||= is much needed?

[John Tamplin]

On Tue, Jun 12, 2012 at 3:09 PM, Brendan Eich <brendan at mozilla.org> wrote:

> And (to be clear) the semantics for
>
> LeftHandSideExpression ?= AssignmentExpression
>
> are roughly
>
> Let lref = evaluate A.
> Let lval = GetValue(lref).
> Let rref = evaluate B.
> Let rval = GetValue(rref).
> Throw a SyntaxError exception if the following conditions are all true:
> • Type(lref) is Reference is true
> • IsStrictReference(lref) is true
> • Type(GetBase(lref)) is Environment Record
> • GetReferencedName(lref) is either "eval" or "arguments"
> If lval is undefined, call PutValue(lref, rval).
>
> to assign the default value if and only if the left-hand side's current
> value is undefined.
>

Wouldn't you want B to be evaluated only if A is undefined?

-- 
John A. Tamplin
Software Engineer (GWT), Google
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