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- <sect2>
- <title>Contents</title>
- <para>The Bison package contains the bison program.</para>
- </sect2>
- <sect2><title>Description</title>
- <para>Bison is a parser generator, a replacement for YACC. YACC stands for Yet
- Another Compiler Compiler. What is Bison then? It is a program that
- generates a program that analyzes the structure of a text file. Instead
- of
- writing the actual program a user specifies how things should be connected
- and with
- those rules a program is constructed that analyzes the text file.</para>
- <para>There are a lot of examples where structure is needed and one of them is
- the calculator.</para>
- <para>Given the string :</para>
- <blockquote><literallayout> 1 + 2 * 3</literallayout></blockquote>
- <para>A human can easily come to the result 7. Why? Because of the structure.
- Our brain knows
- how to interpret the string. The computer doesn't know that and Bison
- is a
- tool to help it understand by presenting the string in the following way
- to the compiler:</para>
- <blockquote><literallayout> +
- / \
- * 1
- / \
- 2 3</literallayout></blockquote>
- <para>Starting at the bottom of a tree and coming across the numbers 2 and
- 3 which are joined by the multiplication symbol, the computer
- multiplies 2 and 3. The result of that multiplication is remembered and
- the next thing that the computer sees is the result of 2*3 and the
- number 1 which are joined by the add symbol. Adding 1 to the previous
- result makes 7. In calculating the most complex calculations can be
- broken down in this tree format and the computer just starts at the
- bottom and works it's way up to the top and comes with the correct
- answer. Of course, Bison isn't only used for calculators alone.</para>
- </sect2>
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