scala - How to create a generic Monoid from an ADT -


given have existing adt, possible create generic monoid.

from now, have many monoid classes in adt, it's not dry.

here code :

import scalaz._ import scalaz._  object datarework extends app {   sealed trait multiitemvalue {     type mv     def value: seq[mv]   }    case class stringvalue(value: seq[string]) extends multiitemvalue{type mv = string}   case class booleanvalue(value: seq[boolean]) extends multiitemvalue{type mv = boolean}    implicit object booleanvaluemonoid extends monoid[booleanvalue] {     override def zero: booleanvalue = booleanvalue(nil)     override def append(f1: booleanvalue, f2: => booleanvalue): booleanvalue = booleanvalue(f1.value ++ f2.value)   }    implicit object stringvaluemonoid extends monoid[stringvalue] {     override def zero: stringvalue = stringvalue(nil)     override def append(f1: stringvalue, f2: => stringvalue): stringvalue = stringvalue(f1.value ++ f2.value)   }

i like, found code ugly due repetition :

  implicit object genericmonoid extends monoid[multiitemvalue] {     override def zero: multiitemvalue = ???     override def append(f1: multiitemvalue, f2: => multiitemvalue): multiitemvalue = (f1, f2) match {       case (sv1: stringvalue, sv2: stringvalue) => stringvalue(sv1.value ++ sv2.value)       case (bv1: booleanvalue, bv2: booleanvalue) => booleanvalue(bv1.value ++ bv2.value)     }   }


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