66 lines
3.1 KiB
Ruby
66 lines
3.1 KiB
Ruby
module Virtual
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# The Virtual Machine is a value based virtual machine in which ruby is implemented. While it is value based,
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# it resembles oo in basic ways of object encapsulation and method invokation, it is a "closed" / static sytem
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# in that all types are know and there is no dynamic dispatch (so we don't bite our tail here).
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#
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# It is minimal and realistic and low level
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# - minimal means that if one thing can be implemented by another, it is left out. This is quite the opposite from
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# ruby, which has several loops, many redundant if forms and the like.
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# - realistic means it is easy to implement on a 32 bit machine (arm) and possibly 64 bit. Memory access, a stack,
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# some registers of same size are the underlying hardware. (not ie byte machine)
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# - low level means it's basic instructions are realively easily implemented in a register machine. ie send is not
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# a an instruction but a function.
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#
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# So the memory model of the machine allows for indexed access into and "object" . A fixed number of objects exist
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# (ie garbage collection is reclaming, not destroying and recreating) although there may be a way to increase that number.
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#
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# The ast is transformed to virtaul-machine objects, some of which represent code, some data.
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#
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# The next step transforms to the register machine layer, which is what actually executes.
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#
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# More concretely, an virtual machine is a sort of oo turing machine, it has a current instruction, executes the
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# instructions, fetches the next one and so on.
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# Off course the instructions are not soo simple, but in oo terms quite so.
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#
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# The machine is virtual in the sense that it is completely
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# modeled in software, it's complete state explicitly available (not implicitly by walking stacks or something)
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# The machine has a no register, but local variables, a scope at each point in time.
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# Scope changes with calls and blocks, but is saved at each level. In terms of lower level implementation this means
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# that the the model is such that what is a variable in ruby, never ends up being just on the pysical stack.
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#
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class Machine
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# the main machine is the one that runs on the main thread, if it exists or receives an uncaught exception, that's it.
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def self.main
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@main || @main = Machine.new
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end
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def initialize
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# a binding represents the local variables at a point in the program.
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# The amount of local variables is assumed to be relatively small, and so the
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# storage is a linked list. Has the same api as a ha
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@bindings = List.new
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end
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attr_reader :bindings
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# run the instruction stream given. Instructions are a graph and executing means traversing it.
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# If there is no next instruction the machine stops
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def run instruction
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while instruction do
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next_instruction = instruction.next
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instruction.execute
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instruction = next_instruction
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end
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end
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end
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end
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require_relative "list"
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require_relative "instruction"
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require_relative "frame"
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require_relative "value"
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require_relative "mystery"
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require_relative "object"
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require_relative "constants"
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