Returning anonymous function does not always work

[chtenb]

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

This compiles without problems

However, returning an anonymous function instead, does not:

pub fun stream/repeat(value : a) : (() -> <div,yield<a>> ())
  fn()
    yield(value)
    stream/repeat(value)

repro.kk(16, 5): type error: types do not match
  context      : pub fun stream/repeat(value : a) : (() -> <div,yield<a>> ())
                 ...
                     stream/repeat(value)
  term         :     stream/repeat(value)
  inferred type: ()
  expected type: () -> <div,yield<_a>> ()
  because      : type cannot be instantiated to match the annotation

Why does this error occur only in the latter case?

[TimWhiting]

The problem here is that calling stream/repeat returns a function and you want to call it still.

Try this:

pub fun stream/repeat(value : a) : (() -> <div,yield<a>> ())
  fn()
    yield(value)
    stream/repeat(value)()

[chtenb]

Thanks, that makes sense. I don't know why this stumped me :)