For a long time I'd been hoping to add a scripting language to LibQ, to use in any of my (or other people's) projects that needed a scripting language. The ideal scripting language would be well known, portable (that is, the interpreter code should be portable), flexible, and easy to interface with. However, just in the last couple days, I've come up with arguably my most insane idea ever for a programming project. While I don't think I'll discuss the idea here, let's say that one of the staples of this project would be LARGE scripts, making speed a requirement as well.
Given all these criteria, two languages jumped to mind: Java and C#. Both of these languages are well known (although Java significantly more than C#), flexible, portable (again Java more than C#), and fairly easy to interface with (C# more than Java, actually). You'll also notice that these are less than conventional choices for scripting languages... that is, they're NOT scripting languages, but rather compiled languages. This was how I thought would be the best way to meet the speed requirement, as they'll run circles around interpreted languages (probably at least 10x as fast).
So, first we examine Java. Java is perhaps the most well known programming language today (possibly second to C/C++), and Sun makes a virtual machine for all major OSs, as well as the minor OSs. Benchmarks I did a year or two ago showed that Java executed equivalent computational code at about half the speed of native code (that is, it took twice as long to execute). What I really didn't know is how easy it was to interface with. So, I looked up the Java Native Interface on Sun's Java site, and started playing. It turns out that it's quite easy to host a Java virtual machine and interact with it.
Benchmarks showed that it took about 450 cycles to call a native function from Java code, and about 3100 cycles to call a Java function from native code. 450 cycles isn't bad, but 3100 cycles is a bit slow (at least for said programming project). Also, there doesn't appear to be a programmatic interface to the Java compiler (Java code is compiled in two steps; first the source code is compiled to Java "machine language", and this code is what Java programs are usually distributed as; then, at run time, the Java machine language is compiled to true machine language for the machine the program is executed on). This might be okay for some things (i.e. game scripts, where the scripts could be distributed in compiled form), but it's not a good thing for simple scripts (i.e. batch files).
UPDATE: I could have sworn I fixed that "Java makes a virtual machine" mistake this morning, when I was proof-reading it...