59 lines
1.9 KiB
Racket
59 lines
1.9 KiB
Racket
#lang scribble/doc
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@require[scribble/manual]
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@require[scribble/eval]
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@require["guide-utils.ss"]
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@title[#:tag "vectors"]{Vectors}
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A @defterm{vector} is a fixed-length array of arbitrary
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values. Unlike a list, a vector supports constant-time access and
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update of its elements.
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A vector prints similar to a list---as a parenthesized sequence of its
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elements---but a vector is prefixed with @litchar{#}. For a vector as
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an expression, an optional length can be supplied. Also, a vector as
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an expression implicitly quotes the forms for its content, which means
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that identifiers and parenthesized forms in a vector constant
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represent symbols and lists.
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@refdetails/gory["parse-vector"]{the syntax of vectors}
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@examples[
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(eval:alts #, @schemevalfont{#("a" "b" "c")} #("a" "b" "c"))
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(eval:alts #, @schemevalfont{#(name (that tune))} #(name (that tune)))
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(vector-ref #("a" "b" "c") 1)
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(vector-ref #(name (that tune)) 1)
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]
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When the last @math{n} vector elements of a vector are the same value
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(as determined by @scheme[eq?]), then the last @math{n-1} instances
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are omitted from the printed form. The vector length shown after the
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leading @litchar{#} effectively indicates when repeated trailing
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elements are omitted. The same conventions apply for vectors as
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expressions.
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@examples[
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(define v (make-vector 100 "."))
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v
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(vector-set! v 1 "!")
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v
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(vector-ref #10("." "?") 8)
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]
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Like strings, a vector is either mutable or immutable, and vectors
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written directly as expressions are immutable.
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Vector can be converted to lists and vice-versa via
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@scheme[list->vector] and @scheme[vector->list]; such conversions are
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particularly useful in combination with predefined procedures on
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lists. When allocating extra lists seems too expensive, use consider
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using looping forms like @scheme[fold-for], which recognize vectors as
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well as lists.
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@examples[
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(list->vector (map string-titlecase
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(vector->list #("three" "blind" "mice"))))
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]
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@refdetails["vectors"]{vectors and vector procedures}
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