Sample scala code with type constraints and kleisli composition

loans.scala

package net.debasishg.fin

import org.joda.time.DateTime

trait Account {
  def no: String
  def name: String
  def openedOn: DateTime
  def closedOn: Option[DateTime]
}

case class CheckingAccount(
  no: String, 
  name: String, 
  openedOn: DateTime, 
  closedOn: Option[DateTime]) extends Account

case class SavingsAccount(
  no: String, 
  name: String, 
  openedOn: DateTime, 
  rateOfInterest: BigDecimal,
  minBalance: BigDecimal,
  closedOn: Option[DateTime]) extends Account

case class LoanAccount(
  no: String, 
  name: String, 
  openedOn: DateTime, 
  rateOfInterest: Option[BigDecimal],
  emi: Option[BigDecimal],
  status: AccountStatus = Applied, 
  closedOn: Option[DateTime]) extends Account

sealed trait AccountStatus
case object Applied extends AccountStatus
case object Approved extends AccountStatus

case class Credentials(name: String, address: String, age: Int)

import scalaz._
import Scalaz._

trait LoanProcessing {
  def applyForLoan[A <: LoanAccount](name: String, dateOfApplication: DateTime): Kleisli[Option, Credentials, A]
  def approve[A <: LoanAccount](zone: String): Kleisli[Option, A, A]
  def finalizeEMI[A <: LoanAccount](tenure: Int): Kleisli[Option, A, A]

  def loanProcessing(name: String, dateOfApplication: DateTime, zone: String, tenure: Int) = 
    applyForLoan(name, dateOfApplication) >=> approve[LoanAccount](zone) >=> finalizeEMI(tenure)
}