Automata on ruby - ruby

Question

I have the following Automata class:
class DFA
attr_accessor :start, :end, :transition
def initialize(options = {})
#start = options[:start]
#end = options[:end]
#transition = options[:transition]
end
def run(input)
current_state = #start
for i in input
current_state = #transition[current_state][i]
end
return true if #end.include? current_state
return false
end
end
if $PROGRAM_NAME == __FILE__
d = DFA.new(:start => :q1, :end => [:q2],
:transition =>
{ :q1 => {'0' => :q1, '1' => :q2},
:q2 => {'0' => :q3, '1' => :q2},
:q3 => {'0' => :q2, '1' => :q3}
})
puts d.run(['1','1','0','0'])
puts d.run(['1','1','0','0','0'])
puts d.run(['0','0','0'])
end
Output:
True
False
False
The problem is that i want this Automata to be able to 'eat' 'ANY OTHER' symbol. It would be like 'default' or 'else' action. For example:
{ :q1 => {'0' => :q1, 'ANY OTHER SYMBOL' => :q2},
So, it will be possible to write:
puts d.run(['1','1','0','a'])
and get 'True'. What are possible solutions? Thank you!
P.S. I have to write an Automata, which will be able to parse .INI files. May be it would be better not to write a class, but just to form my automata in 'case...when...when...else...' statement? What do you think?

Answer 1

You could define a special symbol:
class DFA
ANY = :any
And calculate the state based on it:
state = #transitions[state][step] || #transitions[state][DFA::ANY]
And use it defining DFA:
{'0' => :q1, '1' => :q2, DFA::ANY => :q2}
Complete example after refactoring:
class DFA
ANY = :any
attr_accessor :start, :end, :transitions
def initialize(options = {})
#start = options[:start]
#end = options[:end]
#transitions = options[:transitions]
end
def run(steps)
state = #start
steps.each do |step|
state = #transitions[state][step] || #transitions[state][DFA::ANY]
raise 'Unexpected Symbol' if state.nil?
end
#end.include? state
end
end
dfa = DFA.new start: :q1,
end: [:q2],
transitions: {
q1: {'0' => :q1, '1' => :q2, DFA::ANY => :q2},
q2: {'0' => :q3, '1' => :q2},
q3: {'0' => :q2, '1' => :q3}
}
puts dfa.run(['Q', '0', '0']) #=> true