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Pune Vidyarthi Griha’s

COLLEGE OF ENGINEERING, NASHIK.

“ LANGUAGE TRANSLATOR ”

By

Prof. Anand N. Gharu (Assistant Professor)

PVGCOE Computer Dept.

22nd Jan 2018 .

CONTENTS :-

1. Role of lexical analysis

2. Parsing, token, pattern, lexemes lex. Error

3. Regular def. for language construct & string

4. Sequences, comments & transition diagram for

recognition of tokens, reserved word & ident.

5. Introduction to Compiler & Interpreters

6. General model of Compiler

7. Compare compiler and interpreter

8. Use of interpreter & component of interpreter

9. Overview of Lex & YACC Specifications.

3

What’s a compiler? • All computers only understand machine language

• Therefore, high-level language instructions must be translated into machine language prior to execution

10000010010110100100101……

This is

a program

4

What’s a compiler? • Compiler

A piece of system software that translates high-level languages into machine language

10000010010110100100101……

Congrats!

while (c!='x')

{

if (c == 'a' || c == 'e' || c == 'i')

printf("Congrats!");

else

if (c!='x')

printf("You Loser!");

}

Compiler

gcc -o prog program.c

program.c

prog

Compiler • Complier:-

• These are the system programs which will

automatically translate the High level language

program in to the machine language program

Source program High level Lang. Prog.

Target program / M/C Lang. Prog.

Compiler

Database

Types of Compiler • Cross Assembler:-

• These are the system programs which will automatically

translate the Assembly Language program compatible with

M/C A, in to the machine language program compatible with

M/C A

Cross Assembler

Source program Assembly Lang. Prog. Compatible with M/C A

Target program / M/C Lang. Prog. Compatible with M/C A

M/C B

Types of compiler • Cross Compiler:-

• These are the system programs which will automatically

translate the HLL program compatible with M/C A, in to the

machine language program compatible with M/C A , but the

underlying M/C is M/C B

Cross Compiler

Source program

HLL Prog. Compatible with M/C A

Target program / M/C Lang. Prog.

M/C B

Types of Compiler

Interpreter - It is the language translator which execute source program line by line with out translating them into machine language.

- It does not generate object code.

Compiler vs Interpreter

, C++ , Visual Basic

Phases of compiler

13

• Any compiler must perform two major tasks

o Analysis of the source program

o Synthesis of a machine-language program

Structure of Compiler

Compiler

Analysis Synthesis


14

Scanner Parser Semantic

Routines

Code

Generator

Optimizer

Source

Program Tokens Syntactic

Structure

Symbol and

Attribute

Tables

(Used by all Phases of The Compiler)

(Character Stream)

Intermediate

Representation

Target machine code


15


Routines

Code

Generator

Optimizer

Source


Structure

Symbol and

Attribute

Tables

(Used by all

Phases of

The Compiler)

Scanner (Lexical Analysis) The scanner begins the analysis of the source program

by reading the input, character by character, and

grouping characters into individual words and symbols (tokens)

RE ( Regular expression )

NFA ( Non-deterministic Finite Automata )

DFA ( Deterministic Finite Automata )

LEX

(Character Stream)

Intermediate

Representation

Target machine code


16


Routines

Code

Generator

Optimizer

Source


Structure

Symbol and

Attribute

Tables

(Used by all

Phases of

The Compiler)

Parser (Syntax Analysis) Given a formal syntax specification (typically as a

context-free grammar [CFG] ), the parse reads tokens and groups them into units as specified by the productions of the CFG being used.

As syntactic structure is recognized, the parser either calls corresponding semantic routines directly or builds a syntax tree.

CFG ( Context-Free Grammar )

BNF ( Backus-Naur Form )

GAA ( Grammar Analysis Algorithms )

LL, LR, SLR, LALR Parsers

YACC

(Character Stream)

Intermediate

Representation

Target machine code


17


Routines

Code

Generator

Optimizer

Source

Program

(Character Stream)

Tokens Syntactic

Structure

Intermediate

Representation

Symbol and

Attribute

Tables

(Used by all

Phases of

The Compiler)

Semantic Routines Perform two functions

Check the static semantics of each construct

Do the actual translation

The heart of a compiler

Syntax Directed Translation

Semantic Processing Techniques

IR (Intermediate Representation) Target machine code


18


Routines

Code

Generator

Optimizer

Source


Structure

Symbol and

Attribute

Tables

(Used by all

Phases of

The Compiler)

Optimizer The IR code generated by the semantic routines is

analyzed and transformed into functionally equivalent but improved IR code

This phase can be very complex and slow

Peephole optimization

loop optimization, register allocation, code scheduling

Register and Temporary Management

Peephole Optimization

(Character Stream)

Intermediate

Representation

Target machine code


19

Source

Program

(Character Stream)

Scanner Tokens

Parser Syntactic

Structure

Semantic

Routines

Intermediate

Representation

Optimizer

Code

Generator

Code Generator Interpretive Code Generation

Generating Code from Tree/Dag

Grammar-Based Code Generator

Target machine code


20

Scanner [Lexical Analyzer]

Parser [Syntax Analyzer]

Semantic Process [Semantic analyzer]

Code Generator

[Intermediate Code Generator]

Code Optimizer

Tokens

Parse tree

Abstract Syntax Tree w/ Attributes

Non-optimized Intermediate Code

Optimized Intermediate Code

Code Optimizer

Target machine code

Lexical Analysis

Syntax Analysis

Semantic Analysis

Intermediate Code Generation

Code Optimization

Code Generation

Code Optimization


Compiler writing tools

• Compiler generators or compiler-

compilers

oE.g. scanner and parser

generators

oExamples : Yacc, Lex

52

Overview of Lex & YAAC

Lex:

Theory.

Execution.

Example.

Yacc:

Theory.

Description.

Example.

Lex & Yacc linking.

Demo.

53

Lex

lex is a program (generator) that generates lexical analyzers, (widely

used on Unix).

It is mostly used with Yacc parser generator.

Written by Eric Schmidt and Mike Lesk.

It reads the input stream (specifying the lexical analyzer ) and

outputs source code implementing the lexical analyzer in the C

programming language.

Lex will read patterns (regular expressions); then produces C code

for a lexical analyzer that scans for identifiers.

54

STRUCTURE OF LEX

Lex

◦ A simple pattern: letter(letter|digit)*

Regular expressions are translated by lex to a computer

program that mimics an FSA.

This pattern matches a string of characters that begins with a

single letter followed by zero or more letters or digits.

56

Lex

Some limitations, Lex cannot be used to recognize nested

structures such as parentheses, since it only has states and

transitions between states.

So, Lex is good at pattern matching, while Yacc is for more

challenging tasks. 57

Lex

Pattern Matching Primitives

58

Lex

• Pattern Matching examples.

59

Lex ……..Definitions section……

%%

……Rules section……..

%%

……….C code section (subroutines)……..

• The input structure to Lex.

•Echo is an action and

predefined macro in lex that

writes code matched by the

pattern.

60

Lex

Lex predefined variables.

61

Lex

Whitespace must separate the defining term and the associated expression.

Code in the definitions section is simply copied as-is to the top of the generated

C file and must be bracketed with “%{“ and “%}” markers.

substitutions in the rules section are surrounded by braces ({letter}) to

distinguish them from literals. 62

Yacc Theory:

◦ Yacc reads the grammar and generate C code for a parser .

◦ Grammars written in Backus Naur Form (BNF) .

◦ BNF grammar used to express context-free languages .

◦ e.g. to parse an expression , do reverse operation( reducing the

expression)

◦ This known as bottom-up or shift-reduce parsing .

◦ Using stack for storing (LIFO).

63

STRUCTURE OF YACC

Yacc

• Input to yacc is divided into three sections.

... definitions ...

%%

... rules ...

%%

... subroutines ...

65

Yacc

The definitions section consists of:

◦ token declarations .

◦ C code bracketed by “%{“ and

“%}”.

◦ the rules section consists of:

BNF grammar .

the subroutines section consists of:

◦ user subroutines .

66

yacc& lex in Together

• The grammar:

program -> program expr | ε

expr -> expr + expr | expr - expr | id

• Program and expr are nonterminals.

• Id are terminals (tokens returned by lex) .

• expression may be :

o sum of two expressions .

o product of two expressions .

o Or an identifiers

67

Lex file

68

Yacc file

69

Linking lex&yacc

70

Thank You

1/22/2018 71

[email protected]

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