SpinningVinyl / NFA-runner

A simple Java program to run non-deterministic final state automata (NFAs).

NFA runner

This simple Java application is intended for running non-deterministic finite automata (NFAs).

It can also run the same deterministic state automata (DFAs) as UDFA, since every DFA is also an NFA.

To run the application:

java net.prsv.nfa.NFA file

Where file is a file containing the description of the automaton.

NFA description file

The syntax of the NFA description file is very simple.

Comments

Lines beginning with # (hash sign) are comments:

# This is a comment

States

Line beginning with Q: (uppercase Q followed by a colon) lists all states of the NFA, separated by commas.

Q:q0,q1,q2,q3

Line beginning with S: (uppercase S followed by a colon) lists the initial states. The initial states should be already defined in the Q: line:

S:q0,q1

Line beginning with A: (uppercase A followed by a colon) lists the acceptance states of the NFA. The acceptance states should be already defined in the Q: line:

A:q2,q3

Alphabet

Line beginning with L: (uppercase L followed by a colon) lists all symbols in the alphabet on which the NFA operates.

L:a,b,c,d

Transitions

Transitions are defined in the following way: old_state,symbol->new_state1,new_state2,..., e.g.:

q0,d->q2,q3

Null transitions (epsilon-transitions) are defined as following: old_state->new_state1,new_state2,..., e.g.:

q0->q1,q3

Needless to say, all states and symbols should be already defined in the Q: and L: lines.

Examples

Consider the following NFA. It operates on the alphabet consisting of symbols (a,b) and accepts all words where b is the penultimate symbol (e.g. ba, aba, bbb, abbababababb etc.):

An NFA file describing this state machine would look like this:

# this NFA accepts all strings where b is the penultimate character, e.g. ba, aba, bbb, aaaabbbbaaaba etc.
Q: q0,q1,q2
L: a,b
S: q0
A: q2
q0,b->q0,q1
q0,a->q0
q1,a->q2
q1,b->q2

The following state machine recognises the string abab|abbb (that is, abab or abbb):

An NFA file describing this state machine would look like this:

# this NFA recognizes the string abab|abbb
Q:q0,q1,q2,q3,q4,q5,q6,q7,q8,q9,q10
L:a,b
S:q0
A:q5,q10
# null transitions
q0->q1,q6
# normal transitions
q1,a->q2
q2,b->q3
q3,a->q4
q4,b->q5
q6,a->q7
q7,b->q8
q8,b->q9
q9,b->q10