suzanne.soy/fear-of-macros
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This commit is contained in:
Greg Hendershott 2012-11-02 08:35:40 -04:00
parent bf7c9f0ace
commit 1c10e60943
1 changed files with 9 additions and 11 deletions
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main.rkt
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@ -768,7 +768,8 @@ that using an additional, nested @racket[syntax-case]:
(syntax-case stx ()
[(_ a b (args ...) body0 body ...)
(syntax-case (datum->syntax stx
(string->symbol (format "~a-~a" #'a #'b))) ()
(string->symbol (format "~a-~a" #'a #'b)))
()
[name #'(define (name args ...)
body0 body ...)])]))
]
@ -794,23 +795,19 @@ Let's try to use our new version:
Hmm. @racket[foo-bar] is @italic{still} not defined. Back to the Macro
Stepper. It says now we're expanding to:
@racketblock[
(define (|#<syntax:11:24foo>-#<syntax:11:28 bar>|) #t)
]
@racketblock[(define (|#<syntax:11:24foo>-#<syntax:11:28 bar>|) #t)]
Oh right: @racket[#'a] and @racket[#'b] are syntax objects. Therefore
@racketblock[(string->symbol (format "~a-~a" #'a #'b))]
is something like
is the printed form of both syntax objects, joined by a hyphen:
@racketblock[|#<syntax:11:24foo>-#<syntax:11:28 bar>|]
---the printed form of both syntax objects, joined by a hyphen.
Instead we want the datum in the syntax objects (such as the symbols
@racket[foo] and @racket[bar]). Let's use @racket[syntax->datum] to
get it:
Instead we want the datum in the syntax objects, such as the symbols
@racket[foo] and @racket[bar]. Which we get using
@racket[syntax->datum]:
@i[
(define-syntax (hyphen-define/ok1 stx)
@ -819,7 +816,8 @@ get it:
(syntax-case (datum->syntax stx
(string->symbol (format "~a-~a"
(syntax->datum #'a)
(syntax->datum #'b)))) ()
(syntax->datum #'b))))
()
[name #'(define (name args ...)
body0 body ...)])]))
(hyphen-define/ok1 foo bar () #t)