feat(stdlib): Add Array.tryInit

[spotandjake]

This pr adds an Array.tryInit function to make this a bit easier. Array.tryInit: (length: Number, fn: (index: Number) => Result<a, b>) => Result<Array<A>, b>. This makes building arrays from result functions quite a bit easier as there was no good alternative before. I do not love the tryInit name but I couldn't think of anything better.

Notes:

• I do not love the tryInit name, if anyone has a better one let me know
• If we like the feature and name I am happy to add it to List and Array.Immutable
  • happy todo that in this pr or a separate one
  • Array.tryInit is the most important as with something like a list you can just build it manually.
• I also noticed we didn't have tests for Array.make and Array.init so I added those in this pr but I am happy to move those to a separate pr if wanted.

[spotandjake]

We incRef when we add the items so we should probably decRef all the items we incRef'd. I would appreciate if someone could verify that I am doing this right.

I also think we might need to manually deallocate (not just decref) the allocated array if i'm not mistaken?

[ospencer]

This feels a little niche. Can you give some examples of use cases of where this would be useful?

[spotandjake]

This feels a little niche. Can you give some examples of use cases of where this would be useful?

The scenario I needed this for was parsing wasm, I already know how many types will be in the section so it makes sense to initialize the array ahead of time, but I need to parse each type separately like:

let typeCount = Stream.GetAndAdvance.uLeb128(stream)
Array.init((_) => {
  parseWasmType(stream) // This could fail so we want to escape
}, typeCount)

The only other ideal way I could think todo this was either use a list or create an array of options (which has other issues). I know the instruction itself seems niche and my use case was niche but I feel like the operation makes sense especially during streaming operations where you know the count but not if the data is correct.

[ospencer]

I see. Let me sit with it for a bit.