Theoretical Aspects of Lexical Analysis/Exercise 6

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Compute the non-deterministic finite automaton (NFA) by using Thompson's algorithm. Compute the minimal deterministic finite automaton (DFA).
The alphabet is Σ = { a, b }. Indicate the number of processing steps for the given input string.

  • G = { aa, aaaa, a|b}, input string = aaabaaaaa

NFA

The following is the result of applying Thompson's algorithm.

NFA built by Thompson's algorithm
b)*abb(a

DFA

Determination table for the above NFA

{

Graphical representation of the DFA
b)*abb(a
DFA minimization tree
{{{2}}}

Input Analysis

In Input In+1 / Token
0 aaabaaaaa$ 1
1 aabaaaaa$ 3
3 abaaaaa$ 4
4 baaaaa$ error (backtracking)
3 abaaaaa$ T1 (aa)
0 abaaaaa$ 1
1 baaaaa$ T3 (a)
0 baaaaa$ 2
2 aaaaa$ T3 (b)
0 aaaaa$ 1
1 aaaa$ 3
3 aaa$ 4
4 aa$ 5
5 a$ T2 (aaaa)
0 a$ 1
1 $ T3 (a)

The input string aaabaaaaa is, after 16 steps, split into three tokens: T1 (corresponding to lexeme aa), T3 (a), T3 (b), T2 (aaaa), and T3 (a).