I’ve written one or two small pieces of software in the new upstart programming language Scala, and I love it. It takes all of what is good and right about Java and C#, removes a lot of the cruft, and introduces powerful new bits from modern functional languages. It’s a pleasure to write in.

Unfortunately there is one of the bits of cruft from C#/Java which is still there: the concept of ‘null’—a value which can legally be assigned to any reference type, but which causes an exception if you try to dereference it. It’s an ugly carbuncle on the type system, but, for compatability reasons, it’s never yet been removed.

Here I present one way of ridding the Scala world of nulls—whilst remaining compatible and efficient. I wish for World Peace and for this to be implemented in Scala 3…

[If you don’t care about programming, type systems and language implementation, I heartily suggest you skip this article. I’ll review a film soon. Promise.]

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I describe a technique in the C# language, and very small supporting library (hence ‘micro-framework’), for implementing business-logic–level tests which may be either short-cut evaluated (when you require a boolean yes/no), or fully evaluated (when you requite a list of ‘reasons why not’).

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Part III in a series of… some.

Part I covers static type checking in views and Why This Would Be Good.
Part II is about making the view architecture more naturally composable.
Part III, this article, is more narrowly concerned with return types from actions.

RenderView, Redirect and Friends

In MonoRail, ‘actions’ are the units of code which respond to an incoming page request, perform some work, then cause a view to be rendered or send a ‘redirect’—or potentially an error code—back to the client.

Actions are represented by methods on controller classes and are defined as returning ‘void’. Actions invoke a view or a redirect by calling other methods on the controller, RenderView, RedirectToAction, RedirectToUrl… and others. By default (if none of these is called) the framework will act as if the view has called RenderView(name-of-action). The parameters to the view must be placed in a global variable called PropertyBag.

This all to me seems quite unnatural.
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Part II in a series of… several.

In Part I I whined on about static type checking in views. Here I moan about composability of page elements.

Composability of Page Elements

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In work, we’ve been using MonoRail for a while. It’s a C#/.NET web application framework, and it’s very much nicer than ASP.NET, which is what I was using before.

Now I’ve had a bit of experience with it, though, there are things I would definitely change: I want the framework to allow me to compose page elements more easily, and to have stronger type-checking.

The easy one first. I’m going to talk about…

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