SIMPLE PARSER FOR C

BY-PRADEEP RAGAV(1RV12IS031)

-PUNITH KUMAR S(1RV12IS035)

Contents

Introduction Types of parser High level design Implementation Conclusion References

Introduction

PARSER Component of a

complier design.

Checks the syntax of the language.

Takes tokens as input and outputs the parse tree.

Types of parser

Top down parser One first looks at the

highest level of the parse tree and works down the parse tree.

Disadvantages dangling else problem.

Example:- LL parser

Types of parser

Bottom up parser It identifies and

processes the text's lowest-level small details first, before its mid-level structures, and leaving the highest-level overall structure to last.

Example:- SLR, LALR

Software requirements specification

SOFTWARE REQUIREMENTS: OPERATING SYSTEM: Ubuntu 14.04 COMPILER USED : GCC version 3.2.2  EDITOR: VI Editor version 6.1 PROGRAMMING LANGUAGE : GNU C, Lex

version 2.5.4 HARDWARE REQUIREMENTS:

MAIN PROCESSOR : Pentium IV (500MHz) RAM SIZE : 128 MB CACHE MEMORY:256KB  DISKETTE DRIVE:1.FFMB,3.5inches

High level design

DFD level 0

DFD level 1

High level design

DFD level 2

JFLAP THIN

software for experimenting with formal languages topics.

Here we use it get the shift reduce table for the given grammar.

Implementation

Programming language used: - C programming language. Because

Easier to understand There is no need for higher level language such

as C++, Java… since we do not need object oriented programming.

Platform used: Linux operating system. Since it is easier to use and it is easier to code

in this platform.

Implementation

Parser has four moves in our program.

Action[sm,a]=shift s, parser will execute shift move.

Action[sm,a]=reduce r, parser will execute reduce move.

Action[sm,a]=acc(r0), input is accepted. Parsing is complete.

Action[sm,a]=error. Parser as encountered a error.

Implementation

Algorithm :-Shift_reduce_operation(char a, int t) Input: char a, int t Output: stack If(action[s, a]=shift s)

Push t on to the stackLet a be the next input symbol

Else if(action[s, a]=reduce a->b)Pop(b); symbols of the stack.Push(a);Let t be top of the stack.

Else if(action[s, a]=acc)Input is accepted;

Conclusion

Advantages The program can be directly entered or the filename

of the source code can be given as input.

Future scope The parser must be capable of parsing the entire

source code. The implemented parser exits on encountering the first error.

Displaying appropriate error messages. Error handling and recovery strategies can be implemented.

Identifying the number of format specifiers and matching the data types with the variable type in printf and scanf statements.

References

[1] Alfred W Aho, Monica S Lam, Ravi Sethi, Jeffrey D Ullman, Compilers Principles, Techniques and Tools, Pearson Education, 2008. 

[2] Leland L. Beck, System Software, Third Edition, Addison-Wesley, 1997.