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2 points by joshudson 4120 days ago | link | parent

OK, this might be a stupid question.

Is there any hope of getting arc2c able to compile itself anytime soon? This is exactly what you would need for a self-hosting arc environment. -JH

Yes, I'm new here.



1 point by almkglor 4120 days ago | link

None yet. What's currently blocking us badly is handling macros in the code for compilation. Like any decent Lisp program, arc2c makes quite a bit of use of macros.

Unfortunately macros require us to embed an Arc interpreter in the compiler itself, and we can't use the builtin 'eval because we don't want the macros under compilation to accidentally bash global functions/variables used by the compiler itself.

You'll have to contact sacado if you're interested in chipping in, we haven't figured out how to make a git on github publicly pushable.

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1 point by sacado 4120 days ago | link

As almkglor said, macros are the real problem as for now. Once we will have them working, a meta-circuar arc2c should be straightforward.

We will need 'read and 'eval functions (that should be easy, and they will probably have to be fully operational for macros anyway) and error handling (a trivial error handling, sufficient for arc2c's code, could be easily implemented : just write an error message and exit). A poor, but meta-circular compiler. Then, we'll have to optimize / improve everything left.

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2 points by almkglor 4120 days ago | link

Re: eval - We need a way to implement 'apply.

It's not easy. We can't make it into a primitive, because CPS conversion assumes that primitives will never need access to continuations, and thus does not transform primitive calls to CPS form.

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1 point by sacado 4119 days ago | link

Couldn't it be implemented as :

- PUSH the closure to be called

- PUSH the list of args

- call the APPLY() function, which just POPs the two elements, PUSHes all the elements of the arg list one after one, then call the closure (maybe after changing the continuation argument of that closure by hand, at runtime) ?

That's a runtime behavior, for sure, and probably a few cases should be hard-coded in the generated C file. E.g., (apply + '(1 2)) should be translated to (+ 1 2), then to 3, if nothing bad (redefinition of '+ or 'apply by the user) happened. But in the general case, you can't know.

Anyway, we will eventually have to implement an interpreter in the generated code, to deal with dynamic stuff. Maybe closures should be made available through a hashtable mapping their name(s) to actual code, and not only through a hard-coded array as it is now ?

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1 point by almkglor 4118 days ago | link

> Couldn't it be implemented as :

> - PUSH the closure to be called

> - PUSH the list of args

> - call the APPLY() function, which just POPs the two elements, PUSHes all the elements of the arg list one after one, then call the closure (maybe after changing the continuation argument of that closure by hand, at runtime) ?

Which continuation argument do you pass?

Suppose it's like this:

  (%car (%apply foo bar))
Then foo is:

  (set foo
    (fn (a b)
      (ccc
        (fn (k)
          (a k b)))))
Question: How does '%apply get access to the continuation, in order to pass to 'foo, which passes it to 'ccc ?

Remember, calling a function consists of the following steps:

1. Push the closure

2. Push the continuation

3. Push the arguments

The problem is step 2: continuation.

Possibly we need to insert the default 'apply during the same step as inserting the default 'ccc ? Then we could define '%apply as accepting the function, the continuation, and a plain list of arguments.

> Anyway, we will eventually have to implement an interpreter in the generated code, to deal with dynamic stuff. Maybe closures should be made available through a hashtable mapping their name(s) to actual code, and not only through a hard-coded array as it is now ?

s/closure/global variable/, maybe?

I think what we could do is, we add a pointer to an obj in the symbol structure. If the symbol is in the GLOBAL() array, this pointer points to that entry, otherwise to a malloc()'ed location.

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1 point by sacado 4119 days ago | link

oh, yes, 'apply & CPS... Well, I'll have a look at that today. I'll see if I can work around it.

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