scalacheck - Type mismatch error in a scala for comprehension -

i writing generators following adts. idea generate blocks random data. having compiler error type mismatch: expected: seq[field], actual:gen[field] in blockgen method. doing wrong?

edit

the error fields on last line of method i.e. yield block(id, fields).

def blockgen(b: block): gen[block] = {     id <- b.blockid     fields <- b.fields.map(f => fieldgen(f)) } yield block(id, fields) 

adt

trait data {}  trait field extends data {   val name: string   val value: string }  case class stringfield(name: string, value: string) extends field case class numberfield(name: string, value: string) extends field case class block(blockid: field, fields: seq[field]) extends data 

generators

def blockgen(b: block): gen[block] = {     id <- b.blockid     fields <- b.fields.map(f => fieldgen(f))   } yield block(id, fields)  def fieldgen(fieldtype: field): gen[field] = {     {       f <-       fieldtype match {         case _: numberfield => numgen         case _: stringfield => strgen       }     } yield f   }  val strgen: gen[stringfield] = {     name <- gen.identifier     value <- gen.alphastr   } yield stringfield(name, value)  val numgen: gen[numberfield] = {     name <- gen.identifier     value <- gen.numstr   } yield numberfield(name, value) 

this caused by: fieldgen(f) return type gen[field], block fields type seq[field], compiler throw type mismatch.

solution:

1. change def fieldgen(fieldtype: field): gen[field] def fieldgen(fieldtype: field): seq[field], or change block fields type gen[feild]

2. create implicit conversion gen seq, like:

   implicit def gentoseq[t](s: gen[t]): seq[t] = ??? // implementation conversion.