TreeTransformScopeInstance

append cps tree, which is frs and then snd. we use this representation instead Mapped/Flatmapped in cases, where we later can apply await to append term and simplify tree instead wrapping awaited tree in extra flatMap

when we have swhifted function, which should return F[A] but we want to have in F[A] methods with special meaning, which should be performed on F[_] before jumping into monad (exampe: Iterable.withFilter) we will catch in ApplyTree such methods and substitute to appropriative calls of shifted.

represent select expression, which can be in monad or outside monad.

constructor is not devoted to used directly: use SelectTypeApplyCpsTree.create instead. selects is reversed (i.e. external added to head)

How to handle arguments? We want keep evaluation order from left to right, so, imagine we have function f(a1,a2,a3) and a2 is async, a1, a3 - sync. we will transform this to

{ val arg1 = a1;
  transform(a2).flatMap( x =>
     { val arg2 = x;
       val arg3 = a3;
       f(arg1, arg2, arg3)
}    }

more generally we at first generate block: { arg1 = a1; ..... argN = aN; f(arg1,...argN) } and then transform one, knowing that all arguments to f are sync (of course, if all arguments are sync, we just call f(arg1,... arg2) without all this machinery)

applyTerm = Apply(fun, args) fun = TypeApply(obj,targs)

case Apply(fun,args) transform application

tails -- list of prepared sequence of curried arguments.