klisp

an open source interpreter for the Kernel Programming Language.
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     36 <h2 class="chapter">13 Keyed Variables</h2>
     37 
     38 <p><a name="index-keyed-variables-161"></a>
     39   A keyed variable is a device that associates a non-symbolic key (in
     40 the form of an accessor applicative) with a value depending on the
     41 context in which lookup occurs.  Kernel provides two types of keyed
     42 variables: dynamic &amp; static.  Keyed Dynamic Variables use the dynamic
     43 extent as context and Keyed Static Variables use the dynamic
     44 environment.
     45 
     46 <h3 class="section">13.1 Keyed Dynamic Variables</h3>
     47 
     48 <p><a name="index-keyed-dynamic-variables-162"></a><!-- add cf xref static -->
     49 <!-- TODO add xref to dynamic extent -->
     50   A keyed dynamic variable is a device that associates a non-symbolic
     51 key (in the form of an accessor applicative) with a value depending on
     52 the dynamic extent in which lookup occurs.
     53 
     54 <div class="defun">
     55 &mdash; Applicative: <b>make-keyed-dynamic-variable</b> (<var>make-keyed-dynamic-variable</var>)<var><a name="index-make_002dkeyed_002ddynamic_002dvariable-163"></a></var><br>
     56 <blockquote><p>  Returns a list of the form <code>(b a)</code>, where <code>b</code> and <code>a</code>
     57 are applicatives, as follows.  Each call to
     58 <code>make-keyed-dynamic-variable</code> returns different <code>b</code> and
     59 <code>a</code>.
     60 
     61           <ul>
     62 <li><code>b</code> is an applicative that takes two arguments, the second of
     63 which must be a combiner.  It calls its second argument with no
     64 operands (nil operand tree) in a fresh empty environment, and returns
     65 the result.
     66 
     67           <li><code>a</code> is an applicative that takes zero arguments. If the call to
     68 <code>a</code> occurs within the dynamic extent of a call to <code>b</code>, then
     69 <code>a</code> returns the value of the first argument passed to <code>b</code> in
     70 the smallest enclosing dynamic extent of a call to <code>b</code>. If the
     71 call to <code>a</code> is not within the dynamic extent of any call to
     72 <code>b</code>, an error is signaled. 
     73 </ul>
     74         </p></blockquote></div>
     75 
     76 <h3 class="section">13.2 Keyed Static Variables</h3>
     77 
     78 <p><a name="index-keyed-static-variables-164"></a>  A keyed static variable is a device that binds data in an
     79 environment by a non-symbolic key, where the key is an accessor
     80 applicative. 
     81 <!-- add cf xref dynamic -->
     82 
     83 <div class="defun">
     84 &mdash; Applicative: <b>make-keyed-static-variable</b> (<var>make-keyed-static-variable</var>)<var><a name="index-make_002dkeyed_002dstatic_002dvariable-165"></a></var><br>
     85 <blockquote><p>  Returns a list of the form <code>(b a)</code>, where <code>b</code> and <code>a</code>
     86 are applicatives, as follows.  Each call to <code>make-keyed-static-variable</code>
     87 returns different <code>b</code> and <code>a</code>.
     88 
     89           <ul>
     90 <li><code>b</code> is an applicative that takes two arguments, the second of
     91 which must be an environment.  It constructs and returns a
     92 child-environment of its second argument, with initially no local
     93 bindings.
     94 
     95           <li><code>a</code> is an applicative that takes zero arguments. If the dynamic
     96 environment <code>e</code> of the call to a has an improper ancestor that
     97 was constructed by a call to <code>b</code>, then a returns the value of the
     98 first argument passed to <code>b</code> in the first such environment
     99 encountered by a depth-first traversal of the improper ancestors of
    100 <code>e</code>. If <code>e</code> has no improper ancestors constructed via
    101 <code>b</code>, an error is signaled. 
    102 </ul>
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