I’m trying to figure out why function equality is considered hard (or undecidable). Is it because of an overly aggressive definition of equality? For example, I can understand why it would be difficult to determine that two implementations of a function were identical without comparing the generate…

[image] MarkHamburg: I’m trying to figure out why function equality is considered hard (or undecidable). Is it because of an overly aggressive definition of equality? The two paragraphs below are perhaps false because over-simplified. Elm is a language for doing computations. It is not a la…

Example: Being able to test function equality makes it easier to do certain forms of caching which makes it easier to build more performant web pages. Elm’s built-in support for lazy HTML is an example of such a thing but it isn’t the only such thing. More broadly for better web pages, function equ…

@MarkHamburg claims two benefits for function equality being part of Elm’s run-time, quicker pages and fewer crashes. I’m not convinced. (Sorry for the long message - I think the detail helps. Disclaimer: I’m an Elm beginner, with much experience in pure mathematics and logic.) Quicker web pages I…

This is a very interesting topic. Since functions are objects in JS perhaps we could assign an id property to a function and take a page out of cryptographies book and hash the arguments and function id into a unique string for equality check? But personally I would rather we avoid that performanc…

I wonder if Unison can bring any new insights to this topic

[image] pd-andy: Elm already compromises on its “no runtime error” guarantee with function equality, I’d rather it compromised on == 's integrity and just said all functions are false unless referentially equal. I think this would be a more practical trade-off. Using reference equality in thi…

The thing that makes me more scared about the function equality strategy is that, unlike JS – where I’m the metal defining functions myself and I know they have the references I expect – when I’m in Elm I have no idea how my definitions (lazy? auto-curried?) will turn into actual javascript function…

I think there is one place where function equality is commonly useful: Occasionally, one wants to create (or use) semi-generic data structures that require more information about the values of a given type than equality. For example, a Dict needs an order on the keys and a HashSet would need a hash …

I’ve spent some time reading the Elm generated JavaScript and I think in practice the behaviour isn’t surprising, so luckily this potential problem is easy to avoid.

I was ready to let this wind down having gotten early on Evan’s definitive view that he would prefer functions be declared equal if they computed the same thing which really is impossible to compute. I just think that then argues for a type system mechanism to prevent such equality checks from sneak…

Function equality

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lpil July 19, 2021, 6:48am 18

I think this would be a more practical trade-off. Using reference equality in this one case seems less surprising and less likely to cause production problems to me.

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Function equality

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