Executing the Script

It is impossible to interpret an XPL script directly like in the first expression calculator example. It probably works also here, but only for expressions. Statements like while…do or if…else are not directly interpretable because they have a body and a conditional part. Because of that, we need to compile the program internally into a structure for a virtual machine. This virtual machine uses an assembly like command language, working with opcodes and operands.

The parser has the purpose to build up a cascading structure of nodes, which form the program that can be executed. This method avoids the use of dealing with jumps to addresses but cannot be used to write to a file.

Note that this compiler will not compile into an assembly code file. The assembly program is constructed directly into memory as an internal structure. The virtual machine executing this structure will at least have one function, which calls itself recursively based on the operation it should execute.