45 lines
2.1 KiB
Markdown
45 lines
2.1 KiB
Markdown
### Parfait: a thin layer
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Parfait is the run-time of the vm.
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To be more precise, it is that part of the run-time that can be expressed in ruby.
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The run-time needs to contain quite a lot of functionality for a dynamic system.
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And a large part of that functionality must actually be used at compile time too.
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We reuse the Parfait code at compile-time, by inlining it.
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A work in progress that started from here : http://salama.github.io/2014/06/10/more-clarity.html went on here
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http://salama.github.io/2014/07/05/layers-vs-passes.html
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A step back: the code (program) we compile runs at run - time.
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And so does parfait. So all we have to do is compile it with the program.
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And thus parfait can be used at run-time.
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It's too simple: just slips off the mind like a fish into water.
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Parfait has a brother, the Builtin module. Builtin contains everything that can not be coded in ruby,
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but we stil need (things like array access).
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#### Example: Message send
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It felt a little stupid that it took me so long to notice that sending a message is very closely related to the
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existing ruby method Object.send
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Off course Object.send takes symbol and the arguments and has the receiver, so all the elements of our
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Messaage are there. And the process that Object.send needs to do is exactly that:
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send that message, ie find the correct method according to the old walk up the inheritance tree rules and dispatch it.
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And as all this happens at runtime, "all" we have to do is code this logic. And since it is at runtime,
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we can do it in ruby (as i said, this get's compiled and run, just like the program).
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But what about the infinite loop problem:
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There was a little step left out: Off course the method gets compiled at compile-time and so
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we don't just blindly dispatch: we catch the simple cases that we know about:
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layout, type instance variables and compile time known functions.
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Part of those are some that we just don't allow to be overridden.
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Also what in ruby is object.send is Message.send in salama, as it is the message we are sending and
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which defines all the data we need (not the object). The object receives, it does not send.
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