I was thinking about adding "(and translation)" to that sentence, but I thought that was the easy part. After all, you can just write an interpreter that compiles to the lower level language and package it up with every Eight program. It isn't an especially insightful translation, perhaps, but it's a start.
Speaking of partial evaluators... I was thinking about this topic some more yesterday, in regards to my everything-is-a-multimethod language idea, and I came up with this. I imagine having
(aif a b c d e)
translate something like this:
(%apply %compile-to-apply '(aif a b c d e))
Here, %apply is a special value that the compiler knows will evaluate all its parameters, then apply the first parameter to the next. Meanwhile, %compile-to-apply actually breaks down the syntax passed to it so that there's a simpler %apply to execute. Since %apply, %compile-to-apply, and '(aif a b c d e) are constants, a partial evaluator can simplify this to:
(%apply (%compiler-of aif) '(a b c d e))
Here, %compiler-of is yet another compiler-internal procedure that looks at the signature of its argument in order to produce another procedure that does the actual work of compiling a parameter list to a simpler %apply form. Since (%compiler-of aif) is usually a constant and doesn't usually have side effects, this can be evaluated some more at compile time:
(%apply ??? a 'b '(c d e)) ; where ??? is an implementation of aif's body
Even if aif isn't a constant, as long as the compiler knows enough about what aif will be (its type), it might be able to reduce (%compiler-of aif) anyway.
Now is when (%apply ??? a 'b '(c d e)) would be inlined if possible, in the hopes of compiling '(c d e). With all of Eight's 'leak, 'comma, and 'asterix, I think that might take a few more techniques than I've thought about. My language's approach to afn would probably work a bit more like this:
(%apply (%compiler-of aif) '(a b c d e))
(%apply ??? (list (fn () a)
(fn (it) b)
(fn () c)
(fn (it) d)
(fn () e)))
...and therefore avoid having to working with syntax in the method body. Then again, this language is probably going to be considerably more mind-melting to try to read. Here's a generous mockup of the kind of thing I have in mind for the base language (which I'm calling Blade):
