transition diagram based lexical analyzer and finite automata
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TRANSITION DIAGRAM BASED LEXICAL ANALYZER and FINITE AUTOMATA. Class date : 12 August, 2013 Prepared by : Karimgailiu R Panmei Roll no. : 11CS10020 GROUP NO. : 9. State Transition Machine 1. Stream of input characters (source). State Transition Machine 2. Token.

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transition diagram based lexical analyzer and finite automata

TRANSITION DIAGRAM BASED LEXICAL ANALYZERandFINITE AUTOMATA

Class date : 12 August, 2013

Prepared by : Karimgailiu R Panmei

Roll no. : 11CS10020

GROUP NO. : 9

slide2
State Transition Machine 1

Stream of input characters (source)

State Transition Machine 2

Token

State Transition Machine 3

Lex Compiler

pattern1 pattern 2 pattern 3

slide3
Simulating the transition machines :

Input string : x1,x2 ,x3 …… x n

  • Scan the input using forward pointer
  • Machine accepts or rejects based on the transition function
  • Match the longest prefix of the input
  • If accepted, token is produced
slide4
Two approach to simulate the machine :

Approach 1 :

Sequential simulation

  • Sequentially simulate the transition machines
  • If the previous machine fails, reset the forward pointer
  • Start the next transition machine
slide5
Approach 2 :

Parallel simulation

  • Simulate all transition diagrams in parallel
  • The machine stops when no match is found
slide6
Lex compiler

generate state transition machines

NFA : Advantage

Pattern : Define based on regular expression

Pattern

C Compiler

a.out

tokens

Source code

a.out

DFA : advantage

slide7
FINITE AUTOMATA
  • Recognize regular languages
  • Accepts or rejects a possible input string
  • Two types :

1. Non deterministic finite automata(NFA)

2. Deterministic finite automata(DFA)

slide8
NFA

Definition :

N={ Σ, S, so , F, Δ}

where

Σ : set of input symbol

S : finite set of states

so : start state

F : finite set of final states

Δ : transition function (S × Σ → P(S))

where P(S) is the power set of S

more about nfa
More about NFA
  • Given an input a, NFA allows to go from one state to a multiple state

a

a

  • ϵ-transition is allowed

ϵ

slide10
DFA

Definition :

D={ Σ, S, so , f, δ}

where

Σ : set of input symbol

S : finite set of states

so : start state

F : finite set of final states

δ : transition function (δ : S × Σ → S)

more on dfa
More on DFA
  • No ϵ-transition is allowed
  • For a given input a, DFA allows to moves from one state to a single state

a

simulating dfa
Simulating DFA

Input :

- a string x

- DFA with start state so , accepting

states F and transition function

detect

Output :

“yes” if accepts and “no” if rejects

slide13
Algorithm :

s=so ;

c= read_next_char(); //read_next_char() returns the next

//character

while(c!=‘\0’)

{

s=detect(s,c);

c=read_next_char();

}

if(s ϵ F)

return yes;

else

return no;

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