and. FINITE AUTOMATA. Class date : 12 August, 2013. Prepared by : . Karimgailiu. R . Panmei. Roll no. : 11CS10020. GROUP NO. : 9. Stream of input characters (source). State Transition Machine 1. ID: 218387
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TRANSITION DIAGRAM BASED LEXICAL ANALYZERandFINITE AUTOMATA
Class date : 12 August, 2013
Prepared by :
Karimgailiu
R
Panmei
Roll no. : 11CS10020
GROUP NO. : 9
Slide2Stream of input characters (source)
State Transition Machine 1
State Transition Machine 2
State Transition Machine 3
Token
Lex
Compiler
p
attern1 pattern 2 pattern 3
Slide3Simulating the transition machines
:
Input string :
x
1,
x
2
,
x
3
…… 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
Slide4Two 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
Slide5Approach 2
:
Parallel simulation
Simulate all transition diagrams in parallel
The machine stops when no match is found
Slide6Pattern
: Define based on regular expression
Lex
compiler
C Compiler
a.out
Pattern
a.out
Source code
tokens
generate state transition machines
NFA : Advantage
DFA : advantage
Slide7FINITE AUTOMATA
Recognize regular languages
Accepts or rejects a possible input string
Two types :
1. Non deterministic finite automata(NFA)
2. Deterministic finite automata(DFA)
Slide8NFA
Definition :
N={
Σ
, S,
s
o
,
F,
Δ
}
where
Σ
: set of input symbol
S : finite set of states
s
o
: start state
F : finite set of final states
Δ
: transition function (
S
×
Σ →
P
(
S
))
where P(S) is the power set of S
Slide9More about NFA
Given an input a, NFA allows to go from one state to a multiple state a aϵ-transition is allowed ϵ
Slide10DFA
Definition :
D
={
Σ
, S,
s
o ,
f
,
δ
}
where
Σ
: set of input symbol
S : finite set of states
s
o
: start state
F : finite set of final states
δ
: transition function
(δ :
S
×
Σ →
S
)
Slide11More on DFA
No ϵ-transition is allowed For a given input a, DFA allows to moves from one state to a single state a
Slide12Simulating DFA
Input :
- a string x
- DFA with start state
s
o
, accepting
states F and transition function
detect
Output :
“yes” if accepts and “no” if rejects
Slide13
Algorithm :
s=
s
o
;
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;
Slide14
THE END
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