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2 points by absz 5999 days ago | link | parent

This is actually also the million-dollar semantic question. Right now, arc-eval is not inserted around function or macro bodies, so only top-level forms (those at the repl) are affected. But we can't insert it around bodies as is, because (1) Arc-side eval doesn't take an environment, but they need to pass an environment in, and (2) they don't evaluate things immediately, but instead they create the forms that will be evaluated. What is the best way to do things here? We have no other language to guide us, after all.


2 points by skenney26 5999 days ago | link

I'm curious: So arc-eval translates your arc code into scheme code and then passes it to scheme's eval? If so, would it be possible to print the scheme code to a file before it gets evaluated?

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1 point by almkglor 5998 days ago | link

> I'm curious: So arc-eval translates your arc code into scheme code and then passes it to scheme's eval?

Yes, I think so.

> If so, would it be possible to print the scheme code to a file before it gets evaluated?

Yes. sacado did some work on this I think.

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1 point by almkglor 5998 days ago | link

Personally, I'm rather squeamish about letting 'eval be redefined. Because the redefined 'eval will not be consistently used.

Perhaps it's better to just define a top-level which preprocesses the code before passing it to 'eval?

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2 points by eds 5998 days ago | link

That could be accomplished by redefining 'arc-eval rather than 'eval. 'arc-eval is used internally for evaluating top-level forms but not really anything else since it isn't exposed to arc, whereas 'eval could be used by arbitrary arc code. If you want to redefine the top-level evaluation function, than maybe what you want is some way to influence the results of 'arc-eval.

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1 point by almkglor 5998 days ago | link

So much easier:

  (def mytl ()
    (pr "arc> ")
    (eval (my-transformation (read)))
    (mytl))

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2 points by eds 5998 days ago | link

I guess I misunderstood your intention. I thought you wanted to be able to redefine the existing toplevel used by the arc interpreter itself, not define a completely new toplevel to be used in user code... (and yes, the latter is quite trivial).

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1 point by almkglor 5998 days ago | link

> I thought you wanted to be able to redefine the existing toplevel used by the arc interpreter itself

As opposed to emulating the existing toplevel in user code?

Allowing a redefinition of 'eval to work on the REPL will probably be OK, but still, there would be an impedance mismatch with functions that were defined before 'eval was redefined.

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