Brendan Eich wrote:
On May 14, 2009, at 6:04 PM, Waldemar Horwat wrote:
Brendan Eich wrote:
On May 14, 2009, at 1:47 PM, Waldemar Horwat wrote:
This whole thing is another nail in the coffin of generators.
Generators are the root of the troublesome longjmp's which don't
play well with others.
Are you talking about generators, or lambdas?
Generators. They cause control flow to jump around between two
independent functions.
THe same problem occurs without lambdas:
function gen(arg) {
try {
yield 1;
yield 2;
} finally {
alert("Finally called up to three times?!");
}
}
That finally will be called either 1, 2, or 3 times depending on what
the caller does, which violates the principle that finally is called
exactly once, no matter how you leave a scope.
Did you actually test this? Firefox 2 and up work the same.
js> g = gen()
[object Generator]
js> g.next()
1
js> g.next()
2
js> g.next()
typein:6: ReferenceError: alert is not defined
js> alert=print
function print() {
[native code]
}
js> g = gen(42)
[object Generator]
js> g.next()
1
js> g.next()
2
js> g.next()
Finally called up to three times?!
uncaught exception: [object StopIteration]
Exactly one finally.
That behavior is wrong in the case that g gets forgotten after calling next
just once. You're silently exiting through a finally clause without calling it.
Waldemar
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