regex/nfa.go

package main

const EPSILON int = 0

type State struct {
	content     int            // Contents of current state
	isEmpty     bool           // If it is empty - Union operator states will be empty
	isLast      bool           // If it is the last state (acept state)
	output      []*State       // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
	transitions map[int]*State // Transitions to different states (can be associated with an int, representing content of destination state)
}

type NFA struct {
	start   State
	outputs []State
}

// verifyLastStatesHelper performs the depth-first recursion needed for verifyLastStates
func verifyLastStatesHelper(state *State, visited map[*State]bool) {
	if len(state.transitions) == 0 {
		state.isLast = true
		return
	}
	if visited[state] == true {
		return
	}
	visited[state] = true
	for k := range state.transitions {
		if state.transitions[k] != state {
			verifyLastStatesHelper(state.transitions[k], visited)
		}
	}
}

// verifyLastStates penables the 'isLast' flag for the leaf nodes (last states)
func verifyLastStates(start []State) {
	verifyLastStatesHelper(&start[0], make(map[*State]bool))
}