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Interpretive systems are typically divided into a front end that parses the input language and produces an intermediate representation for the program, and an interpreter that executes the intermediate representation of the program.
For efficient interpreters the intermediate representation of choice is virtual machine code (rather than, e.g., an abstract syntax tree). Virtual machine (VM) code consists of VM instructions arranged sequentially in memory; they are executed in sequence by the VM interpreter, but VM branch instructions can change the control flow and are used for implementing control structures. The conceptual similarity to real machine code results in the name virtual machine. Various terms similar to terms for real machines are used; e.g., there are VM registers (like the instruction pointer and stack pointer(s)), and the VM instruction consists of an opcode and immediate arguments.
In this framework, Vmgen supports building the VM interpreter and any
other component dealing with VM instructions. It does not have any
support for the front end, apart from VM code generation support. The
front end can be implemented with classical compiler front-end
techniques, supported by tools like flex and bison.
The intermediate representation is usually just internal to the interpreter, but some systems also support saving it to a file, either as an image file, or in a full-blown linkable file format (e.g., JVM). Vmgen currently has no special support for such features, but the information in the instruction descriptions can be helpful, and we are open to feature requests and suggestions.