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77 lines
2.6 KiB
Go
77 lines
2.6 KiB
Go
package main
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const EPSILON int = 0
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type State struct {
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content int // Contents of current state
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isEmpty bool // If it is empty - Union operator and Kleene star states will be empty
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isLast bool // If it is the last state (acept state)
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output []*State // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
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transitions map[int][]*State // Transitions to different states (maps a character (int representation) to a _list of states. This is useful if one character can lead multiple states eg. ab|aa)
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isKleene bool // Identifies whether current node is a 0-state representing Kleene star
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}
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type NFA struct {
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start State
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outputs []State
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}
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// verifyLastStatesHelper performs the depth-first recursion needed for verifyLastStates
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func verifyLastStatesHelper(state *State, visited map[*State]bool) {
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if len(state.transitions) == 0 {
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state.isLast = true
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return
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}
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if len(state.transitions) == 1 && len(state.transitions[state.content]) == 1 && state.transitions[state.content][0] == state { // Eg. a*
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state.isLast = true
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return
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}
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if len(state.transitions) == 1 && state.isKleene { // A State representing a Kleene Star has a transition going out, which loops back to it. If that is the only transition (and it contains only one state), then it must be a last-state
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for _, v := range state.transitions { // Should only loop once
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if len(v) == 1 {
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state.isLast = true
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return
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}
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}
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}
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if visited[state] == true {
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return
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}
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visited[state] = true
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for _, states := range state.transitions {
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for i := range states {
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if states[i] != state {
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verifyLastStatesHelper(states[i], visited)
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}
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}
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}
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}
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// verifyLastStates enables the 'isLast' flag for the leaf nodes (last states)
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func verifyLastStates(start []*State) {
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verifyLastStatesHelper(start[0], make(map[*State]bool))
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}
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func concatenate(s1 *State, s2 *State) *State {
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for i := range s1.output {
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s1.output[i].transitions[s2.content] = append(s1.output[i].transitions[s2.content], s2)
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}
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s1.output = s2.output
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return s1
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}
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func kleene(s1 State) *State {
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toReturn := &State{}
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toReturn.transitions = make(map[int][]*State)
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toReturn.content = EPSILON
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toReturn.isEmpty = true
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toReturn.isKleene = true
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toReturn.output = append(toReturn.output, toReturn)
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for i := range s1.output {
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s1.output[i].transitions[toReturn.content] = append(s1.output[i].transitions[toReturn.content], toReturn)
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}
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toReturn.transitions[s1.content] = append(toReturn.transitions[s1.content], &s1)
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return toReturn
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}
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