The document explains the concepts of parsers and compilers in computer science, emphasizing that a parser evaluates scripts to determine their grammatical correctness by breaking them into tokens and producing a hierarchical data structure, typically a tree. It distinguishes between parsing and evaluating, noting that parsers do not execute code or summarize text but are essential in the compilation process. It also describes the phases of a compiler, particularly focusing on lexical analysis and syntax analysis.

1. Parser
DEFINITION AND SOME KEY POINTS

2. Definition
 A computer program use just to evaluate scripts according
to the respective grammar.
 In computer Science, its a text analyzing process to
determine if it belongs to a certain language or not.
 Mostly used as a part of High-Level-Language
translators(Interpreter or Compiler).
 But some Standalone Parsers are available for specific
purposes.(for e.g. http://nlp.stanford.edu/software/lex-parser.shtml)

3. What and How it works?
 It first receives input in the form of
 sequential source program or
 Stream of characters (String).
 Break them into small chunks or parts (tokens).
 For Example in English Language:
He is running to school
Subject Verb Object
 And produces a data-structure that is usually a tree.

4. What is not Parsing?
 Parser does not evaluate one thing into another. If
just change its representation from one form to
another.
 Parser is not responsible for summarizing or extract
the original body of text.
Word Processing Programs also uses a parser to check
spelling and grammatical mistakes.

5. But What is Compiler ???
Compiler is a Language Translator or a
computer program that translates a Human
understandable instruction set into Computer
understandable form
Or simply, the output of compiler is .exe file,
Object code or RTL(Register Transfer Language)

6. Compiler VS Parser
 From the previous discussion it can be concluded
that:
 The output of Parser is a Data-Structure that is useless for the
for both Liveware and hardware.
 But this will be a very useful input for some component of the
compiler.
 Whereas, the output of the compiler is understandable and can
be executed by Computer hardware

7. Phases of Compiler

8. Phases of Compiler
These 3 phases can
be called as they
are actually
parsing the source
Program

9. Lexical Analysis
 As the name shows, Its done by Lexical Analyzer.
 Reads the characters from the input stream or source
program.
 Group them in tokens.
 Each token describe some important element.
 CONFUSED….!!!
 Lets see an exmaple.

10. Token Example
 int a = 10 ;
 That’s the code for declaring and initializing a variable “a”.
 When this LOC passed through t Lexical Box following
thing happens
Identifier Constant
int a = 10 ;
Data Type Assignment Symbol
Operator
 Each of this term is called as Token.
 For e.g. “a” is a token of “Identifier type”.
 The Character Sequence “int” is called as the its Lexeme.
http://en.wikipedia.org/wiki/Token_(parser)#Token

11. Can we proceed further OR

12. Syntax Analyzer
 According to many sources, this phase is actually
responsible for Parsing.
 So, the input of this phase is the Tokens formed in
the previous phase i.e. Lexical Analysis.
 In this phase, the recently formed token acquire a
Hierarchical Data Structure, that’s called Tree in
Computer Science.

13. Before Moving Further
 First Explore this New Buzz Word Tree.
 Definition: Its an hierarchical Data Structure that is
also known as the Collection of some related nodes.

14. Terminologies
 Node is structure that contains some value or
condition.
 In the tree on right side
 “2” is a parent node that has two
child nodes “7” and “5”.