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58 lines
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58 lines
2.0 KiB
XML
<sect2><title>Contents of Bison</title>
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<para>Last checked against version &bison-contversion;.</para>
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<sect3><title>Program Files</title>
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<para>bison and yacc</para></sect3>
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<sect3><title>Descriptions</title>
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<sect4><title>bison</title>
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<para>bison is a parser generator, a replacement for yacc. yacc stands for Yet
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Another Compiler Compiler. What is bison then? It is a program that
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generates a program that analyzes the structure of a text file. Instead of
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writing the actual program a user specifies how things should be connected
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and with those rules a program is constructed that analyzes the
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text file. There are a lot of examples where structure is needed and
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one of them is the calculator.</para>
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<para>Given the string :</para>
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<blockquote><literallayout> 1 + 2 * 3</literallayout></blockquote>
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<para>A human can easily come to the result 7. Why? Because of the structure.
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Our brain knows
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how to interpret the string. The computer doesn't know that and bison is a
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tool to help it understand by presenting the string in the following way
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to the compiler:</para>
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<blockquote><literallayout> +
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/ \
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* 1
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/ \
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2 3</literallayout></blockquote>
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<para>Starting at the bottom of a tree and coming across the numbers 2 and
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3 which are joined by the multiplication symbol, the computer
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multiplies 2 and 3. The result of that multiplication is remembered and
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the next thing that the computer sees is the result of 2*3 and the
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number 1 which are joined by the add symbol. Adding 1 to the previous
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result makes 7. In calculating, the most complex calculations can be
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broken down in this tree format and the computer just starts at the
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bottom and works its way up to the top and comes with the correct
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answer. Of course, bison isn't only used for calculators
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alone.</para></sect4>
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<sect4><title>yacc</title>
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<para>We create a bash script called yacc which calls bison using the -y
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option. This is for compatibility purposes for programs which use yacc
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instead of bison.</para></sect4>
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</sect3>
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</sect2>
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