46 lines
1.5 KiB
Racket
46 lines
1.5 KiB
Racket
#reader(lib "docreader.ss" "scribble")
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@require[(lib "manual.ss" "scribble")]
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@require[(lib "eval.ss" "scribble")]
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@require["guide-utils.ss"]
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@title[#:tag "guide:keywords"]{Keywords}
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A @defterm{keyword} value is similar to a symbol (see
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@secref["guide:symbols"]), but its printed form is prefixed with
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@litchar{#:}.
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@refdetails/gory["mz:parse-keyword"]{the syntax of keywords}
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@examples[
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(string->keyword "apple")
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'#:apple
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(eq? '#:apple (string->keyword "apple"))
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]
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More precisely, a keyword is analogous to an identifier; in the same
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way that an identifier can be quoted to produce a symbol, a keyword
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can be quoted to produce a value. The same term ``keyword'' is used in
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both cases, but we sometimes use @defterm{keyword value} to refer more
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specifically to the result of a quote-keyword expression or of
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@scheme[string->keyword]. An unquoted keyword is not an expression,
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just as an unquoted identifier does not produce a symbol:
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@examples[
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not-a-symbol-expression
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#:not-a-keyword-expression
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]
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Despite their similarities, keywords are used in a different way than
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identifiers or symbols. Keywords are intented for use (unquoted) as
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special markers in argument lists and in certain syntactic forms.
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@italic{Need some examples here, once we have more keyword-based
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procedures and syntax in place...}
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Keywords should not be used simply as another kind of symbol. Use
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symbols, instead of keywords, for run-time flags and enumerations.
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@examples[
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(code:line (bytes->path #"/usr/tmp" 'unix) (code:comment #, @t{@scheme['unix], not @scheme['#:unix]}))
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]
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