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