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add note about "quotable" to docs for make-constructor-style-printer

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Ryan Culpepper 2020-09-03 16:54:22 +02:00
parent b9e4b5dbb1
commit 9464bc3274
1 changed files with 21 additions and 0 deletions
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pkgs/racket-doc/scribblings/reference/struct.scrbl
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@ -661,6 +661,27 @@ The function also cooperates with @racket[pretty-print]:
(pretty-write (point #e3e6 #e4e6)))
]
Note that the printer uses a separate property,
@racket[prop:custom-print-quotable], to determine whether a struct
instance is quotable. If so, the printer may print it in
@racket[write] mode it in certain contexts, such as within a list. For
example:
@examples[#:eval struct-eval #:label #f
(print (list (point 1 2) (point 3 4)))
]
Use @racket[#:property prop:custom-print-quotable 'never] to prevent a
struct instance from being considered quotable. For example:
@examples[#:eval struct-eval #:label #f
(struct point2 (x y)
#:property prop:custom-print-quotable 'never
#:methods gen:custom-write
[(define write-proc
(make-constructor-style-printer
(lambda (obj) 'point)
(lambda (obj) (list (point2-x obj) (point2-y obj)))))])
(print (list (point2 1 2) (point2 3 4)))
]
Keyword arguments can be simulated with @racket[unquoted-printing-string]:
@examples[#:eval struct-eval #:label #f