Explanation for parameterised handlers

[wongjiahau]

I came across the following phrase when reading Type Directed Compilation of Row-typed Algebraic Effects.

To define the state effect we could use the built-in state effect of Koka, but a cleaner way is to use parameterized handlers.
Such handlers take a parameter that is updated at every resume. Here is a possible definition for handling state:

val state = handler(s) { 
  return x → (x,s)
  get() → resume(s,s) 
  put(s’) → resume(s’,())
}

I tried to look for parameterized handler in Koka's documentation but there's no such references.

Is this feature removed from Koka? If not how it works?