78 lines
2.4 KiB
HTML
78 lines
2.4 KiB
HTML
<html>
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<head>
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<!-- This file has been generated by unroff 1.0, 03/21/96 19:29:47. -->
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<link rev="made" href="mailto:net@informatik.uni-bremen.de">
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<title>unroff Programmer's Manual, section 12.</title>
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</head><body>
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<h2><a name="section12">12.</a> <tt> </tt>Tables
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt><i>unroff
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</i>provides simple hash tables as a new first class data type
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<i>table</i>.<tt> </tt>
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Each table entry associates an arbitrary Scheme object with
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a key (a Scheme string or symbol).<tt> </tt>
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Tables are useful for various purposes; for example, the Scheme code
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delivered with
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<i>unroff
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</i>maintains hash tables to store information about number registers,
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options, fonts, and for other bookkeeping tasks.<tt> </tt>
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<h2>
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(table? <i>obj</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>The type predicate for the new type; it returns #t if
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<i>obj
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</i>is a member of the type
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<i>table</i>,
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otherwise #f.<tt> </tt>
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<h2>
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(make-table <i>size</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Returns a new table of the specified size.<tt> </tt>
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<i>size
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</i>is a positive integer.<tt> </tt>
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The smaller the size, the more collisions occur as entries
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are added to the table.<tt> </tt>
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However, the hash function employed by the table primitives
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ensures that no collisions occur in tables of size
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256^<i>n
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</i>if all keys have a length less than or equal to
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<i>n</i>.<tt> </tt>
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<h2>
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(table-store! <i>table</i> <i>key</i> <i>obj</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive stores the Scheme object
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<i>obj
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</i>under the given
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<i>key
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</i>in the given
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<i>table</i>.<tt> </tt>
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The key argument must be a string or a symbol.<tt> </tt>
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<h2>
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(table-lookup <i>table</i> <i>key</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>This primitive checks whether an object is stored in the given
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<i>table
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</i>under the specified
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<i>key</i>,
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and if so, returns the object.<tt> </tt>
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If no object is stored under
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<i>key</i>,
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<i>table-lookup
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</i>returns #f.<tt> </tt>
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<h2>
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(table-remove! <i>table</i> <i>key</i>)
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</h2>
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<p>
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 <tt> </tt> <tt> </tt> <tt> </tt>Removes the entry selected by
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<i>key
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</i>from the specified table.<tt> </tt>
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<p><hr>
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Markup created by <em>unroff</em> 1.0, <tt> </tt> <tt> </tt>March 21, 1996, <tt> </tt> <tt> </tt>net@informatik.uni-bremen.de</body>
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</html>
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