Widening a Term in Scala 3 macro

Question
1

Hi!

I’m trying to generically convert a constructor like Function2[A, B, C] into Function1[(A, B), C].

In my macro I use Select:

val ctor: Term = ???
val tupled = Select.unique(ctor, "tupled")

But later, when I use tupled.asExprOf[Tuple => Any] I’m getting the following compile-time error:

   |Exception occurred while executing macro expansion.
   |java.lang.Exception: Expr cast exception: ((a: scala.Boolean, f: rs$line$1.Foo) => new rs$line$1.Bar(a, f)).tupled
   |of type: scala.Function2[scala.Boolean, rs$line$1.Foo, rs$line$1.Bar].tupled
   |did not conform to type: scala.Function1[scala.Tuple, scala.Any]

So, for some reasons .tupled part was not invoked.

I figure out that on TypeRef-level I can get rid of it with widen method, but how do I get rid of it on Term-level?

2

I think you just get an error because ((Boolean, Foo)) => Bar is not a subtype of Tuple => Any. That’s because the input type parameter of a function is contravariant.

3

I thought about that, but switching to Nothing => Any (neither Any => Nothing) did not help.