Allow one state to map to multiple states with the same transition eg. ab|aa
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21
main.go
21
main.go
@@ -106,7 +106,7 @@ func thompson(re string) State {
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for _, c := range re {
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if isAlphaNum(c) {
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state := State{}
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state.transitions = make(map[int]*State)
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state.transitions = make(map[int][]*State)
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state.content = int(c)
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state.output = make([]*State, 0)
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state.output = append(state.output, &state)
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@@ -119,14 +119,14 @@ func thompson(re string) State {
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s2 := pop(&nfa)
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s1 := pop(&nfa)
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for i := range s1.output {
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s1.output[i].transitions[s2.content] = &s2
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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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nfa = append(nfa, s1)
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case '*':
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s1 := pop(&nfa)
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for i := range s1.output {
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s1.output[i].transitions[s1.content] = &s1
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s1.output[i].transitions[s1.content] = append(s1.output[i].transitions[s1.content], &s1)
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}
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// Reset output to s1 (in case s1 was a union operator state, which has multiple outputs)
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s1.output = nil
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@@ -136,10 +136,10 @@ func thompson(re string) State {
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s1 := pop(&nfa)
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s2 := pop(&nfa)
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s3 := State{}
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s3.transitions = make(map[int]*State)
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s3.transitions = make(map[int][]*State)
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s3.output = append(s3.output, &s1, &s2)
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s3.transitions[s1.content] = &s1
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s3.transitions[s2.content] = &s2
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s3.transitions[s1.content] = append(s3.transitions[s1.content], &s1)
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s3.transitions[s2.content] = append(s3.transitions[s2.content], &s2)
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s3.content = UNION
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s3.isEmpty = true
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@@ -159,12 +159,11 @@ func thompson(re string) State {
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func main() {
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var re string
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// fmt.Scanln(&re)
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re = "a(b|c)*d"
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re = "abab|abbb"
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re_postfix := shuntingYard(re)
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fmt.Println(re_postfix)
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start := thompson(re_postfix)
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assert(len(start.transitions) == 1)
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assert(len(start.transitions[UNION].transitions) == 2)
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UNUSED(start)
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}
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func UNUSED[T any](val T) {}
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20
nfa.go
20
nfa.go
@@ -3,11 +3,11 @@ 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 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 (can be associated with an int, representing content of destination state)
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content int // Contents of current state
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isEmpty bool // If it is empty - Union operator 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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}
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type NFA struct {
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@@ -21,7 +21,7 @@ func verifyLastStatesHelper(state *State, visited map[*State]bool) {
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state.isLast = true
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return
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}
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if state.transitions[state.content] == state { // Eg. a*
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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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@@ -29,9 +29,11 @@ func verifyLastStatesHelper(state *State, visited map[*State]bool) {
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return
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}
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visited[state] = true
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for k := range state.transitions {
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if state.transitions[k] != state {
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verifyLastStatesHelper(state.transitions[k], visited)
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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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