Say you want a three-state machine where the states are labeled 'go, 'stop, 'warning and you use a stream of signals to switch between states say 'button-down 'x 'y, you can eliminate the quotes from the surface syntax with macros that place the quotes on the right pieces. Instead of symbols you can think string and/or nests of these.
On Nov 25, 2013, at 9:23 AM, Ben Duan <yfe...@gmail.com> wrote: > > - changing evaluation order, > > - implementing a data sublanguage, and > > - creating new binding forms. > > Thanks for the insights. But what does "data sublanguage" mean? > > > On Sat, Nov 23, 2013 at 2:46 PM, John Clements <cleme...@brinckerhoff.org> > wrote: > I'm preparing a 10-minute lightning talk on hygienic macros in rust (preview: > I'm barely going to *mention* hygiene), and in the process, I've been > surveying some of the Rust macros, and roughly categorizing them in terms of > the "three canonical categories" that Matthias described--apologies if I'm > misrepresenting him/you: > - changing evaluation order, > - implementing a data sublanguage, and > - creating new binding forms. > > Some of the Rust macros seem to fall into a fourth category, which arises > from the fact that certain things are not expressions: > > - abstracting over things that are not expressions. > > For instance: > > cmp_impl!(impl Eq, eq, ne) > cmp_impl!(impl TotalEq, equals) > cmp_impl!(impl Ord, lt, gt, le, ge) > cmp_impl!(impl TotalOrd, cmp -> cmp::Ordering) > > Each of these expands into a top-level "impl" declaration, extending > implementations of, e.g., Ord, from type T to type Ratio<T>. > > More generally, it seems to me that every time you constrain first-class-ness > by making things not-first-class (e.g. module-level stuff in Racket), you > will be required to use macros to abstract over these things. > > Thoughts? > > Back to writing my talk... > > John > > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users > > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
