Arc Forum | Is sounds like most of what you're talking about is quasiquotation. (Maybe a laz...

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2 points by rocketnia 2062 days ago | link | parent

Is sounds like most of what you're talking about is quasiquotation. (Maybe a lazy quasiquotation?)

For this:

  (cons 1 (cons (car x) (cdr y)))

You're writing this:

  (1 (/ car x) / cdr y)

The same thing with quasiquotation would usually be:

  `(1 ,(car x) . ,(cdr y))

And that's sugar for this (possibly using different words on different Lisp dialects):

  (quasiquote (1 (unquote (car x)) . (unquote (cdr y))))

And then `quasiquote` itself is a macro. It's an interesting macro to implement, and I just spent like two years trying to streamline the way I was implementing it for my languages 'cause I kept adding bells and whistles to it. :)

If you write a slightly different macro where the syntax for (unquote ___) is (/ . ___), then you could use it like this, which matches the syntax of your example exactly:

  (t-expr (1 (/ car x) / cdr y))

I think the advantages of quasiquotation specifically shine when the quoted data is also program code in the same language (or like you just said, a DSL). In that specific case, I like that the code I'm writing looks the same regardless of whether it's under an unquote or not. There's a practical advantage in terms of being able to copy the code back and forth as necessary.

It sounds like you're looking at this as a data encoding? A lot of data encodings take pains not to be Turing-complete. Then again, for inexpressive languages like HTML, there are a lot of Turing-complete templating languages designed to dynamically generate them.

HTML has other languages embedded in it like JavaScript, and it sounds like that's relevant to what you're going for here. You're going for a language which can begin running even though not all the syntax is computed yet. That's pretty interesting. (Actually, maybe I'm projecting, 'cause I've been dreaming of something like that too: A language which multiple people collaborate on, which can begin running before all of the code has been written.)

You can of course experiment with that in most Lisp dialects using a quasiquoted term where all the unquotes have functions in them:

  (my-interpreter `(1 ,(lambda () (car x)) . ,(lambda (cdr y))))

And you could write a macro that puts in those lambdas automatically so it's not so verbose. Then your parser could use the Lisp's reader, wrap the result in (t-expr ...), and eval it in an appropriate namespace to yield your compiled program-syntax-with-functions-in-it. Then you could pass that syntax through an interpreter.

Is this all making sense? XD I started going through ideas a little fast, and maybe I missed your point a long time ago.