Added lookaround-related fields to State struct, added lookaround support to checkAssertion()
This commit is contained in:
40
nfa.go
40
nfa.go
@@ -1,6 +1,8 @@
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package main
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import "slices"
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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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@@ -12,6 +14,10 @@ const (
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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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@@ -25,6 +31,7 @@ type State struct {
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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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}
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// Clones the NFA starting from the given state.
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@@ -53,6 +60,7 @@ func cloneStateHelper(state *State, cloneMap map[*State]*State) *State {
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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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}
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cloneMap[state] = clone
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for i, s := range state.output {
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@@ -90,6 +98,36 @@ func (s State) checkAssertion(str []rune, idx int) bool {
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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.assert == PLA || s.assert == PLB || s.assert == NLA || s.assert == NLB { // Lookaround
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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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regex := s.lookaroundRegex
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re_postfix := shuntingYard(regex)
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startState := thompson(re_postfix)
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matchIndices := findAllMatches(startState, str)
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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.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.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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