If a match contains a nested match where one or more cases return Never, the return type of the outer match is nil #865

yorickpeterse · 2025-05-16T22:30:19Z

Please describe the bug

The compiler has a feature where if one or more case branches in a match don't return a value, the values of other case branches are also ignored. This way you can write a match where one case does something that happens to return a value while another case returns nil or breaks/returns, and you won't get a type error.

It seems that for nested match expressions this isn't handled correctly as demonstrated by the following:

fn example(value: Int) {}

type async Main {
  fn async main {
    loop {
      let num = match 10 {
        case 10 -> 1
        case 20 -> {
          match 20 {
            case _ -> break
          }
        }
        case _ -> 30
      }

      example(num)
    }
  }
}

This code should compile with num being a value of Int, but instead num is typed as Nil and thus produces the following error:

/tmp/test.inko:16:15 error(invalid-type): expected a value of type 'Int', found 'Nil'

This is not the case if the inner match is replaced with just a break, so something goes wrong when dealing with nested match expressions.

Operating system

Arch Linux

Inko version

main

The text was updated successfully, but these errors were encountered:

yorickpeterse added accepting contributions Issues that are suitable to be worked on by anybody, not just maintainers bug Defects, unintended behaviour, etc compiler Changes related to the compiler labels May 16, 2025

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If a match contains a nested match where one or more cases return Never, the return type of the outer match is nil #865

If a match contains a nested match where one or more cases return Never, the return type of the outer match is nil #865

Uh oh!

If a match contains a nested match where one or more cases return Never, the return type of the outer match is nil #865

If a match contains a nested match where one or more cases return Never, the return type of the outer match is nil #865

Comments

Please describe the bug

Operating system

Inko version