| 1 | <sect2><title>Contents of Bison-&bison-contversion;</title>
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| 2 |
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| 3 | <sect3><title>Program Files</title>
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| 4 |
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| 5 | <para>bison and yacc</para></sect3>
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| 6 |
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| 7 | <sect3><title>Descriptions</title>
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| 8 |
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| 9 | <sect4><title>bison</title>
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| 10 |
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| 11 | <para>bison is a parser generator, a replacement for yacc. yacc stands for Yet
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| 12 | Another Compiler Compiler. What is bison then? It is a program that
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| 13 | generates a program that analyzes the structure of a text file. Instead of
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| 14 | writing the actual program a user specifies how things should be connected
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| 15 | and with those rules a program is constructed that analyzes the
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| 16 | text file. There are a lot of examples where structure is needed and
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| 17 | one of them is the calculator.</para>
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| 18 |
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| 19 | <para>Given the string :</para>
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| 20 |
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| 21 | <blockquote><literallayout> 1 + 2 * 3</literallayout></blockquote>
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| 22 |
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| 23 | <para>A human can easily come to the result 7. Why? Because of the structure.
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| 24 | Our brain knows
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| 25 | how to interpret the string. The computer doesn't know that and bison is a
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| 26 | tool to help it understand by presenting the string in the following way
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| 27 | to the compiler:</para>
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| 28 |
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| 29 | <blockquote><literallayout> +
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| 30 | / \
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| 31 | * 1
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| 32 | / \
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| 33 | 2 3</literallayout></blockquote>
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| 34 |
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| 35 | <para>Starting at the bottom of a tree and coming across the numbers 2 and
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| 36 | 3 which are joined by the multiplication symbol, the computer
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| 37 | multiplies 2 and 3. The result of that multiplication is remembered and
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| 38 | the next thing that the computer sees is the result of 2*3 and the
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| 39 | number 1 which are joined by the add symbol. Adding 1 to the previous
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| 40 | result makes 7. In calculating the most complex calculations can be
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| 41 | broken down in this tree format and the computer just starts at the
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| 42 | bottom and works its way up to the top and comes with the correct
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| 43 | answer. Of course, bison isn't only used for calculators
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| 44 | alone.</para></sect4>
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| 45 |
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| 46 | <sect4><title>yacc</title>
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| 47 |
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| 48 | <para>We create a yacc script which calls bison using the -y option.
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| 49 | This is for compatibility purposes for programs which use yacc instead
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| 50 | of bison.</para></sect4>
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| 51 |
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| 52 | </sect3>
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| 53 |
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| 54 | </sect2>
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| 55 |
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