On May 17, 2009, at 1:11 PM, Brendan Eich wrote:
On May 17, 2009, at 12:43 PM, Mark S. Miller wrote:
On Sun, May 17, 2009 at 11:00 AM, Brendan Eich
<[email protected]> wrote:
Analogous to direct vs. indirect eval in ES5 (15.1.2.1.1), there
is no
purely syntactic specification for what Neil proposes. A runtime
check is
required. So I don't see why you are focusing only on syntax here.
I don't follow. What runtime check? For the eval operator, the
runtime
check is whether the value of the eval variable is the original
global
eval function. It makes no sense to have a corresponding global yield
function value.
If we reserve yield then you're right.
It's goofy to have
return w;
delete x.y;
typeof z;
yield a; => SyntaxError! must use yield(a)
The mandatory parentheses could be avoided by breaking from Python's
precedent and making yield a canonical unary (that is,
high-)precedence operator like delete, !, etc. But then almost any
algebraic or logical expression computing the value to yield would
need parentheses, and people would make mistakes such as yield a + b
where they meant yield(a + b) -- as in Python -- but got yield(a) + b.
This is one reason, if I recall some PEP text correctly, why Python
requires parentheses around all yield expressions except those on the
right of assignment operators in assignment statements, and in yield
statements. It seems best to require explicit parentheses when yield
is part of a larger expression, no matter the precedence of its
optional argument/operand.
But when there's no larger expression, why require gratuitous
parentheses?
/be
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