<Why does `EffectScope.shift` need the type parame...

# stackoverflow

[user]

Why does `EffectScope.shift` need the type parameter `B`?
The move to the new continuations API in Arrow brought with it a handy new function: shift, in theory letting me get rid of ensure(false) { NewError() } or NewError().left().bind() constructs.
But I'm not sure how to properly use it. The documentation states that it is intended to short-circuit the continuation, and there are no conditionals, so it should always take the parameter, and (in either parlance) "make it a left value", and exit the scope.
So what is the type parameter B intended to...