Support Tuple User Fn arguments and return types.

[StachuDotNet]

As of #4182 we won't be allowing users to use tuples quite yet, so this functionality seems safe for now.

There are a few parts:

• type checking in the backend (see below comment)
• add TTuple to allowedParamTypes in Autocomplete.res,
  • this will currently also effect allowedParamTipes
• testing of type checking (TypeChecker.Tests.fs)
• some stdlib functions to be used here^

[StachuDotNet]

Draft of TypeChecker.fs work:

  | TTuple (firstType, secondType, otherTypes), DTuple (first, second, theRest) ->
    // TODO: there's definitely a simpler way to gather these errors, but I'm blanking.
    let errors =
      [ (firstType, first); (secondType, second) ] @ List.zip otherTypes theRest
      |> List.filterMap (fun (t, v) ->
        match unify userTypes t v with
        | Ok () -> None
        | Error err -> Some err)
      |> List.collect (fun errs -> errs)

    match errors with
    | [] -> Ok()
    | errors -> Error errors

[StachuDotNet]

Some commentary here around autocomplete: https://github.com/darklang/dark/pull/4182#discussion_r912372275

[pbiggar]

Some commentary here around autocomplete: #4182 (comment)

Clicking this link doesn't get me anything (I think due to github folding). Might be worth copying the text or conversation if it's valuable.

[StachuDotNet]

Odd. It takes a second to jump to the right place for me, but does.

Copied commentary:

I think this needs code to parse this (and tests!). I think adding tuples to the interestingDvals should find this.

I also get an error in Blazor when calling functions with tuples of 3 or more iterms:

I think we shouldn't support tuple-typed function parameters until we support polymorphic type signatures. With (I think) all the existing types, such as TList, there's an easy conversion from the old value to the new one: Tlist becomes TList TAny. However, in TTuple, we encode the number of type arguments as well as their actual argument. So if someone has a TTuple, and they call it with a tuple with 7 members, how will we know to convert it to TTuple(TAny,TAny,TAny,TAny,TAny,TAny,TAny) instead of TTuple(TAny,TAny).

[pbiggar]

Works in daarklang-next (client part not applicable)