Scala XHTML

I write web applications in Scala using its XML-literal support. This provides me the advantage of a statically-typed language while rendering templates.

Sometimes objections are raised. I will not address the most common of these objections in any detail. However, I will say that if you read a book on MVC and believe you are “separating concerns”, then you have been misguided. I have touched on the thesis of functional programming before, which provides composition in its true sense. I recommend Why Functional Programming Matters by John Hughes to get started on obtaining a true understanding of so-called separating concerns. Moving on…

I will present a trivial example of rendering objects in XHTML. Suppose we are building a criminology database which currently has two people in it.

val persons = List(
    Person("Fred Bloggs",
           "111 That Street Knobville",
           "12345678",
           "Knobs Inc.",
           Set(Stalking, SexualHarassment)),
    Person("Anthony McCrary",
           "31291 Tecla Drive Warren Michigan 48088",
           "5869447833",
           "l33t labs",
           Set(Stalking, PhoneHarassment))
  )

Then we wish to render these in an XHTML table — let’s ignore the objections to using tables for now.

def personsTable =
<table border="1">
  <tr>
    <th>Name</th>
    <th>Address</th>
    <th>Phone</th>
    <th>Employer</th>
    <th>Offences</th>
  </tr>
  {
    persons map (p => <tr>{
                        <td>{ p.name }</td>
                        <td>{ p.address }</td>
                        <td>{ p.phone }</td>
                        <td>{ p.employer }</td>
                        <td>{ p.offences.mkString(", ") }</td>
                     }</tr>)
  }
</table>

In a templating language we might use a loop and have limited library access without any checking. Unfortunately, your favourite HTML editor will not allow this method of development. There is a way to accommodate this. I will expand on it in the next post.

Here is a full compilable and executable source file:

case class Person(name: String, address: String, phone: String, employer: String, offences: Set[Offence])

sealed trait Offence
case object Stalking extends Offence
case object PhoneHarassment extends Offence
case object SexualHarassment extends Offence

object P {
  val persons = List(
    Person("Fred Bloggs",
           "111 That Street Knobville",
           "12345678",
           "Knobs Inc.",
           Set(Stalking, SexualHarassment)),
    Person("Anthony McCrary",
           "31291 Tecla Drive Warren Michigan 48088",
           "5869447833",
           "l33t labs",
           Set(Stalking, PhoneHarassment))
  )

def personsTable =
<table border="1">
  <tr>
    <th>Name</th>
    <th>Address</th>
    <th>Phone</th>
    <th>Employer</th>
    <th>Offences</th>
  </tr>
  {
    persons map (p => <tr>{
                        <td>{ p.name }</td>
                        <td>{ p.address }</td>
                        <td>{ p.phone }</td>
                        <td>{ p.employer }</td>
                        <td>{ p.offences.mkString(", ") }</td>
                     }</tr>)
  }
</table>

  def main(args: Array[String]) {
    println(personsTable)
  }
}

Here is how the output renders:

Name	Address	Phone	Employer	Offences
Fred Bloggs	111 That Street Knobville	12345678	Knobs Inc.	Stalking, SexualHarassment
Anthony McCrary	31291 Tecla Drive Warren Michigan 48088	5869447833	l33t labs	Stalking, PhoneHarassment

Please ask questions if you have any.