Useful Tuple type matches

[nicolasstucki]

We already have a type match Tuple.Map.

We could also have:

• Tuple.Fold (Add Tuple match types #9217)
• Tuple.Filter (Add Filter type to Tuple #9235)
• Tuple.FlatMap (Add Tuple match types #9217)

We can take inspiration for the type matches we already have in Tuple. For example Size is just a fold.

[nicolasstucki]

Fold prototype:

type Fold[Z, F[_, _], T <: Tuple] = T match
  case EmptyTuple => Z
  case h *: t => F[h, Fold[Z, t]]

type Size[T <: Tuple] = Fold[0, [X, Y] => S[X], T]

[nicolasstucki]

FlatMap prototype :

  type FlatMap[Tup <: Tuple, F[_]] <: Tuple = Tup match
    case EmptyTuple => EmptyTuple
    case h *: t => F[h] ++ FlatMap[t, F]

[nicolasstucki]

Not sure how the predicate of a Filter should look like. It could be a type P[_] that returns the type true or the type false.

[nicolasstucki]

Does anyone have other suggestions for the Filter?

[julienrf]

Not sure how the predicate of a Filter should look like. It could be a type P[_] that returns the type true or the type false.

That sounds reasonable. How could we filter all the elements of a tuple that have type Foo with such a predicate type?

[X] => X match { case Foo => true case _ => false }

?

[anatoliykmetyuk]

I came up with the following implementation of the Filter type: #9235.