Lift + Scala, Introduction

A recent show of Floss Weekly made me curious about Lift, a web framework using Scala.  

“Scala is a general purpose programming language designed to express common programming patterns in a concise, elegant, and type-safe way.” so they promise  on the Scala website.

The Lift project leader praises his product as “a concise language, frame work with security features, very performant...”

A first glance

Lift, like any framework that you haven't written yourself, will take some time getting familiar with, and Scala, well, it's just another computer language... or so I thought.

Lift

Perhaps the most important feature of Lift is its template system.  These templates are strictly XML based text files without any programming logic.  Tags within the template link to functions in your Scala code that generates some output.  This output (also XML) then replaces the tag.  After a few more processing steps the result is returned to the enquiring web browser, your page gets rendered, end of story.  Yes, there are lots of support features within the framework – like html form generation, database connectivity, page access control – but this is the basic principle of Lift.

Scala

The designers of Scala cherry-picked the best features and concepts from other programming languages, some object-oriented stuff but they also borrowed heavily from functional programming. Its mantra: “everything is an object” and “if it's worth saying, say it with a function”.

Scala's smart compiler can in most cases infer types of variables, so you don't have to declare it manually.  The language has lots of these simplyfications, dramatical reducing boiler plate code.  However, you have to be familiar with these in order to be able to revert the expression back to its more verbose form, otherwise you will scratch your head when you encounter the “Scala smiley”:

 ( _ + _ )

Some language constructs help you avoiding Null pointer dereferences, or to catch all possible cases in a matching construct.  And being a statically typed language  the Scala compiler will be very stubborn if your types don't match.

You can write very elegant code – even though I wouldn't call deeply nested function calls simple to read, at least not yet.

Treacherous simplicity

Letting the compiler infer types looks like a good idea.  On second sight, it also means that you need a good memory or at least a helpful IDE.

Simplifying

   val a: Int = 1

to

   val a = 1

is simple and easy to understand. (The literal 1 is an integer, i.e. “a” must be integer as well). But:

val a = function_i_wrote_ealier_and_dont_remember_the_return_type()
val b = another_cool_function_from_the_web_framework(User => go look)

does work just as well. And now you either know the types or you have to look it up.

The possibility to drop dots and brackets in some situation lets you further “simplify” things:

   a.+(b)

becomes a much more friendlier

   a + b

(+ is a valid function name in Scala).

But

   a :: b

does not mean

   a.::(b)

but

   b.::(a)

(“Operators” that end with “:” bind from right to left).

Another nice feature: When defining a class how often have you assigned the values from the constructor parameter list to class variables for later use? It's usually the first thing you do.  In Scala this is done automatically.  Why hasn't somebody invented this earlier? 

Documentation + support

There is documentation available for Lift and Scala on the web.  While perhaps not exactly light reading, they will get you started.

For Scala http://programming-scala.labs.oreilly.com/index.html from O'Reilly is a good start, and on the Scala website there is http://www.scala-lang.org/docu/files/ScalaByExample.pdf.  Both publications expect that you have done some programming before.

For Lift you should check out master.pdf from http://groups.google.com/group/the-lift-book/files. More information is available at the Lift Wiki and a subscription to the Lift newsgroup is also recommended.