gistfile1.scala

// validate trade quantity
def validQuantity(qty: BigDecimal): Validation[String, BigDecimal] = 
  try {
    if (qty <= 0) "qty must be > 0".fail
    else if (qty > 500) "qty must be <= 500".fail
    else qty.success
  } catch {
    case e => e.toString.fail
  }

// validate unit price
def validUnitPrice(price: BigDecimal): Validation[String, BigDecimal] = 
  try {
    if (price <= 0) "price must be > 0".fail
    else if (price > 100) "price must be <= 100".fail
    else price.success
  } catch {
    case e => e.toString.fail
  }

// make a trade or report validation failures
def makeTrade(account: Account, instrument: Instrument, refNo: String, market: Market, 
  unitPrice: BigDecimal, quantity: BigDecimal) =
  (validUnitPrice(unitPrice).liftFailNel |@| 
    validQuantity(quantity).liftFailNel) { (u, q) => Trade(account, instrument, refNo, market, u, q) }