Help/Libraries/JITLib/environments/LazyEnvir.html

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  26 <p class="p1"><span class="s1"><b>LazyEnvir</b></span><span class="s2"><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span></span><b>lazy environment</b></p>
  27 <p class="p2"><br></p>
  28 <p class="p1">superclass: EnvironmentRedirect</p>
  29 <p class="p2"><br></p>
  30 <p class="p1">Environment with deferred evaluation and default values.</p>
  31 <p class="p2"><br></p>
  32 <p class="p2"><br></p>
  33 <p class="p1"><b>put(key, val)</b><span class="Apple-tab-span"> </span><span class="Apple-tab-span">    </span>sets the value of the reference at <b>key</b></p>
  34 <p class="p1"><b>at(key)</b><span class="Apple-tab-span">       </span><span class="Apple-tab-span">    </span><span class="Apple-tab-span">    </span>returns a reference to the object at <b>key.</b><span class="Apple-converted-space"> </span></p>
  35 <p class="p2"><br></p>
  36 <p class="p3"><span class="s3">See also: <a href="../../../Collections/Environment.html">Environment</a>, <a href="EnvironmentRedirect.html">EnvironmentRedirect</a>, <a href="ProxySpace.html">ProxySpace</a></span>.</p>
  37 <p class="p1">General overview: <a href="../JITLib.html"><span class="s4">JITLib</span></a></p>
  38 <p class="p2"><br></p>
  39 <p class="p1">Consequently, calculations can be done with nonexisting objects which can then be assigned later.</p>
  40 <p class="p1">Per default, a LazyEnvir returns instances of <a href="Maybe.html"><span class="s4">Maybe</span></a>. See also <a href="../Patterns/Fdef.html"><span class="s4">Fdef</span></a>.</p>
  41 <p class="p4"><br></p>
  42 <p class="p4"><br></p>
  43 <p class="p5">// examples</p>
  44 <p class="p4"><br></p>
  45 <p class="p6">l = <span class="s5">LazyEnvir</span>.push;</p>
  46 <p class="p4"><br></p>
  47 <p class="p5">// default objects are created on access</p>
  48 <p class="p6">~a;<span class="Apple-converted-space"> </span></p>
  49 <p class="p5"><span class="s3">~a.value; </span>// defaults to 1</p>
  50 <p class="p4"><br></p>
  51 <p class="p5">// operations on placeholders</p>
  52 <p class="p6">(</p>
  53 <p class="p6">~c = ~a + ~b;</p>
  54 <p class="p4"><br></p>
  55 <p class="p6">~c.value;</p>
  56 <p class="p6">)</p>
  57 <p class="p4"><br></p>
  58 <p class="p4"><br></p>
  59 <p class="p5">// variables can be assigned later</p>
  60 <p class="p6">(</p>
  61 <p class="p6">~a = 800;</p>
  62 <p class="p6">~b = { 1.0.rand };</p>
  63 <p class="p4"><br></p>
  64 <p class="p6">~c.value;<span class="Apple-converted-space"> </span></p>
  65 <p class="p6">)</p>
  66 <p class="p4"><br></p>
  67 <p class="p4"><br></p>
  68 <p class="p5">// variables can be exchanged later</p>
  69 <p class="p6">(</p>
  70 <p class="p6">~b = { 1000.rand };<span class="Apple-converted-space"> </span></p>
  71 <p class="p6">~c.value;<span class="Apple-converted-space"> </span></p>
  72 <p class="p6">)</p>
  73 <p class="p4"><br></p>
  74 <p class="p4"><br></p>
  75 <p class="p5">// making pattern space using LazyEnvir</p>
  76 <p class="p4"><br></p>
  77 <p class="p6">a = <span class="s5">LazyEnvir</span>.new;</p>
  78 <p class="p6">a.proxyClass=<span class="s6">\PatternProxy</span>;</p>
  79 <p class="p4"><br></p>
  80 <p class="p6">a.push;</p>
  81 <p class="p4"><br></p>
  82 <p class="p6">~x = <span class="s5">Pseq</span>([1, 2, 30], 1);</p>
  83 <p class="p6">~y = <span class="s5">Pseq</span>([~x], <span class="s5">inf</span>);</p>
  84 <p class="p4"><br></p>
  85 <p class="p6">z = ~y.asStream;</p>
  86 <p class="p4"><br></p>
  87 <p class="p6">z.next;</p>
  88 <p class="p6">z.next;</p>
  89 <p class="p6">z.next;</p>
  90 <p class="p6">~x = <span class="s5">Pseq</span>([100, 2, 300], 1);</p>
  91 <p class="p6">z.next;</p>
  92 <p class="p6">z.next;</p>
  93 <p class="p6">z.next;</p>
  94 <p class="p4"><br></p>
  95 <p class="p6">a.pop;</p>
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