Using alias with effect parameter in type signature triggers internal error (kind mismatch)

[chtenb]

This compiles:

pub effect yield<a>
  ctl yield(elem : a) : ()
  
pub fun repeat(value : a) : (() -> <yield<a>,div> ())
  fun rec()
    yield(value)
    rec()
  rec

This does not:

pub alias stream<a,e> = () -> <yield<a>|e> ()

pub fun repeat(value : a) : stream<a,div>
  fun rec()
    yield(value)
    rec()
  rec

repro(1, 1): internal error: Type.TypeVar.subNew.KindMismatch: length 2: (19::KCon V |-> 63::KCon V)
(20::KCon E |-> std/core/types/div::KCon X)

CallStack (from HasCallStack):
  error, called at src\Common\Failure.hs:46:12 in koka-3.1.3-5fapaLngEoI9NoFrdTDxYE:Common.Failure
  raise, called at src\Common\Failure.hs:32:5 in koka-3.1.3-5fapaLngEoI9NoFrdTDxYE:Common.Failure
  failure, called at src\Common\Failure.hs:28:11 in koka-3.1.3-5fapaLngEoI9NoFrdTDxYE:Common.Failure
  assertion, called at src\Type\TypeVar.hs:163:9 in koka-3.1.3-5fapaLngEoI9NoFrdTDxYE:Type.TypeVar
  subNew, called at src\Kind\Infer.hs:1498:79 in koka-3.1.3-5fapaLngEoI9NoFrdTDxYE:Kind.Infer

Unless I'm missing something, I think the second snippet should compile as well, but otherwise this should give a normal error I think.

[TimWhiting]

Yeah, we should have a normal error here:
Change stream<a,div> to stream<a,<div>>. Anything that should unify with e in |e needs to be a full effect row - which could be itself polymorphic if you want. It can't be a single effect label.

[chtenb]

Ah, I never realised that <div> was something different than div. Thanks for pointing that out.

[TimWhiting]

Yeah, I think it confuses people because if you only have a single effect in a function type, you can omit the row angle brackets in the effect type - but that only works for function types, not anywhere else a row is expected.