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301 lines
11 KiB
Go
301 lines
11 KiB
Go
package main
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import (
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"slices"
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)
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const EPSILON int = 0
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type assertType int
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const (
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NONE assertType = iota
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SOS
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EOS
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WBOUND
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NONWBOUND
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PLA // Positive lookahead
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NLA // Negative lookahead
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PLB // Positive lookbehind
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NLB // Negative lookbehind
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)
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type State struct {
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content stateContents // 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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assert assertType // Type of assertion of current node - NONE means that the node doesn't assert anything
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zeroMatchFound bool // Whether or not the state has been used for a zero-length match - only relevant for zero states
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allChars bool // Whether or not the state represents all characters (eg. a 'dot' metacharacter). A 'dot' node doesn't store any contents directly, as it would take up too much space
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except []rune // Only valid if allChars is true - match all characters _except_ the ones in this block. Useful for inverting character classes.
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lookaroundRegex string // Only for lookaround states - Contents of the regex that the lookaround state holds
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lookaroundNFA *State // Holds the NFA of the lookaroundRegex - if it exists
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lookaroundNumCaptureGroups int // Number of capturing groups if current node is a lookaround
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groupBegin bool // Whether or not the node starts a capturing group
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groupEnd bool // Whether or not the node ends a capturing group
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groupNum int // Which capturing group the node starts / ends
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}
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// Clones the NFA starting from the given state.
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func cloneState(start *State) *State {
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return cloneStateHelper(start, make(map[*State]*State))
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}
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// Helper function for clone. The map is used to keep track of which states have
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// already been copied, and which ones haven't.
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// This function was created using output from Llama3.1:405B.
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func cloneStateHelper(state *State, cloneMap map[*State]*State) *State {
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// Base case - if the clone exists in our map, return it.
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if clone, exists := cloneMap[state]; exists {
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return clone
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}
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if state == nil {
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return nil
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}
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// Recursive case - if the clone doesn't exist, create it, add it to the map,
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// and recursively call for each of the transition states.
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clone := &State{
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content: append([]int{}, state.content...),
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isEmpty: state.isEmpty,
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isLast: state.isLast,
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output: make([]*State, len(state.output)),
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transitions: make(map[int][]*State),
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isKleene: state.isKleene,
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assert: state.assert,
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zeroMatchFound: state.zeroMatchFound,
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allChars: state.allChars,
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except: append([]rune{}, state.except...),
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lookaroundRegex: state.lookaroundRegex,
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groupEnd: state.groupEnd,
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groupBegin: state.groupBegin,
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groupNum: state.groupNum,
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}
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cloneMap[state] = clone
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for i, s := range state.output {
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if s == state {
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clone.output[i] = clone
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} else {
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clone.output[i] = cloneStateHelper(s, cloneMap)
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}
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}
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for k, v := range state.transitions {
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clone.transitions[k] = make([]*State, len(v))
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for i, s := range v {
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if s == state {
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clone.transitions[k][i] = clone
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} else {
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clone.transitions[k][i] = cloneStateHelper(s, cloneMap)
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}
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}
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}
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if state.lookaroundNFA == state {
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clone.lookaroundNFA = clone
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}
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clone.lookaroundNFA = cloneStateHelper(state.lookaroundNFA, cloneMap)
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return clone
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}
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// Checks if the given state's assertion is true. Returns true if the given
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// state doesn't have an assertion.
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func (s State) checkAssertion(str []rune, idx int) bool {
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if s.assert == SOS {
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return idx == 0
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}
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if s.assert == EOS {
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// Index is at the end of the string, or it points to the last character which is a newline
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return idx == len(str) || (idx == len(str)-1 && str[len(str)-1] == '\n')
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}
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if s.assert == WBOUND {
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return isWordBoundary(str, idx)
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}
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if s.assert == NONWBOUND {
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return !isWordBoundary(str, idx)
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}
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if s.isLookaround() {
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// The process here is simple:
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// 1. Compile the regex stored in the state's contents.
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// 2. Run it on the test string.
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// 3. Based on the kind of lookaround (and the indices we get), determine what action to take.
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startState := s.lookaroundNFA
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matchIndices := findAllMatches(startState, str, startState.lookaroundNumCaptureGroups)
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numMatchesFound := 0
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for _, matchIdx := range matchIndices {
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if s.assert == PLA || s.assert == NLA { // Lookahead - return true (or false) if at least one match starts at the current index
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if matchIdx[0].startIdx == idx {
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numMatchesFound++
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}
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}
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if s.assert == PLB || s.assert == NLB { // Lookbehind - return true (or false) if at least one match _ends_ at the current index.
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if matchIdx[0].endIdx == idx {
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numMatchesFound++
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}
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}
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}
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if s.assert == PLA || s.assert == PLB { // Positive assertions want at least one match
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return numMatchesFound > 0
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}
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if s.assert == NLA || s.assert == NLB { // Negative assertions only want zero matches
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return numMatchesFound == 0
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}
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}
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return true
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}
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// Returns true if the contents of 's' contain the value at the given index of the given string
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func (s State) contentContains(str []rune, idx int) bool {
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if s.assert != NONE {
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return s.checkAssertion(str, idx)
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}
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if s.allChars {
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return !slices.Contains(slices.Concat(notDotChars, s.except), str[idx]) // Return true only if the index isn't a 'notDotChar', or isn't one of the exception characters for the current node.
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}
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// Default - s.assert must be NONE
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return slices.Contains(s.content, int(str[idx]))
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}
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func (s State) isLookaround() bool {
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return s.assert == PLA || s.assert == PLB || s.assert == NLA || s.assert == NLB
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}
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// Returns the matches for the character at the given index of the given string.
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// Also returns the number of matches. Returns -1 if an assertion failed.
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func (s State) matchesFor(str []rune, idx int) ([]*State, int) {
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// Assertions can be viewed as 'checks'. If the check fails, we return
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// an empty array and 0.
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// If it passes, we treat it like any other state, and return all the transitions.
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if s.assert != NONE {
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if s.checkAssertion(str, idx) == false {
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return make([]*State, 0), -1
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}
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}
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listTransitions := s.transitions[int(str[idx])]
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for _, dest := range s.transitions[int(ANY_CHAR)] {
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if !slices.Contains(slices.Concat(notDotChars, dest.except), str[idx]) {
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// Add an allChar state to the list of matches if:
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// a. The current character isn't a 'notDotChars' character. In single line mode, this includes newline. In multiline mode, it doesn't.
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// b. The current character isn't the state's exception list.
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listTransitions = append(listTransitions, dest)
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}
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}
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numTransitions := len(listTransitions)
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return listTransitions, numTransitions
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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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if len(state.transitions) == 1 { // Eg. a*
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var moreThanOneTrans bool // Dummy variable, check if all the transitions for the current's state's contents have a length of one
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for _, c := range state.content {
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if len(state.transitions[c]) != 1 || state.transitions[c][0] != state {
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moreThanOneTrans = true
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}
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}
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state.isLast = !moreThanOneTrans
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}
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if state.isKleene { // A State representing a Kleene Star has transitions going out, which loop back to it. If all those transitions point to the same (single) state, then it must be a last state
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transitionDests := make([]*State, 0)
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for _, v := range state.transitions {
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transitionDests = append(transitionDests, v...)
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}
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if allEqual(transitionDests...) {
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state.isLast = true
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return
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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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// Concatenates s1 and s2, returns the start of the concatenation.
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func concatenate(s1 *State, s2 *State) *State {
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if s1 == nil {
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return s2
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}
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for i := range s1.output {
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for _, c := range s2.content { // Create transitions for every element in s1's content to s2'
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s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], s2)
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}
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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 = newContents(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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for _, c := range toReturn.content {
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s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], toReturn)
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}
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}
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for _, c := range s1.content {
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toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], &s1)
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}
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return toReturn
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}
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func alternate(s1 *State, s2 *State) *State {
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toReturn := &State{}
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toReturn.transitions = make(map[int][]*State)
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toReturn.output = append(toReturn.output, s1.output...)
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toReturn.output = append(toReturn.output, s2.output...)
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// Unique append is used here (and elsewhere) to ensure that,
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// for any given transition, a state can only be mentioned once.
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// For example, given the transition 'a', the state 's1' can only be mentioned once.
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// This would lead to multiple instances of the same set of match indices, since both
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// 's1' states would be considered to match.
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for _, c := range s1.content {
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toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s1)
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}
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for _, c := range s2.content {
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toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s2)
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}
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toReturn.content = newContents(EPSILON)
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toReturn.isEmpty = true
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return toReturn
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}
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func question(s1 *State) *State { // Use the fact that ab? == a(b|)
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s2 := &State{}
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s2.transitions = make(map[int][]*State)
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s2.content = newContents(EPSILON)
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s2.output = append(s2.output, s2)
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s2.isEmpty = true
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s3 := alternate(s1, s2)
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return s3
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}
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