
> are these three browsers all non-conformant in the same manner? If the 3rd,
> I'll file bugs on this. If the 2nd, should we add a correction to the ES5
> errata?
> --
>     Cheers,
>     --MarkM

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