Overview

gmStudio is a platform for building VB6/ASP upgrade solutions that meet real-world requirements. Initially, the platform offered two ways that developers could customize how it works:

• gmPL Scripts using an XML-like notation to implement declarative specifications that direct and inform the translation engine's operation

• gmSL Scripts using a C-like notation to implement classes, methods, and event handlers that can extend the translation engine's operation

gmPL and gmSL provide a great deal of expressive power and precision. For example, we built several advanced COM API migrations, and a VB6 Forms to WPF/XAML extension using gmSL. Many gmPL and gmSL files are included in the standard gmStudio distribution and others are available for download from this documentation portal. But, they have their limitations. For example, gmSL lacked a contemporary development support (i.e. no intellisense and no debugger).

In early 2018, during the course of planning a big VB6-to-WPF project, the customer asked if they could use a C# API instead of gmSL language for their WPF migration and gmAPI was born. gmAPI is a powerful alternative to gmSL. gmAPI can access even more system services than gmSL, but gmAPI logic is developed in C# (of VBNET) so it enjoys all of the benefits of being part of the .NET ecosystem such as using a contemporary IDE, being a fully compiled language, interactive debugging, .NET framework services and tools, etc.

The introduction of gmPL Extensions makes integrating gmAPI logic with the translation engine more robust and seamless. gmPL Extensions define the conventions for defining new gmPL language elements and integrating gmAPI assemblies with the core translation engine. gmPL Extensions extend the set of gmPL statements that are recognized and processed by the gmStudio platform allowing motivated users to develop the code analysis and transformation features they need.

gmPL Extension dll Resolution and Invocation

When gmBasic is processing a gmPL script and it encounters a script statement that it does not recognize, it looks for a .NET assembly named "gmPL_(%statement%).dll". If the dll is found, gmBasic looks for a class "gBasicMain.gmPL_(%statement%)". If that class can be instantiated, the resulting instance is used to invoke a method named XeqStatement to handle the extended command.

The process for finding the extension DLL first looks in the folder containing gmBasic. This is used for the gmPL dlls in the gmStudio distribution.For example, the extension tag below will engage extension code in gmPL_GlobalStubs.dll located in the same folder as gmBasic.exe.