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<title>rnrs hashtables (Guile Reference Manual)</title>
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Next: <a href="rnrs-enums.html" accesskey="n" rel="next">rnrs enums</a>, Previous: <a href="rnrs-syntax_002dcase.html" accesskey="p" rel="prev">rnrs syntax-case</a>, Up: <a href="R6RS-Standard-Libraries.html" accesskey="u" rel="up">R6RS Standard Libraries</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
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<h4 class="subsubsection" id="rnrs-hashtables-1"><span>7.6.2.25 rnrs hashtables<a class="copiable-link" href="#rnrs-hashtables-1"> ¶</a></span></h4>
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<p>The <code class="code">(rnrs hashtables (6))</code> library provides structures and
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procedures for creating and accessing hash tables. The hash tables API
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defined by R6RS is substantially similar to both Guile’s native hash
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tables implementation as well as the one provided by SRFI-69;
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See <a class="xref" href="Hash-Tables.html">Hash Tables</a>, and <a class="ref" href="SRFI_002d69.html">SRFI-69 - Basic hash tables</a>, respectively. Note that you can
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write portable R6RS library code that manipulates SRFI-69 hash tables
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(by importing the <code class="code">(srfi :69)</code> library); however, hash tables
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created by one API cannot be used by another.
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</p>
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<p>Like SRFI-69 hash tables—and unlike Guile’s native ones—R6RS hash
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tables associate hash and equality functions with a hash table at the
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time of its creation. Additionally, R6RS allows for the creation
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(via <code class="code">hashtable-copy</code>; see below) of immutable hash tables.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002deq_002dhashtable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-eq-hashtable</strong><a class="copiable-link" href="#index-make_002deq_002dhashtable"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-make_002deq_002dhashtable-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-eq-hashtable</strong> <var class="def-var-arguments">k</var><a class="copiable-link" href="#index-make_002deq_002dhashtable-1"> ¶</a></span></dt>
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<dd><p>Returns a new hash table that uses <code class="code">eq?</code> to compare keys and
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Guile’s <code class="code">hashq</code> procedure as a hash function. If <var class="var">k</var> is given,
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it specifies the initial capacity of the hash table.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002deqv_002dhashtable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-eqv-hashtable</strong><a class="copiable-link" href="#index-make_002deqv_002dhashtable"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-make_002deqv_002dhashtable-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-eqv-hashtable</strong> <var class="def-var-arguments">k</var><a class="copiable-link" href="#index-make_002deqv_002dhashtable-1"> ¶</a></span></dt>
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<dd><p>Returns a new hash table that uses <code class="code">eqv?</code> to compare keys and
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Guile’s <code class="code">hashv</code> procedure as a hash function. If <var class="var">k</var> is given,
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it specifies the initial capacity of the hash table.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002dhashtable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-hashtable</strong> <var class="def-var-arguments">hash-function equiv</var><a class="copiable-link" href="#index-make_002dhashtable"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-make_002dhashtable-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-hashtable</strong> <var class="def-var-arguments">hash-function equiv k</var><a class="copiable-link" href="#index-make_002dhashtable-1"> ¶</a></span></dt>
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<dd><p>Returns a new hash table that uses <var class="var">equiv</var> to compare keys and
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<var class="var">hash-function</var> as a hash function. <var class="var">equiv</var> must be a procedure
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that accepts two arguments and returns a true value if they are
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equivalent, <code class="code">#f</code> otherwise; <var class="var">hash-function</var> must be a procedure
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that accepts one argument and returns a non-negative integer.
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</p>
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<p>If <var class="var">k</var> is given, it specifies the initial capacity of the hash
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table.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-hashtable_003f"> ¶</a></span></dt>
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<dd><p>Returns <code class="code">#t</code> if <var class="var">obj</var> is an R6RS hash table, <code class="code">#f</code>
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otherwise.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dsize"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-size</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dsize"> ¶</a></span></dt>
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<dd><p>Returns the number of keys currently in the hash table <var class="var">hashtable</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dref"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-ref</strong> <var class="def-var-arguments">hashtable key default</var><a class="copiable-link" href="#index-hashtable_002dref"> ¶</a></span></dt>
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<dd><p>Returns the value associated with <var class="var">key</var> in the hash table
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<var class="var">hashtable</var>, or <var class="var">default</var> if none is found.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dset_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-set!</strong> <var class="def-var-arguments">hashtable key obj</var><a class="copiable-link" href="#index-hashtable_002dset_0021"> ¶</a></span></dt>
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<dd><p>Associates the key <var class="var">key</var> with the value <var class="var">obj</var> in the hash table
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<var class="var">hashtable</var>, and returns an unspecified value. An <code class="code">&assertion</code>
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condition is raised if <var class="var">hashtable</var> is immutable.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002ddelete_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-delete!</strong> <var class="def-var-arguments">hashtable key</var><a class="copiable-link" href="#index-hashtable_002ddelete_0021"> ¶</a></span></dt>
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<dd><p>Removes any association found for the key <var class="var">key</var> in the hash table
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<var class="var">hashtable</var>, and returns an unspecified value. An <code class="code">&assertion</code>
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condition is raised if <var class="var">hashtable</var> is immutable.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dcontains_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-contains?</strong> <var class="def-var-arguments">hashtable key</var><a class="copiable-link" href="#index-hashtable_002dcontains_003f"> ¶</a></span></dt>
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<dd><p>Returns <code class="code">#t</code> if the hash table <var class="var">hashtable</var> contains an
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association for the key <var class="var">key</var>, <code class="code">#f</code> otherwise.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dupdate_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-update!</strong> <var class="def-var-arguments">hashtable key proc default</var><a class="copiable-link" href="#index-hashtable_002dupdate_0021"> ¶</a></span></dt>
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<dd><p>Associates with <var class="var">key</var> in the hash table <var class="var">hashtable</var> the result
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of calling <var class="var">proc</var>, which must be a procedure that takes one
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argument, on the value currently associated <var class="var">key</var> in
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<var class="var">hashtable</var>—or on <var class="var">default</var> if no such association exists.
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An <code class="code">&assertion</code> condition is raised if <var class="var">hashtable</var> is
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immutable.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dcopy"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-copy</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dcopy"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-hashtable_002dcopy-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-copy</strong> <var class="def-var-arguments">hashtable mutable</var><a class="copiable-link" href="#index-hashtable_002dcopy-1"> ¶</a></span></dt>
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<dd><p>Returns a copy of the hash table <var class="var">hashtable</var>. If the optional
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argument <var class="var">mutable</var> is provided and is a true value, the new hash
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table will be mutable.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dclear_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-clear!</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dclear_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-hashtable_002dclear_0021-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-clear!</strong> <var class="def-var-arguments">hashtable k</var><a class="copiable-link" href="#index-hashtable_002dclear_0021-1"> ¶</a></span></dt>
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<dd><p>Removes all of the associations from the hash table <var class="var">hashtable</var>.
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The optional argument <var class="var">k</var>, which specifies a new capacity for the
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hash table, is accepted by Guile’s <code class="code">(rnrs hashtables)</code>
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implementation, but is ignored.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dkeys"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-keys</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dkeys"> ¶</a></span></dt>
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<dd><p>Returns a vector of the keys with associations in the hash table
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<var class="var">hashtable</var>, in an unspecified order.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dentries"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-entries</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dentries"> ¶</a></span></dt>
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<dd><p>Return two values—a vector of the keys with associations in the hash
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table <var class="var">hashtable</var>, and a vector of the values to which these keys
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are mapped, in corresponding but unspecified order.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dequivalence_002dfunction"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-equivalence-function</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dequivalence_002dfunction"> ¶</a></span></dt>
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<dd><p>Returns the equivalence predicated use by <var class="var">hashtable</var>. This
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procedure returns <code class="code">eq?</code> and <code class="code">eqv?</code>, respectively, for hash
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tables created by <code class="code">make-eq-hashtable</code> and
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<code class="code">make-eqv-hashtable</code>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dhash_002dfunction"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-hash-function</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dhash_002dfunction"> ¶</a></span></dt>
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<dd><p>Returns the hash function used by <var class="var">hashtable</var>. For hash tables
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created by <code class="code">make-eq-hashtable</code> or <code class="code">make-eqv-hashtable</code>,
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<code class="code">#f</code> is returned.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-hashtable_002dmutable_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">hashtable-mutable?</strong> <var class="def-var-arguments">hashtable</var><a class="copiable-link" href="#index-hashtable_002dmutable_003f"> ¶</a></span></dt>
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<dd><p>Returns <code class="code">#t</code> if <var class="var">hashtable</var> is mutable, <code class="code">#f</code> otherwise.
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</p></dd></dl>
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<p>A number of hash functions are provided for convenience:
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-equal_002dhash"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">equal-hash</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-equal_002dhash"> ¶</a></span></dt>
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<dd><p>Returns an integer hash value for <var class="var">obj</var>, based on its structure and
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current contents. This hash function is suitable for use with
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<code class="code">equal?</code> as an equivalence function.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dhash-2"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-hash</strong> <var class="def-var-arguments">string</var><a class="copiable-link" href="#index-string_002dhash-2"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-symbol_002dhash-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">symbol-hash</strong> <var class="def-var-arguments">symbol</var><a class="copiable-link" href="#index-symbol_002dhash-1"> ¶</a></span></dt>
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<dd><p>These procedures are identical to the ones provided by Guile’s core
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library. See <a class="xref" href="Hash-Table-Reference.html">Hash Table Reference</a>, for documentation.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dci_002dhash-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-ci-hash</strong> <var class="def-var-arguments">string</var><a class="copiable-link" href="#index-string_002dci_002dhash-1"> ¶</a></span></dt>
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<dd><p>Returns an integer hash value for <var class="var">string</var> based on its contents,
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ignoring case. This hash function is suitable for use with
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<code class="code">string-ci=?</code> as an equivalence function.
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</p></dd></dl>
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