Renamed package 'greg' to 'regex'
This commit is contained in:
348
regex/nfa.go
Normal file
348
regex/nfa.go
Normal file
@@ -0,0 +1,348 @@
|
||||
package regex
|
||||
|
||||
import (
|
||||
"fmt"
|
||||
"slices"
|
||||
)
|
||||
|
||||
const EPSILON int = 0xF0000
|
||||
|
||||
type assertType int
|
||||
|
||||
const (
|
||||
NONE assertType = iota
|
||||
SOS
|
||||
EOS
|
||||
WBOUND
|
||||
NONWBOUND
|
||||
PLA // Positive lookahead
|
||||
NLA // Negative lookahead
|
||||
PLB // Positive lookbehind
|
||||
NLB // Negative lookbehind
|
||||
ALWAYS_TRUE // An assertion that is always true
|
||||
)
|
||||
|
||||
type State struct {
|
||||
content stateContents // Contents of current state
|
||||
isEmpty bool // If it is empty - Union operator and Kleene star 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 (maps a character (int representation) to a _list of states. This is useful if one character can lead multiple states eg. ab|aa)
|
||||
isKleene bool // Identifies whether current node is a 0-state representing Kleene star
|
||||
assert assertType // Type of assertion of current node - NONE means that the node doesn't assert anything
|
||||
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
|
||||
except []rune // Only valid if allChars is true - match all characters _except_ the ones in this block. Useful for inverting character classes.
|
||||
lookaroundRegex string // Only for lookaround states - Contents of the regex that the lookaround state holds
|
||||
lookaroundNFA *State // Holds the NFA of the lookaroundRegex - if it exists
|
||||
lookaroundNumCaptureGroups int // Number of capturing groups in lookaround regex if current node is a lookaround
|
||||
groupBegin bool // Whether or not the node starts a capturing group
|
||||
groupEnd bool // Whether or not the node ends a capturing group
|
||||
groupNum int // Which capturing group the node starts / ends
|
||||
// The following properties depend on the current match - I should think about resetting them for every match.
|
||||
zeroMatchFound bool // Whether or not the state has been used for a zero-length match - only relevant for zero states
|
||||
threadGroups []Group // Assuming that a state is part of a 'thread' in the matching process, this array stores the indices of capturing groups in the current thread. As matches are found for this state, its groups will be copied over.
|
||||
}
|
||||
|
||||
// Clones the NFA starting from the given state.
|
||||
func cloneState(start *State) *State {
|
||||
return cloneStateHelper(start, make(map[*State]*State))
|
||||
}
|
||||
|
||||
// Helper function for clone. The map is used to keep track of which states have
|
||||
// already been copied, and which ones haven't.
|
||||
// This function was created using output from Llama3.1:405B.
|
||||
func cloneStateHelper(state *State, cloneMap map[*State]*State) *State {
|
||||
// Base case - if the clone exists in our map, return it.
|
||||
if clone, exists := cloneMap[state]; exists {
|
||||
return clone
|
||||
}
|
||||
if state == nil {
|
||||
return nil
|
||||
}
|
||||
// Recursive case - if the clone doesn't exist, create it, add it to the map,
|
||||
// and recursively call for each of the transition states.
|
||||
clone := &State{
|
||||
content: append([]int{}, state.content...),
|
||||
isEmpty: state.isEmpty,
|
||||
isLast: state.isLast,
|
||||
output: make([]*State, len(state.output)),
|
||||
transitions: make(map[int][]*State),
|
||||
isKleene: state.isKleene,
|
||||
assert: state.assert,
|
||||
zeroMatchFound: state.zeroMatchFound,
|
||||
allChars: state.allChars,
|
||||
except: append([]rune{}, state.except...),
|
||||
lookaroundRegex: state.lookaroundRegex,
|
||||
groupEnd: state.groupEnd,
|
||||
groupBegin: state.groupBegin,
|
||||
groupNum: state.groupNum,
|
||||
}
|
||||
cloneMap[state] = clone
|
||||
for i, s := range state.output {
|
||||
if s == state {
|
||||
clone.output[i] = clone
|
||||
} else {
|
||||
clone.output[i] = cloneStateHelper(s, cloneMap)
|
||||
}
|
||||
}
|
||||
for k, v := range state.transitions {
|
||||
clone.transitions[k] = make([]*State, len(v))
|
||||
for i, s := range v {
|
||||
if s == state {
|
||||
clone.transitions[k][i] = clone
|
||||
} else {
|
||||
clone.transitions[k][i] = cloneStateHelper(s, cloneMap)
|
||||
}
|
||||
}
|
||||
}
|
||||
if state.lookaroundNFA == state {
|
||||
clone.lookaroundNFA = clone
|
||||
}
|
||||
clone.lookaroundNFA = cloneStateHelper(state.lookaroundNFA, cloneMap)
|
||||
return clone
|
||||
}
|
||||
|
||||
// Checks if the given state's assertion is true. Returns true if the given
|
||||
// state doesn't have an assertion.
|
||||
func (s State) checkAssertion(str []rune, idx int) bool {
|
||||
if s.assert == ALWAYS_TRUE {
|
||||
return true
|
||||
}
|
||||
if s.assert == SOS {
|
||||
// Single-line mode: Beginning of string
|
||||
// Multi-line mode: Previous character was newline
|
||||
return idx == 0 || (multilineMode && (idx > 0 && str[idx-1] == '\n'))
|
||||
}
|
||||
if s.assert == EOS {
|
||||
// Single-line mode: End of string
|
||||
// Multi-line mode: current character is newline
|
||||
// Index is at the end of the string, or it points to the last character which is a newline
|
||||
return idx == len(str) || (multilineMode && str[idx] == '\n')
|
||||
}
|
||||
if s.assert == WBOUND {
|
||||
return isWordBoundary(str, idx)
|
||||
}
|
||||
if s.assert == NONWBOUND {
|
||||
return !isWordBoundary(str, idx)
|
||||
}
|
||||
if s.isLookaround() {
|
||||
// The process here is simple:
|
||||
// 1. Compile the regex stored in the state's contents.
|
||||
// 2. Run it on a subset of the test string, that ends after the current index in the string
|
||||
// 3. Based on the kind of lookaround (and the indices we get), determine what action to take.
|
||||
startState := s.lookaroundNFA
|
||||
var runesToMatch []rune
|
||||
var strToMatch string
|
||||
if s.assert == PLA || s.assert == NLA {
|
||||
runesToMatch = str[idx:]
|
||||
} else {
|
||||
runesToMatch = str[:idx]
|
||||
}
|
||||
|
||||
if len(runesToMatch) == 0 {
|
||||
strToMatch = ""
|
||||
} else {
|
||||
strToMatch = string(runesToMatch)
|
||||
}
|
||||
|
||||
matchIndices := FindAllMatches(Reg{startState, s.lookaroundNumCaptureGroups}, strToMatch)
|
||||
|
||||
numMatchesFound := 0
|
||||
for _, matchIdx := range matchIndices {
|
||||
if s.assert == PLA || s.assert == NLA { // Lookahead - return true (or false) if at least one match starts at 0. Zero is used because the test-string _starts_ from idx.
|
||||
if matchIdx[0].StartIdx == 0 {
|
||||
numMatchesFound++
|
||||
}
|
||||
}
|
||||
if s.assert == PLB || s.assert == NLB { // Lookbehind - return true (or false) if at least one match _ends_ at the current index.
|
||||
if matchIdx[0].EndIdx == idx {
|
||||
numMatchesFound++
|
||||
}
|
||||
}
|
||||
}
|
||||
if s.assert == PLA || s.assert == PLB { // Positive assertions want at least one match
|
||||
return numMatchesFound > 0
|
||||
}
|
||||
if s.assert == NLA || s.assert == NLB { // Negative assertions only want zero matches
|
||||
return numMatchesFound == 0
|
||||
}
|
||||
}
|
||||
return true
|
||||
}
|
||||
|
||||
// Returns true if the contents of 's' contain the value at the given index of the given string
|
||||
func (s State) contentContains(str []rune, idx int) bool {
|
||||
if s.assert != NONE {
|
||||
return s.checkAssertion(str, idx)
|
||||
}
|
||||
if s.allChars {
|
||||
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.
|
||||
}
|
||||
// Default - s.assert must be NONE
|
||||
return slices.Contains(s.content, int(str[idx]))
|
||||
}
|
||||
|
||||
func (s State) isLookaround() bool {
|
||||
return s.assert == PLA || s.assert == PLB || s.assert == NLA || s.assert == NLB
|
||||
}
|
||||
|
||||
// Returns the matches for the character at the given index of the given string.
|
||||
// Also returns the number of matches. Returns -1 if an assertion failed.
|
||||
func (s State) matchesFor(str []rune, idx int) ([]*State, int) {
|
||||
// Assertions can be viewed as 'checks'. If the check fails, we return
|
||||
// an empty array and 0.
|
||||
// If it passes, we treat it like any other state, and return all the transitions.
|
||||
if s.assert != NONE {
|
||||
if s.checkAssertion(str, idx) == false {
|
||||
return make([]*State, 0), -1
|
||||
}
|
||||
}
|
||||
listTransitions := s.transitions[int(str[idx])]
|
||||
for _, dest := range s.transitions[int(ANY_CHAR)] {
|
||||
if !slices.Contains(slices.Concat(notDotChars, dest.except), str[idx]) {
|
||||
// Add an allChar state to the list of matches if:
|
||||
// a. The current character isn't a 'notDotChars' character. In single line mode, this includes newline. In multiline mode, it doesn't.
|
||||
// b. The current character isn't the state's exception list.
|
||||
listTransitions = append(listTransitions, dest)
|
||||
}
|
||||
}
|
||||
numTransitions := len(listTransitions)
|
||||
return listTransitions, numTransitions
|
||||
}
|
||||
|
||||
// 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 len(state.transitions) == 1 && len(state.transitions[state.content]) == 1 && state.transitions[state.content][0] == state { // Eg. a*
|
||||
if len(state.transitions) == 1 { // Eg. a*
|
||||
var moreThanOneTrans bool // Dummy variable, check if all the transitions for the current's state's contents have a length of one
|
||||
for _, c := range state.content {
|
||||
if len(state.transitions[c]) != 1 || state.transitions[c][0] != state {
|
||||
moreThanOneTrans = true
|
||||
}
|
||||
}
|
||||
state.isLast = !moreThanOneTrans
|
||||
}
|
||||
|
||||
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
|
||||
transitionDests := make([]*State, 0)
|
||||
for _, v := range state.transitions {
|
||||
transitionDests = append(transitionDests, v...)
|
||||
}
|
||||
if allEqual(transitionDests...) {
|
||||
state.isLast = true
|
||||
return
|
||||
}
|
||||
}
|
||||
if visited[state] == true {
|
||||
return
|
||||
}
|
||||
visited[state] = true
|
||||
for _, states := range state.transitions {
|
||||
for i := range states {
|
||||
if states[i] != state {
|
||||
verifyLastStatesHelper(states[i], visited)
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
// verifyLastStates enables the 'isLast' flag for the leaf nodes (last states)
|
||||
func verifyLastStates(start []*State) {
|
||||
verifyLastStatesHelper(start[0], make(map[*State]bool))
|
||||
}
|
||||
|
||||
// Concatenates s1 and s2, returns the start of the concatenation.
|
||||
func concatenate(s1 *State, s2 *State) *State {
|
||||
if s1 == nil {
|
||||
return s2
|
||||
}
|
||||
for i := range s1.output {
|
||||
for _, c := range s2.content { // Create transitions for every element in s1's content to s2'
|
||||
s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], s2)
|
||||
}
|
||||
}
|
||||
s1.output = s2.output
|
||||
return s1
|
||||
}
|
||||
|
||||
func kleene(s1 State) (*State, error) {
|
||||
if s1.isEmpty && s1.assert != NONE {
|
||||
return nil, fmt.Errorf("previous token is not quantifiable")
|
||||
}
|
||||
|
||||
toReturn := &State{}
|
||||
toReturn.transitions = make(map[int][]*State)
|
||||
toReturn.content = newContents(EPSILON)
|
||||
toReturn.isEmpty = true
|
||||
toReturn.isKleene = true
|
||||
toReturn.output = append(toReturn.output, toReturn)
|
||||
for i := range s1.output {
|
||||
for _, c := range toReturn.content {
|
||||
s1.output[i].transitions[c], _ = unique_append(s1.output[i].transitions[c], toReturn)
|
||||
}
|
||||
}
|
||||
for _, c := range s1.content {
|
||||
toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], &s1)
|
||||
}
|
||||
return toReturn, nil
|
||||
}
|
||||
|
||||
func alternate(s1 *State, s2 *State) *State {
|
||||
toReturn := &State{}
|
||||
toReturn.transitions = make(map[int][]*State)
|
||||
toReturn.output = append(toReturn.output, s1.output...)
|
||||
toReturn.output = append(toReturn.output, s2.output...)
|
||||
// Unique append is used here (and elsewhere) to ensure that,
|
||||
// for any given transition, a state can only be mentioned once.
|
||||
// For example, given the transition 'a', the state 's1' can only be mentioned once.
|
||||
// This would lead to multiple instances of the same set of match indices, since both
|
||||
// 's1' states would be considered to match.
|
||||
for _, c := range s1.content {
|
||||
toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s1)
|
||||
}
|
||||
for _, c := range s2.content {
|
||||
toReturn.transitions[c], _ = unique_append(toReturn.transitions[c], s2)
|
||||
}
|
||||
toReturn.content = newContents(EPSILON)
|
||||
toReturn.isEmpty = true
|
||||
|
||||
return toReturn
|
||||
}
|
||||
|
||||
func question(s1 *State) *State { // Use the fact that ab? == a(b|)
|
||||
s2 := &State{}
|
||||
s2.transitions = make(map[int][]*State)
|
||||
s2.content = newContents(EPSILON)
|
||||
s2.output = append(s2.output, s2)
|
||||
s2.isEmpty = true
|
||||
s3 := alternate(s1, s2)
|
||||
return s3
|
||||
}
|
||||
|
||||
// Creates and returns a new state with the 'default' values.
|
||||
func newState() State {
|
||||
ret := State{
|
||||
output: make([]*State, 0),
|
||||
transitions: make(map[int][]*State),
|
||||
assert: NONE,
|
||||
except: append([]rune{}, 0),
|
||||
lookaroundRegex: "",
|
||||
groupEnd: false,
|
||||
groupBegin: false,
|
||||
}
|
||||
ret.output = append(ret.output, &ret)
|
||||
return ret
|
||||
}
|
||||
|
||||
// Creates and returns a state that _always_ has a zero-length match.
|
||||
func zeroLengthMatchState() State {
|
||||
start := newState()
|
||||
start.content = newContents(EPSILON)
|
||||
start.isEmpty = true
|
||||
start.assert = ALWAYS_TRUE
|
||||
return start
|
||||
}
|
||||
Reference in New Issue
Block a user