[racket] Many datums in syntax-parse

2013/1/22 Danny Yoo <dyoo at hashcollision.org>:
>> Is there an equivalent to #:datums (old-timestamp time-of-day …)
>> in syntax-parse?

A nice puzzle. Now Ryan added #literal-datums that's of course
the way to go, but here is a solution.

First define a syntax class that matches a literal datum.
    (define-syntax-class <drawing> (pattern (~datum drawing)))

Then make the convention that  drawing  has the syntax class <drawing>.
    (define-conventions drawing-datum
      [#rx"^drawing$" <drawing>]

Finally use
    (syntax-parse stx
       #:conventions (drawing-datum)
     ...)

The complete examples is as follows:

#lang racket/base

(require ragg/examples/simple-line-drawing/lexer
         ragg/examples/simple-line-drawing/grammar
         syntax/parse
         (for-syntax syntax/parse)
         (for-syntax racket/base))

(define-syntax (define-datums stx)
  (syntax-parse stx
    [(_ name ...)
     #'(begin
         (define-syntax-class name (pattern (~datum name)))
         ...)]))

(define-datums drawing row repeat chunk)

(define-conventions simple-line-datums
  [#rx"^drawing$" drawing]
  [#rx"^row$"     row]
  [#rx"^repeat$"  repeat]
  [#rx"^hunk$"    chunk])


(define an-stx
  (parse (tokenize (open-input-string "3 9 X;
6 3 b 3 X 3 b;
3 9 X;"))))

(syntax-parse an-stx
  #:conventions (simple-line-datums)
  [(drawing r ...)
   (printf "I see: ~s\n" #'(r ...))])

-- 
Jens Axel Søgaard