ruby-x.github.io/app/views/pages/rubyx/layers.html.haml

= render "pages/rubyx/menu"

%h1=title "RubyX architectural layers"
%p
  To implement an object system to execute object oriented languages takes a large system.
  The parts or abstraction layers are detailed below.
%p
  It is important to understand the approach first though, as it differs from the normal
  interpretation. The idea is to
  %strong compile
  ruby. The argument is often made that
  typed languages are faster, but i don’t believe in that. I think dynamic languages
  just push more functionality into the “virtual machine” and it is in fact only the
  compiling to binaries that gives static languages their speed. This is the reason
  to compile ruby.
%p.center
  = image_tag "layers.jpg" ,  alt: "Architectural layers"

%h3#ruby Ruby
%p
  To compile and run ruby, we first need to parse ruby. While parsing ruby is quite
  a difficult task, it has already been implemented in pure ruby
  = succeed "." do
    =ext_link "here" ,"https://github.com/whitequark/parser"
  The output of the parser is
  an ast, which holds information about the code in instances of a single
  %em Node
  class.
  Nodes have a type attribute (which you sometimes see in s-expressions) and a list of children.
%p There are two basic problems when working with ruby ast: one is the a in ast, the other is ruby.
%p
  Since an abstract syntax tree only has one base class, one needs to employ the visitor
  pattern to write a compiler. This ends up being one great class with lots of unrelated
  functions, removing much of the benefit of OO.
%p
  The second, possibly bigger problem, is ruby itself: Ruby is full of programmer happiness,
  three ways to do this, five to do that. To simplify that, remove the duplication and
  make analyis easier, Vool was created.

%h3#virtual-object-oriented-language Virtual Object Oriented Language
%p
  Virtual, in this context, means that there is no syntax for this language; it is an
  intermediate representation which
  %em could
  be targeted by several real languages.
%p
  The main purpose is to simplify existing oo languages down to it’s core components: mostly
  calling, assignment, continuations and exceptions. Typed classes for each language construct
  exist and make it easier to transform a statement into a lower level representations.
%p
  Examples for things that exist in ruby but are broken down in Vool are
  %em unless
  ,
  %em ternary operator
  ,
  %em do while
  or
  %em for
  loops and other similar syntactic sugar.

%h3#minimal-object-machine Minimal Object machine
%p
  We compile Vool statements into Mom instructions. Mom is a machine, which means it has
  instructions. But unlike a cpu (or the risc layer below) it does not have memory, only objects.
  It also has no registers, and together these two things mean that all information is stored in
  objects. Also the calling convention is object based and uses Frame and Message instances to
  save state.
%p
  Objects are typed, and are in fact the same objects the language operates on. Just the
  functionality is expressed through instructions. Methods are in fact defined (as vool) on classes
  and then compiled to Mom/Risc/Arm and the results stored in the method object.
%p
  The Mom level exists to make the transition to Risc easier. It has a very abstract,
  high level instruction set, where each single instruction may resolve to many tens
  of lower level instructions. But it breaks down Vool's tree into an instruction
  list, which is conceptually a much easier input for the next layer.

%h3#risc Risc
%p
  The Register machine layer is a relatively close abstraction of risc hardware, but without the
  quirks.
%p
  The Risc machine has registers, indexed addressing, operators, branches and everything
  needed to implement Mom. It does not try to abstract every possible machine feature
  (like llvm), but rather “objectifies” the general risc view to provide what is needed for
  the Mom layer, the next layer up.
%p
  The machine has it’s own (abstract) instruction set, and the mapping to arm is quite
  straightforward. Since the instruction set is implemented as derived classes, additional
  instructions may be defined and used later, as long as translation is provided for them too.
  In other words the instruction set is extensible (unlike cpu instruction sets).
%p
  Basic object oriented concepts are needed already at this level, to be able to generate a whole
  self contained system. Ie what an object is, a class, a method etc. This minimal runtime is called
  parfait, and the same objects will be used at runtime and compile time.
%p
  Since working with at this low machine level (essentially assembler) is not easy to follow for
  everyone (me :-), an interpreter was created (by me:-). Later a graphical interface, a kind of
  %a{:href => "https://github.com/ruby-x/rubyx-debugger"} visual debugger
  was added.
  Visualizing the control flow and being able to see values updated immediately helped
  tremendously in creating this layer. And the interpreter helps in testing, ie keeping it
  working in the face of developer change.

%h3#binary--arm-and-elf Binary , Arm and Elf
%p
  A physical machine will run binaries containing instructions that the cpu understands, in a
  format the operating system understands (elf). Arm and elf subdirectories hold the code for
  these layers.
%p
  Arm is a risc architecture, but anyone who knows it will attest, with it’s own quirks.
  For example any instruction may be executed conditionally, ie
  %em every
  instruction carries bits to make it check the status register. Or the fact that there
  is no 32bit register load instruction. It is possible to create very dense code using
  all the arm special features, but this is not implemented yet.
%p
  The Arm::Translator translates that translates RegisterInstructions to ArmInstructions,
  and the Elf::ObjectWriter creates Linux binaries.