Yacc/MiS Programming Tutorial53

Yacc (Yet Another Compiler Compiler) and MiS (Morpho Syntax) are tools for generating parsers. A parser is a program that takes an input stream and produces a tree that represents the structure of the input. Parsers are used in many different applications, such as compilers, interpreters, and text editors.

Yacc is a parser generator that is written in the C programming language. It takes a grammar specification as input and produces a C program that can be compiled into a parser. The grammar specification is a set of rules that define the structure of the input stream. The C program that is produced by Yacc is a LALR(1) parser, which is a type of parser that is efficient and easy to implement.

MiS is a parser generator that is written in the Java programming language. It takes a grammar specification as input and produces a Java program that can be compiled into a parser. The grammar specification is a set of rules that define the structure of the input stream. The Java program that is produced by MiS is a GLR parser, which is a type of parser that is more powerful than a LALR(1) parser but is also more difficult to implement.

In this tutorial, we will show you how to use Yacc and MiS to generate parsers. We will start by introducing the basic concepts of parsing and then we will show you how to write grammar specifications for Yacc and MiS. Finally, we will show you how to compile and run the parsers that you have generated.

Parsing

Parsing is the process of taking an input stream and producing a tree that represents the structure of the input. The tree that is produced by a parser is called a parse tree. The parse tree can be used to perform a variety of tasks, such as checking the validity of the input, translating the input into another language, or executing the input as a program.

There are many different types of parsers. The most common type of parser is a top-down parser. A top-down parser starts at the root of the parse tree and works its way down to the leaves. As it descends the tree, the parser checks the input stream to make sure that it matches the structure of the tree. If the input stream does not match the structure of the tree, the parser reports an error.

Another common type of parser is a bottom-up parser. A bottom-up parser starts at the leaves of the parse tree and works its way up to the root. As it ascends the tree, the parser combines the leaves into larger and larger nodes until it reaches the root. If the input stream does not match the structure of the tree, the parser reports an error.

Yacc

Yacc is a parser generator that is written in the C programming language. It takes a grammar specification as input and produces a C program that can be compiled into a parser. The grammar specification is a set of rules that define the structure of the input stream. The C program that is produced by Yacc is a LALR(1) parser, which is a type of parser that is efficient and easy to implement.

To use Yacc, you first need to write a grammar specification. The grammar specification is a set of rules that define the structure of the input stream. The rules are written in a special language that is called Yacc grammar. The following is an example of a Yacc grammar specification for a simple calculator:```
%token NUMBER
%token PLUS
%token MINUS
%token TIMES
%token DIVIDE
%%
expression: expression PLUS expression
| expression MINUS expression
| expression TIMES expression
| expression DIVIDE expression
| NUMBER
```

This grammar specification defines a set of rules for parsing arithmetic expressions. The first rule states that an expression can be composed of two expressions that are separated by a plus sign. The second rule states that an expression can be composed of two expressions that are separated by a minus sign. The third rule states that an expression can be composed of two expressions that are separated by a multiplication sign. The fourth rule states that an expression can be composed of two expressions that are separated by a division sign. The fifth rule states that an expression can be a single number.

Once you have written a grammar specification, you can use Yacc to generate a C program that can be compiled into a parser. The following command generates a C program for the calculator grammar specification:```
yacc -d calculator.y
```

The -d option tells Yacc to generate a parser that is capable of producing debugging information. The calculator.y file is the input file that contains the grammar specification.

The output of the yacc command is a C program that is called calculator.c. The calculator.c program can be compiled into a parser using the following command:```
gcc -o calculator calculator.c
```

The calculator program is a LALR(1) parser that can be used to parse arithmetic expressions. The parser can be used to check the validity of arithmetic expressions, translate arithmetic expressions into another language, or execute arithmetic expressions as programs.

MiS

2025-01-03

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