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2 points by aw 2826 days ago | link | parent

The second (if I'm not mistaken) is what you need for quasiquotation, but it would require introducing into the target environment a run-time dependency on LavaScript's eval. Am I making any sense?

Not sure :-) To put it in my own words, macros and quasiquotation are expanded at compile-time. Thus there is a compile-time dependency: in whatever language you write your macros in, you need to be able to be able to call functions written in that language from your compiler.

Take Arc as an example. A macro in Arc is an association between the macro name and a function that does the work of expanding the macro. Saying

  (mac foo ()
    `(+ 1 2))
is just a shortcut for this:

  (def expand-foo ()
    `(+ 1 2))
  (assign foo (annotate 'mac expand-foo))
now, I can write the "expand-foo" function in any language I want, as long as I can call it from the compiler. Here, I happen to have written it in Arc. But I could have written it in Scheme. Or, I could have written it in Javascript, if I had some way of calling Javascript from Arc, such as by shelling out to a Javascript interpreter. All "expand-foo" does is take one list and return another list, so I could write that in any language.

So, if you want to write full-strength macros in LavaScript, you need some way for your compiler to be able to call, during compilation, a function you've previously written in LavaScript.

Which, if LavaScript functions are compiled into Javascript, means if you can call Javascript functions from your compiler.

If you can do that, then you'll also get quasiquotation, because quasiquotation can be implemented as a macro.

If you can't call Javascript functions from your compiler, and if you want full-strength macros, then you'd need to write your macros in some language that you can call from your compiler.

3 points by aw 2825 days ago | link

Oh, I was confused:

The reason for not supporting eval is that this is a source-to-source compiler like CoffeeScript, not a run-time environment.

I wasn't paying attention and thought you meant LavaScript was written in CoffeeScript...

but I'm starting to doubt that this language can (or should) support full-fledged quasiquotation

I think I'm starting to get it: it's not that you couldn't support full-fledged quasiquotation if you wanted to by writing out an implementation in Javascript, it's that it wouldn't be very useful without being able to write macros via functions written in LavaScript, which in turn would mean that you'd have to be able to support loading LavaScript programs incrementally, which would mean having the LavaScript compiler in the runtime environment.


1 point by evanrmurphy 2825 days ago | link

Yes, I think that's right.