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67 lines
1.7 KiB
XML
67 lines
1.7 KiB
XML
<sect2>
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<title>Contents</title>
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<para>
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The Bison package contains the bison program.
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</para>
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</sect2>
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<sect2><title>Description</title>
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<para>
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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
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of
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writing the actual program a user specifies how things should be connected
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and with
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those rules a program is constructed that analyzes the text file.
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</para>
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<para>
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There are a lot of examples where structure is needed and one of them is
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the
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calculator.
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</para>
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<para>
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Given the string :
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</para>
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<blockquote><literallayout>
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1 + 2 * 3
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</literallayout></blockquote>
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<para>
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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
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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:
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</para>
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<blockquote><literallayout>
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+
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/ \
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* 1
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/ \
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2 3
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</literallayout></blockquote>
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<para>
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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 it's way up to the top and comes with the correct
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answer. Of course, Bison isn't only used for calculators alone.
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</para>
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</sect2>
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