If performance is a concern, then you need learn C. Along with it, you learn the fundamental knowledge of how computer program works, which will benefit on all level of programming.
MyDef has massive support for C. Unlike perl module, MyDef's C module can manage functions and variables to achieve higher level syntaxes.
At this point, I like to re-iterate that, although MyDef will provide many features that you will love, there is no need to wait until you mastered all the features before you start to use it. Because MyDef works at semantic layer and takes in conventions to promote efficiency, the features MyDef includes will be ever-growing and even unstable -- just like our natural language. And just as we never wait for the whole vocabulary before we start to use it in daily communication, readers should avoid trying to master all the features listed in this book (and many not in this book) before start use it. Only through daily usage, you will understand, get used to, and become a true master.
For example, the feature this section is about to introduce, function is quite important for writing MyDef C code, but you can already write MyDef C by simply use plain C syntax to define C function. Of course, once you appreciated the new feature, you would like to rewrite all you code using the new feature. That is OK. You'll take joy in that refactoring.
Also remember, MyDef is simply a semantic layer. If you have certain production code in MyDef and is concerned with feature breakage, you could simply take the MyDef compiled source code and freeze that code. The underlying programming language is built for accuracy, and will ensure the stability of your production code. Or you can fork the current MyDef repository as a snapshot bound to your production code so you can ensure stability. MyDef installation procedures are designed with this practice in mind.