What is the reason for using syntax-rules instead of syntax-parse? (To maintain RnRs compatibility?)
RAC On Aug 9, 2011, at 8:15 AM, Neil Van Dyke <n...@neilvandyke.org> wrote: > BTW, for future readers... in this example: > > (define-syntax if* > (syntax-rules (then else) > ((_ ?test (then ?consequent) (else ?alternate)) > (if ?test ?consequent ?alternate)))) > > The "?" part of the pattern variables is just a naming convention of > individual programmers. The "?" is the first character of the pattern > variable identifier, not special syntax. > > I've tried various naming conventions here, including "?". Once my macro > clauses got large, with a mix of a number of pattern variables as well as > Racket identifiers to be captured, I settled on making the pattern variable > identifiers all-upppercase: > > (define-syntax if* > (syntax-rules (then else) > ((_ TEST (then CONSEQUENT) (else ALTERNATE)) > (if TEST CONSEQUENT ALTERNATE)))) > > This example is too small too appreciate the difference, with "if" being the > only Racket identifier. Imagine you had a "syntax-rules" clause with block > of code with 20 Racket identifiers in it, and 3 pattern variables. You'd > want the pattern variables scattered throughout this to really stand out. At > least on my screen, all-caps does that better than "?", and all-caps also > takes up less horizontal space, which can get to be an issue with patterns > that you're trying to keep to a single line for readability symmetries. > Anyone else looking at the code will instantly see which convention you're > using, so you can use whatever you want. > > I have a few more useful conventions for "syntax-rules", from which people > can pick&choose depending on the situation and preferences, but no time today > to type them. Typing them up might have to wait for pounding out a chapter > of my tentative practical Racket book. (Not trying to sell anything; book > will be free in Scribble format, probably as a PLaneT package that installs > the book into your searchable local copies of Racket documentation.) > > -- > http://www.neilvandyke.org/ > > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
