Added support for Tuples

[FetBoba]

No description provided.

[LPTK]

Neat! This looks well done to me. WDYT @Derppening?

[Derppening]

Apart from some fields that appear to be better located in Ctx than WatBuilder, the rest looks good to me.

Please do add documentation where possible, including private members.

[Derppening]

Please address the comments and also add some brief documentation for the private functions.

[Derppening]

Is there a reason why this needs to be a lambda and not just a simple Expr that evaluates to a single non-negative integer?

[FetBoba]

I think it needs to be lambda otherwise we end up with duplicating the index computation in both branches because we only get correct tupleRef inside each branch. And also negative indices require array.len(tupleRef)

[Derppening]

Question: If tupleExpr evaluates to an expression with possible side effects (e.g. a function call), would this repeated use of tupleExpr here cause the expression to be emitted 3 times and invoked twice during execution?

For example, in makePair(1, 2).[1], would makePair(1, 2) be evaluated twice?

If so, it may be worth it to generate a temporary local to store the result of tupleExpr, roughly like:

(if
  (local.tee $_tmp
    (ref.test (...))
  (then
    (array.get
      (ref.cast
        (local.get $_tmp)))

(local.tee sets the result of the child expression into the local, and returns the same value.)

[FetBoba]

ok I added local.tee but it required extra handling for temp locals

[Derppening]

The idxI32 expression is emitted three times and will be executed twice during runtime, similar to this comment.

[FetBoba]

ok