pl.htm

清华教材后面的pl0程序

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style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>分程序语法描述图</span></span></p>

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style='mso-bookmark:_Toc26728276'><span lang=EN-US><!--[if gte vml 1]><v:shape
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style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>语句语法描述</span></span></p>

<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span lang=EN-US><!--[if gte vml 1]><v:shape
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<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>条件语句描述图</span></span></p>

<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span lang=EN-US><!--[if gte vml 1]><v:shape
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<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>表达式语法描述</span></span></p>

<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span lang=EN-US><!--[if gte vml 1]><v:shape
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<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>项语法描述</span></span></p>

<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span lang=EN-US><!--[if gte vml 1]><v:shape
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<p class=MsoNormal align=center style='text-align:center'><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>因子语法描述</span></span></p>

<h2><span style='mso-bookmark:_Toc26728276'><a name="_Toc26728275"><span
lang=EN-US>1</span></a></span><span style='mso-bookmark:_Toc26728276'><span
style='mso-bookmark:_Toc26728275'><span style='font-family:黑体;mso-ascii-font-family:
Arial'>、</span><span lang=EN-US>PL/0</span></span></span><span
style='mso-bookmark:_Toc26728276'><span style='mso-bookmark:_Toc26728275'><span
style='font-family:黑体;mso-ascii-font-family:Arial'>语言文法的</span><span
lang=EN-US>EBNF</span></span></span><span style='mso-bookmark:_Toc26728276'><span
style='mso-bookmark:_Toc26728275'><span style='font-family:黑体;mso-ascii-font-family:
Arial'>（巴克斯</span><span lang=EN-US>-</span></span></span><span
style='mso-bookmark:_Toc26728276'><span style='mso-bookmark:_Toc26728275'><span
style='font-family:黑体;mso-ascii-font-family:Arial'>瑙尔范式）表示</span></span></span></h2>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈表达式〉</span><span lang=EN-US>::=[+|-]</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈项〉</span><span
lang=EN-US>{</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈加法运算符〉〈项〉</span><span lang=EN-US>}</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈项〉</span><span lang=EN-US>::=</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈因子〉</span><span
lang=EN-US>{</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈乘法运算符〉〈因子〉</span><span lang=EN-US>}</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈因子〉</span><span lang=EN-US>::=</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈标识符〉</span><span
lang=EN-US>|</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈无符号整数〉</span><span lang=EN-US>|</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>‘（’〈表达式〉‘）’</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈加法运算符〉</span><span lang=EN-US>::=+|-</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈乘法运算符〉</span><span lang=EN-US>::=*|/</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈关系运算符〉</span><span lang=EN-US>::==|#|&lt;|&lt;=|&gt;|&gt;=</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈条件语句〉</span><span lang=EN-US>::=IF</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈条件〉</span><span
lang=EN-US>THEN</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈语句〉</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈过程调用语句〉</span><span lang=EN-US>::=CALL</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈标识符〉</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈当型循环语句〉</span><span lang=EN-US>::=WHILE</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>〈条件〉</span><span
lang=EN-US>DO</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈语句〉</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈读语句〉</span><span lang=EN-US>::=READ</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>‘（’〈标识符〉</span><span
lang=EN-US>{</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>，〈标识符〉</span><span lang=EN-US>}</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>‘）’</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈写语句〉</span><span lang=EN-US>::=WRITE</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>‘（’〈表达式〉</span><span
lang=EN-US>{</span></span><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>，〈表达式〉</span><span lang=EN-US>}</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:宋体;mso-ascii-font-family:
"Times New Roman";mso-hansi-font-family:"Times New Roman"'>‘）’</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈字母〉</span><span lang=EN-US>::=a|b|…|X|Y|Z</span></span></p>

<p class=MsoNormal><span style='mso-bookmark:_Toc26728276'><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>〈数字〉</span><span lang=EN-US>::=0|1|…|8|9</span></span></p>

<h2><span style='mso-bookmark:_Toc26728276'><span lang=EN-US>2</span></span><span
style='mso-bookmark:_Toc26728276'><span style='font-family:黑体;mso-ascii-font-family:
Arial'>、</span><span lang=EN-US>PL/0</span></span><span style='mso-bookmark:
_Toc26728276'><span style='font-family:黑体;mso-ascii-font-family:Arial'>编译程序的结构</span></span></h2>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>PL/0</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语言可以看成</span><span lang=EN-US>PASCAL</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语言的子集，它的编译程序是一个编译解释执行系统。</span><span lang=EN-US>PL/0</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的目标程序为假想栈式计算机的汇编语言，与具体计算机无关。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span lang=EN-US>PL/0</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>的编译程序和目标程序的解释执行程序都是用</span><span lang=EN-US>PASCAL</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语言书写的，因此</span><span lang=EN-US>PL/0</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语言可在配备</span><span lang=EN-US>PASCAL</span><span
style='font-family:宋体;mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:
"Times New Roman"'>语言的任何机器上实现。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>其编译过程采用一趟扫描方式，以语法分析程序为核心，词法分析和代码生成程序都作为一个独立的过程，当语法分析需要读单词时就调用词法分析程序，而当语法分析正确需要生成相应的目标代码时，则调用代码生成程序。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>用表格管理程序建立变量、常量和过程表示符的说明与引用之间的信息联系。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>用出错处理程序对词法和语法分析遇到的错误给出在源程序中出错的位置和错位性质。</span></p>

<p class=MsoNormal style='text-indent:21.0pt'><span style='font-family:宋体;
mso-ascii-font-family:"Times New Roman";mso-hansi-font-family:"Times New Roman"'>当源程序编译正确时，</span><span
lang=EN-US>PL/0</span><span style='font-family:宋体;mso-ascii-font-family:"Times New Roman";