4 ms·

I'm not sure how your cond example is related to vector syntax. The decision to use (partition 2 ...) style pairs, rather than extra brackets is orthogonal. Th

I'm not sure how your cond example is related to vector syntax. The decision to use (partition 2 ...) style pairs, rather than extra brackets is orthogonal. The more important point of literal syntax for composites other than lists is the fact that they are resolved at read time. This means you don't need a macro to have grouping. With (some-macro ((f x) (g y))), you need to force expansion inside the parens. Quoting (some-function '((f x) (g x))) requires forcing evaluation in your function. You could use (vector (f x) (g x)), but now that means some-function gets a vector argument and some-macro would get a list argument with first element 'vector. In Clojure, (some-function-or-macro [(f x) (g y)]) both have a vector as an argument because of the read-time behavior of data structure literals. Huge win in my book.

kenko 13y ago
The cond example isn't related to vector-style syntax. There are two options: either the unpaired elements are the last (so you can get them from rest parameters) or the unpaired elements are already grouped somehow (for instance, by being in a vector). Cond does the former, let does the latter. I'm not sure why you're mentioning vector syntax at all since the comment you're replying to was specifically talking only about grouping. Literal syntax for composites other than lists is totally unrelated to this. I actually really don't understand why if you had (some-macro ((f x) (g y))) you'd have to "force expansion inside the parens", since well-behaved macros won't expand their arguments. You'd iterate through the elements in the parens, but ... that's what you'd do with clojure-style partition macros, too, you'd just call partition first. For a function call the obvious choice, and one you see in Scheme/Racket quite frequently, is either `(,(f x) ,(g y)) for your second example, or even (list (f x) (g y)). Yeah, then your macro gets a list whose first element is 'list, but ... so what? Your macro probably shouldn't be looking inside what it receives anyway, and if it does then it should be documented that it expects a literal ((foo bar) (baz quux)) or whatever (just as in Clojure you can't write (let (vector 'a 'b) (+ a b)) and have that work).

kenko 13y ago

The cond example isn't related to vector-style syntax. There are two options: either the unpaired elements are the last (so you can get them from rest parameters) or the unpaired elements are already grouped somehow (for instance, by being in a vector). Cond does the former, let does the latter. I'm not sure why you're mentioning vector syntax at all since the comment you're replying to was specifically talking only about grouping. Literal syntax for composites other than lists is totally unrelated to this. I actually really don't understand why if you had (some-macro ((f x) (g y))) you'd have to "force expansion inside the parens", since well-behaved macros won't expand their arguments. You'd iterate through the elements in the parens, but ... that's what you'd do with clojure-style partition macros, too, you'd just call partition first. For a function call the obvious choice, and one you see in Scheme/Racket quite frequently, is either `(,(f x) ,(g y)) for your second example, or even (list (f x) (g y)). Yeah, then your macro gets a list whose first element is 'list, but ... so what? Your macro probably shouldn't be looking inside what it receives anyway, and if it does then it should be documented that it expects a literal ((foo bar) (baz quux)) or whatever (just as in Clojure you can't write (let (vector 'a 'b) (+ a b)) and have that work).