Editing Yhc/RTS/Machine (section)

== Registers ==

The stack machine uses 'registers' (i.e. C variables) to store important information about the running state of the machine (see src/runtime/BCKernel/mutator.c).

The stack machine works by evaluating application nodes. Application nodes are calls to a given function with a given set of arguments. At any one time some application node (and thus some function) is 'currently under evaluation'. When a function is called it executes the bytecode instructions in that function which might cause the further evaluation of more application nodes. Eventually an application will produce a result and evaluation of an earlier application will continue.

The registers used in this process are:
* The instruction pointer (ip) points to current instruction being executed.
* The stack pointer (sp) points to the item on the top of the stack.
* The frame pointer (fp) points to the top frame on the stack.
* The heap pointer (hp) points to the start of free space in the heap.
* The vector application pointer (vapptr) points to the application node in the heap that is currently being evaluated.
* The const table pointer (constptr) points to the constant table of the current application node (vapptr).