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example of unquoted-printing-string in make-constructor-style-printer

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Ryan Culpepper 2017-08-04 11:09:45 -04:00
parent 4a71936f23
commit 5519a8ab45
1 changed files with 23 additions and 1 deletions
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pkgs/racket-doc/scribblings/reference/struct.scrbl
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@ -640,13 +640,35 @@ See @racket[make-prefab-struct] for a description of valid key shapes.}
The function also cooperates with @racket[pretty-print]:
@examples[#:eval struct-eval
@examples[#:eval struct-eval #:label #f
(parameterize ((pretty-print-columns 10))
(pretty-print (point #e3e6 #e4e6)))
(parameterize ((pretty-print-columns 10))
(pretty-write (point #e3e6 #e4e6)))
]
Keyword arguments can be simulated with @racket[unquoted-printing-string]:
@examples[#:eval struct-eval #:label #f
(code:comment "Private implementation")
(struct kwpoint-impl (x y)
#:methods gen:custom-write
[(define write-proc
(make-constructor-style-printer
(lambda (obj) 'kwpoint)
(lambda (obj)
(list (unquoted-printing-string "#:x")
(kwpoint-impl-x obj)
(unquoted-printing-string "#:y")
(kwpoint-impl-y obj)))))])
(code:comment "Public ``constructor''")
(define (kwpoint #:x x #:y y)
(kwpoint-impl x y))
(code:comment "Example use")
(print (kwpoint #:x 1 #:y 2))
(write (kwpoint #:x 3 #:y 4))
]
@history[#:added "6.3"]{}
}