sorting - scala parameterised merge sort - confusing error message -

i getting compilation error when calling (lt: (t,t) => boolean) function
error code "type mismatch; found : x.type (with underlying type t) required: t"
, x parameter in lt(x,y) underlined.

object sort {   def msort[t](xs: list[t])(lt: (t, t) => boolean): list[t] = {     def merge[t](xs: list[t], ys: list[t]): list[t] = (xs, ys) match {       case (nil, ys) => ys       case (xs, nil) => xs       case (x :: xs1, y :: ys1) => {         if (lt(x, y)) x :: merge(xs1, ys)         else y :: merge(xs, ys1)       }     }      val n = xs.length / 2     if (n == 0) xs     else {       val (left, right) = xs splitat n       merge(msort(left)(lt), msort(right)(lt))     }   } } 

msort , merge have different type parameters. remove t type parameter merge:

def merge(xs: list[t], ys: list[t]): list[t] = (xs, ys) match { 

the [t] declares new parameter unrelated first. same error if declare as:

def merge[u](xs: list[u], ys: list[u]): list[u] = (xs, ys) match { 

lt has type (u, u) => boolean, , you're calling x , y have type t , don't match.