For context for future readers, this has to do with animation easing
functions from another thread
have not constructed such a library, so I won't comment.
On Wednesday, October 12, 2016 at 2:43:58 PM UTC-5, Zinggi wrote:
> I also think that comparing functions should just compare them by
> reference, this should cover the most common cases.
> Another possible solution: What about a compile time error? Is this
> On Wednesday, 12 October 2016 18:48:12 UTC+2, Mark Hamburg wrote:
>> As discussed elsewhere, the runtime exception related to function
>> equality comparisons is a lurking time bomb for code that is really only
>> addressed on a multi-developer project by being paranoid both about
>> functions in data structures and use of the equality operator. Both points
>> of paranoia get in the way of writing "good" code. There are other
>> arguments around things like serialization for avoiding using functions in
>> some places, but there are lots of other places where it is extremely
>> useful to put functions in data structures. (Imagine writing an effects
>> manager if it couldn't store functions in its data structures.)
>> Full equality tests are, as I understand it, undecidable. That doesn't
>> mean, however, that some limited analysis can't prove equality in most of
>> the conditions that matter. In fact, the existing code doesn't always throw
>> an exception. It only throws an exception if an "allocation identity" test
>> fails. One could extend this to looking at the "code pointer" and
>> allocation identity for the closure values and probably get many of the
>> remaining cases that mattered. It's just a matter of how far one wants to
>> push when trying to prove or disprove equality and I'm not arguing for a
>> particular limit here.
>> Rather, I think the central issue is around what happens when we give up.
>> At that point, there are two choices: throw a runtime exception as happens
>> now or return false. As mentioned above and discussed at further length
>> elsewhere, the runtime exception leads to paranoid coding. What are the
>> issues with returning false? The big problem with returning false is that
>> this means that some compiler optimizations might then change cases that
>> returned false without the optimizations into cases that returned true and
>> people become understandably uncomfortable with the possibility that
>> compiler optimizations could change the meaning of programs. And with that,
>> I've more or less wanted a "return false" answer but convinced myself that
>> throwing an exception wasn't unjustified and that maybe what we needed
>> instead was type system support to avoid the issue.
>> But then this morning's discussion of the virtual DOM had me realizing
>> that runtime optimizations around when the render-diff-patch algorithm gets
>> run create significant potential for variable program behavior. We embrace
>> these optimizations even though they introduce non-determinism. Now, its
>> non-determinism at the level of the physical DOM rather than the values
>> produced in Elm itself — i.e., runtime v linguistic non-determinism — but
>> its non-determinism in one of the most fundamental parts about how Elm is
>> generally used so that distinction seems somewhat arbitrary.
>> I think Elm makes the right call on the DOM. Maybe it should log cases
>> where the DOM logic can recognize that there might be a problem, but I
>> think this is overall a tradeoff worth making.
>> But by the same argument, I think Elm programs would be better if the
>> runtime exception for function equality comparisons was replaced with a
>> false result even though it might actually be true. And if it's really
>> irksome, then it could generate a log statement as well.
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