scala - Constructing TypeTags of higher-kinded types -

given simple parametrized type class lk[a], can write

// or simpler def taglk[a: typetag] = typetag[lk[a]] def taglk[a](implicit ta: typetag[a]) = typetag[lk[a]]  taglk[int] == typetag[lk[int]] // true 

now i'd write analogue class hk[f[_], a]:

def taghk[f[_], a](implicit ???) = typetag[hk[f, a]]  // or other implementation?  taghk[option, int] == typetag[hk[option, int]] 

is possible? i've tried

def taghk[f[_], a](implicit tf: typetag[f[_]], ta: typetag[a]) = typetag[hk[f, a]]  def taghk[f[_], a](implicit tf: typetag[f], ta: typetag[a]) = typetag[hk[f, a]] 

but neither works obvious reasons (in first case f[_] existential type instead of higher-kinded one, in second typetag[f] doesn't compile).

i suspect answer "it's impossible", happy if isn't.

edit: use weaktypetags follows (slightly simplified):

trait element[a] {   val tag: weaktypetag[a]   // other irrelevant methods }  // e.g. def seqelement[a: element]: element[seq[a]] = new element[seq[a]] {   val tag = {     implicit val ta = implicitly[element[a]].tag     weaktypetag[seq[a]]   } }  trait container[f[_]] {   def lift[a: element]: element[f[a]]    // note bound satisfied, pass    // tag explicitly when used   def tag[a: weaktypetag]: weaktypetag[f[a]] }  val seqcontainer: container[seq] = new container[seq] {   def lift[a: element] = seqelement[a] } 

all of works fine if replace weaktypetag typetag. unfortunately, doesn't:

class free[f[_]: container, a: element]  def freeelement[f[_]: container, a: element] {   val tag = {     implicit val ta = implicitly[element[a]].tag     // need typetag[f] here     // obtained implicit container[f]     typetag[free[f, a]]   } } 

does serve purposes?

def taghk[f[_], a](implicit tt: typetag[hk[f, a]]) = tt 

as opposed using implicit parameter typetag f , a separately , composing them, can directly request tag want compiler. passes test case desired:

taghk[option, int] == typetag[hk[option, int]] //true 

alternatively, if have instance of typetag[a] try:

object hk {     def apply[f[_]] = new hktypeprovider[f]     class hktypeprovider[f[_]] {         def get[a](tt: typetag[a])(implicit hktt: typetag[hk[f, a]]) = hktt     } } 

allowing do:

val mytt = typetag[int] hk[option].get(mytt) == typetag[hk[option, int]] //true