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beautiful-racket/br/datum.rkt

35 lines
1.4 KiB
Racket

#lang racket/base
(require (for-syntax racket/base br/syntax) br/define)
(provide (all-defined-out))
;; read "foo bar" the same way as "(foo bar)"
;; other "bar" is dropped, which is too astonishing
(define (string->datum str)
(let ([result (read (open-input-string (format "(~a)" str)))])
(if (= (length result) 1)
(car result)
result)))
(define-syntax format-datum
(λ(stx)
(syntax-case stx (quote datum)
[(_ (quote <datum-template>) <arg> ...)
#'(format-datum (datum <datum-template>) <arg> ...)]
[(_ (datum datum-template) <arg> ...)
(syntax-let ([#'format-string (format "~a" (syntax->datum #'datum-template))])
#'(string->datum (apply format format-string (map (λ(arg) (if (syntax? arg)
(syntax->datum arg)
arg)) (list <arg> ...)))))])))
(module+ test
(require rackunit)
(check-equal? (string->datum "foo") 'foo)
(check-equal? (string->datum "(foo bar)") '(foo bar))
(check-equal? (string->datum "foo bar") '(foo bar))
(check-equal? (string->datum "42") 42)
(check-equal? (format-datum '(~a-bar-~a) "foo" "zam") '(foo-bar-zam))
(check-equal? (format-datum (datum (~a-bar-~a)) "foo" "zam") '(foo-bar-zam))
(check-equal? (format-datum '~a "foo") 'foo)
(check-equal? (format-datum (datum ~a) "foo") 'foo))