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📁 建立《编译原理网络课程》的目的不仅使学生掌握构造编译程序的原理和技术
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<font class="title2"><b>6.4.3 含有嵌套过程的词法作用域</b></font>         

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在Pascal过程中的一个名字a的非局部出现是在静态程序正文中的a的最近嵌套说明的作用域之内。图6.18的Pascal程序中 
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<br> 
        &nbsp;&nbsp;&nbsp;  (1) <b><font color="#0000FF">program</font></b> sort(input,output); <br>  
        &nbsp;&nbsp;&nbsp;  (2) <b>&nbsp;&nbsp;&nbsp;<font color="#0000FF">var</font></b> a:array[0..10］ of   
        integer； <br> 
        &nbsp;&nbsp;&nbsp;  (3) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x: integer；   
        <br> 
        &nbsp;&nbsp;&nbsp;  (4) <b>&nbsp;&nbsp;&nbsp;<font color="#0000FF">procedure</font></b> readarray； <br>  
        &nbsp;&nbsp;&nbsp;  (5) <b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<font color="#0000FF">var</font></b>  
        i: integer； <br>  
        &nbsp;&nbsp;&nbsp;  (6) <b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<font color="#0000FF">begin</font></b>...a...   
        <b><font color="#0000FF">end</font></b> {readarray}; <br>  
        &nbsp;&nbsp;&nbsp;  (7) <b>&nbsp;&nbsp;&nbsp;<font color="#0000FF">procedure</font></b> exchange（i,j:integer) <br> 
        &nbsp;&nbsp;&nbsp;  (8) <b>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<font color="#0000FF">begin</font></b>  
        <br> 
        &nbsp;&nbsp;&nbsp;  (9) &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;x:=   
        a[i] ；a[i]:=a[j];a[j]:=x <br>  
        &nbsp;&nbsp;&nbsp;  (10)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b><font color="#0000FF">end</font></b> {exchange}; <br>  
        &nbsp;&nbsp;&nbsp;  (11)&nbsp;&nbsp; <b><font color="#0000FF">procedure</font></b> quicksort(m,n: integer)；   
        <br> 
        &nbsp;&nbsp;&nbsp;  (12)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b><font color="#0000FF">var</font></b> k,v:integer; <br>   
        &nbsp;&nbsp;&nbsp;  (13)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b><font color="#0000FF">function</font></b> 
        partition(y,z: integer): integer； <br> 
        &nbsp;&nbsp;&nbsp;  (14)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
<b><font color="#0000FF">var</font></b> i,j: integer； <br>  
        &nbsp;&nbsp;&nbsp;  (15)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
<b><font color="#0000FF">begin</font></b> ...a...<br>  
        &nbsp;&nbsp;&nbsp; (16)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...v... 
        <br>
        &nbsp;&nbsp;&nbsp;  (17)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;...exchange(i,j)；...  
        <br> 
        &nbsp;&nbsp;&nbsp;  (18)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
<b><font color="#0000FF">end</font></b> {partition}; <br>  
        &nbsp;&nbsp;&nbsp;  (19)&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <b><font color="#0000FF">begin</font></b>...<b><font color="#0000FF">end</font></b>  
        { quicksort}; <br>  
        &nbsp;&nbsp;&nbsp;  (20)&nbsp;&nbsp; <b><font color="#0000FF">begin</font></b>…<b><font color="#0000FF">end</font></b> {sort｝。 <br>  
        &nbsp;&nbsp;&nbsp; </p> 
      <p align="left">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 
      <b>图6.18</b>带有嵌套过程的一个Pascal程序<br>
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的嵌套的过程定义由下面的锯齿状的排列指出： 
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sort <br> 
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; readarray <br>
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; exchange <br>
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; quicksort <br>
        &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; partition <br><br>
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在图6.18的第(15)行上的a的出现是在函数partition之中，它嵌套在过程quicksort之内。a的最近嵌套说明是在第(2)行，位于包括整个程序的过程中。最近嵌套规则也同样用于过程名字。如第（17）行的由partition 调用的过程exchange对于partition而言是非局部的。应用这个规则我们首先检查exchange是否在quicksort之内被定义，由于它不是，我们在主程序sort中找到了它。 
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