4288c6c2c7
punctuations outside of the form, as it does with quote punctuations.
So things like this
#, @foo{...}
that required the space to make the @foo read as a scribble form are
now better written as
@#,foo{...}
This changes all such occurrences. (In case you see this change in
your files and are worried that there might be changes: I mechanically
verified that the result of `read'ing the modified files is identical
to the previous version.)
svn: r15111
70 lines
2.4 KiB
Racket
70 lines
2.4 KiB
Racket
#lang scribble/doc
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@(require scribble/manual
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scribble/eval
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"guide-utils.ss")
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@title[#:tag "quote"]{Quoting: @scheme[quote] and @schemevalfont{'}}
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@refalso["quote"]{@scheme[quote]}
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The @scheme[quote] form produces a constant:
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@specform[(#,(schemekeywordfont "quote") datum)]
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The syntax of a @scheme[datum] is technically specified as anything
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that the @scheme[read] function parses as a single element. The value
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of the @scheme[quote] form is the same value that @scheme[read] would
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produce given @scheme[_datum].
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To a good approximation, the resulting value is such that
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@scheme[_datum] is the value's printed representation. Thus, it can be
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a symbol, a boolean, a number, a (character or byte) string, a
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character, a keyword, an empty list, a pair (or list) containing more
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such values, a vector containing more such values, a hash table
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containing more such values, or a box containing another such value.
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@examples[
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(eval:alts (#,(schemekeywordfont "quote") apple) 'apple)
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(eval:alts (#,(schemekeywordfont "quote") #t) #t)
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(eval:alts (#,(schemekeywordfont "quote") 42) 42)
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(eval:alts (#,(schemekeywordfont "quote") "hello") "hello")
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(eval:alts (#,(schemekeywordfont "quote") ()) '())
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(eval:alts (#,(schemekeywordfont "quote") ((1 2 3) #2("z" x) . the-end)) '((1 2 3) #2("z" x) . the-end))
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(eval:alts (#,(schemekeywordfont "quote") (1 2 #,(schemeparenfont ".") (3))) '(1 2 . (3)))
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]
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As the last example above shows, the @scheme[_datum] does not have to
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be the normalized printed form of a value. A
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@scheme[_datum] cannot be a printed representation that starts with
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@litchar{#<}, however, so it cannot be @|void-const|,
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@|undefined-const|, or a procedure.
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The @scheme[quote] form is rarely used for a @scheme[_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 @scheme[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 @#,schemevarfont{datum})]
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is a shorthand for
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@schemeblock[
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(#,(schemekeywordfont "quote") #,(scheme _datum))
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]
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and this shorthand is almost always used instead of
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@scheme[quote]. The shorthand applies even within the @scheme[_datum],
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so it can produce a list containing @scheme[quote].
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@refdetails["parse-quote"]{the @schemevalfont{'} 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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