feat(stdlib): Add ability to set seed on Hash.hash

[spotandjake]

This pr adds the ability to set the seed of the hashing function.

I think it might be worth pinning the seed when this is used in Map and Set, which would make marshalling the values work between two separate runs.

[phated]

I don't think we want to allow setting a seed on each hash. Instead, I think we want to add a submodule with a Hash record that has the seed attached and then create a singleton at the top-level module that passes it to the submodule hash. This way people can do Hash.SeededHash.make() and then Hash.SeededHash.hash(hasher, anything)

[spotandjake]

I think this would be more elegant if Hash.SeededHash.make() returned. Function.

Hash.SeededHash.make(seed: Number) -> ((val: a) -> Number) thoughts?

[phated]

I don't hate it! Let's get some other feedback before doing the work.

[alex-snezhko]

I like Jake's idea; however in that case I'm not sure it needs to be in a submodule if it's just one function; maybe could just make a makeSeeded function?

[spotandjake]

I am good with that approach.

[phated]

In the case of the make function, we'd want seed to be defaulted and use that to construct our global hasher, right?

[spotandjake]

I dont think we should make it defaulted I think the api should look like.

module Hash

provide let makeSeeded = (seed) => ((value: a) => Number)
let hash = makeSeeded(currentSeedGenCode)
provide let hash = (value) => hash

we could just directly provide hash but then I think we miss out on the for good graindoc we currently have. Thoughts?

[spotandjake]

I don't actually think we can use the approach I suggested. It doesnt look like the grain type system supports it.

I seem to be getting an error because it cannot generalize the param type in the hash function.

[ospencer]

Yeah, our type system can't really support that right now.

I don't love the idea of the top module and the seeded module having such different APIs. I think the SeededHash module would make more sense if we had functors, e.g. SeededHash.Make() which would give you just a module with a hash function on it.

It'd be breaking, but I'd like to see that same hash(hasher, anything) on both versions, with make and makeSeeded functions to make the hasher.

[phated]

Whoops. Submitted that as a comment.

[spotandjake]

I updated this, due to the issue I ran into above I decided to go with the approach @phated had suggested at first.

I also rewrote the hashing function to avoid a mutable global. while this wasn't necessary I think it reduces the surface area for bugs to pop up.

[phated]

This should be done in a non-breaking way so I'm updating the title

[spotandjake]

Closing in favour of #2170