Prexonite Script

The Philosophy Behind: The Prexonite Type System

This is the second article in the "Philosophy Behind"-series, picking up a specialty of one of my projects and explaining how it came to be made. Last time I wrote about the "auto dereferencing" concept in Prexonite Script.

In today's article I will explain the reasons behind the design of the Prexonite type system. Prexonite faces the same problem as other implementations of late-bound languages on the .NET platform: How to map the CTS to the language's type system.

I think the basic types Int32, Double, Boolean and String are more suited for a statically typed environment, so my type system must allow me to provide wrappers around third-party classes/structs. Wrapping and unwrapping objects must be as transparent as possible. Return values from base class library methods have to be wrapped in their Prexonite equivalent. At the same time, it is not practical to write a custom wrapper for every possible C# or VB.NET library, so there must be some sort of universal wrapper for CLR objects. With users of Prexonite being able to write their own wrappers, it must be possible to have multiple wrappers for the same CTS type. Also, some wrappers might handle more than one type.

The solution for Prexonite is the abstract class PType and some concrete subclasses, including the universal ObjectPType, which does all the late binding. Since Prexonite Script performs type checks at runtime, type information has to be associated with every data object, which is just what the class PValue does. What might surprise you, is the fact that Null is considered a type. Every null reference automatically has type Null.

Unlike the sturdy null references in C#, instances of Prexonite Null are completely functional objects. They react to operators, can be converted to basic values (Int, String,…) and even provide a ToString method. However, Null does have a special position in the Prexonite type system: it is not possible to write and use your own null reference wrapper.