Added lookaround-related fields to State struct, added lookaround support to checkAssertion()

master
Aadhavan Srinivasan 1 month ago
parent 051a8551f3
commit 77d19cd84e

@ -1,6 +1,8 @@
package main
import "slices"
import (
"slices"
)
const EPSILON int = 0
@ -12,19 +14,24 @@ const (
EOS
WBOUND
NONWBOUND
PLA // Positive lookahead
NLA // Negative lookahead
PLB // Positive lookbehind
NLB // Negative lookbehind
)
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
zeroMatchFound bool // Whether or not the state has been used for a zero-length match - only relevant for zero states
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.
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
zeroMatchFound bool // Whether or not the state has been used for a zero-length match - only relevant for zero states
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
}
// Clones the NFA starting from the given state.
@ -43,16 +50,17 @@ func cloneStateHelper(state *State, cloneMap map[*State]*State) *State {
// 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...),
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,
}
cloneMap[state] = clone
for i, s := range state.output {
@ -90,6 +98,36 @@ func (s State) checkAssertion(str []rune, idx int) bool {
if s.assert == NONWBOUND {
return !isWordBoundary(str, idx)
}
if s.assert == PLA || s.assert == PLB || s.assert == NLA || s.assert == NLB { // Lookaround
// The process here is simple:
// 1. Compile the regex stored in the state's contents.
// 2. Run it on the test string.
// 3. Based on the kind of lookaround (and the indices we get), determine what action to take.
regex := s.lookaroundRegex
re_postfix := shuntingYard(regex)
startState := thompson(re_postfix)
matchIndices := findAllMatches(startState, str)
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 the current index
if matchIdx.startIdx == idx {
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.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
}

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