ac26fe7554
Also, updates some of the mzlib files to point at `racket/*' libraries rather than to `scheme/*' ones.
36 lines
1.4 KiB
Racket
36 lines
1.4 KiB
Racket
#lang scribble/doc
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@(require "mz.rkt")
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@title[#:tag "portstructs"]{Structures as Ports}
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@defthing[prop:input-port struct-type-property?]
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@defthing[prop:output-port struct-type-property?]
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The @racket[prop:input-port] and @racket[prop:output-port] structure type
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properties identify structure types whose instances can serve as input
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and output ports, respectively.
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Each property value can be either of the following:
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@itemize[
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@item{An input port (for @racket[prop:input-port]) or output port
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(for @racket[prop:output-port]): In this case, using the structure
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as port is equivalent to using the given input or output port.}
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@item{An exact, non-negative integer between @racket[0] (inclusive) and
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the number of non-automatic fields in the structure type (exclusive, not
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counting supertype fields): The integer identifies a field in
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the structure, and the field must be designated as immutable. If the
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field contains an input port (for @racket[prop:input-port]) or
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output port (for @racket[prop:output-port]), the port is used.
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Otherwise, an empty string input port is used for @racket[prop:input-port],
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and a port that discards all data is used for @racket[prop:output-port].}
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]
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Some procedures, such as @racket[file-position], work on both input
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and output ports. When given an instance of a structure type with both
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the @racket[prop:input-port] and @racket[prop:output-port] properties,
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the instance is used as an input port.
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