9835bc2f7b
* fix cond intro 'text-expr' typo in guide * fix quote in quote title * for -> form in quasiquote unquote-splicing shorthand
66 lines
2.3 KiB
Racket
66 lines
2.3 KiB
Racket
#lang scribble/doc
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@(require scribble/manual scribble/eval "guide-utils.rkt")
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@title[#:tag "quote"]{Quoting: @racket[quote] and @racketvalfont{@literal{'}}}
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@refalso["quote"]{@racket[quote]}
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The @racket[quote] form produces a constant:
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@specform[(#,(racketkeywordfont "quote") datum)]
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The syntax of a @racket[datum] is technically specified as anything
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that the @racket[read] function parses as a single element. The value
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of the @racket[quote] form is the same value that @racket[read] would
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produce given @racket[_datum].
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The @racket[_datum] can be a symbol, a boolean, a number, a (character
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or byte) string, a character, a keyword, an empty list, a pair (or
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list) containing more such values, a vector containing more such
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values, a hash table containing more such values, or a box containing
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another such value.
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@examples[
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(eval:alts (#,(racketkeywordfont "quote") apple) 'apple)
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(eval:alts (#,(racketkeywordfont "quote") #t) #t)
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(eval:alts (#,(racketkeywordfont "quote") 42) 42)
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(eval:alts (#,(racketkeywordfont "quote") "hello") "hello")
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(eval:alts (#,(racketkeywordfont "quote") ()) '())
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(eval:alts (#,(racketkeywordfont "quote") ((1 2 3) #2("z" x) . the-end)) '((1 2 3) #2("z" x) . the-end))
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(eval:alts (#,(racketkeywordfont "quote") (1 2 #,(racketparenfont ".") (3))) '(1 2 . (3)))
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]
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As the last example above shows, the @racket[_datum] does not have to
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match the normalized printed form of a value. A @racket[_datum] cannot
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be a printed representation that starts with @litchar{#<}, so it
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cannot be @|void-const|, @|undefined-const|, or a procedure.
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The @racket[quote] form is rarely used for a @racket[_datum] that is a
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boolean, number, or string by itself, since the printed forms of those
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values can already be used as constants. The @racket[quote] form is
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more typically used for symbols and lists, which have other meanings
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(identifiers, function calls, etc.) when not quoted.
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An expression
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@specform[(quote @#,racketvarfont{datum})]
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is a shorthand for
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@racketblock[
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(#,(racketkeywordfont "quote") #,(racket _datum))
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]
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and this shorthand is almost always used instead of
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@racket[quote]. The shorthand applies even within the @racket[_datum],
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so it can produce a list containing @racket[quote].
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@refdetails["parse-quote"]{the @racketvalfont{'} shorthand}
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@examples[
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'apple
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'"hello"
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'(1 2 3)
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(display '(you can 'me))
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]
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