Trying to emulate backtracking by using string pointers within threads (something similar to rsc's 2nd regexp article)

regex/matching.go

@@ -1,6 +1,7 @@
 package regex
 
 import (
+	"container/heap"
 	"fmt"
 	"slices"
 	"sort"
@@ -271,7 +272,8 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 	foundPath := false
 	startIdx := offset
 	endIdx := offset
-	currentStates := make([]*nfaState, 0)
+	currentStates := &priorityQueue{}
+	heap.Init(currentStates)
 	tempStates := make([]*nfaState, 0) // Used to store states that should be used in next loop iteration
 	i := offset                        // Index in string
 	startingFrom := i                  // Store starting index
@@ -301,16 +303,19 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 		//		tempIndices[start.groupNum].startIdx = i
 	}
 
-	currentStates = append(currentStates, start)
-
+	start.threadSP = i
+	heap.Push(currentStates, newPriorQueueItem(start))
 	// Main loop
-	for i < len(str) {
+	for currentStates.Len() > 0 {
+		currentState := heap.Pop(currentStates)
 		foundPath = false
 
 		zeroStates := make([]*nfaState, 0)
 		// Keep taking zero-states, until there are no more left to take
 		// Objective: If any of our current states have transitions to 0-states, replace them with the 0-state. Do this until there are no more transitions to 0-states, or there are no more unique 0-states to take.
-		zeroStates, isZero := takeZeroState(currentStates, numGroups, i)
+		topStateItem := currentStates.peek()
+		topState := topStateItem.(*priorQueueItem).state
+		zeroStates, isZero := takeZeroState([]*nfaState{topState}, numGroups, i)
 		tempStates = append(tempStates, zeroStates...)
 		num_appended := 0
 		for isZero == true {
@@ -320,8 +325,13 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 				break
 			}
 		}
+		if isZero == true {
+			currentStates.Pop()
+		}
 
-		currentStates = slices.Concat(currentStates, tempStates)
+		for _, state := range tempStates {
+			heap.Push(currentStates, newPriorQueueItem(state))
+		}
 		tempStates = nil
 
 		// Take any transitions corresponding to current character
@@ -331,10 +341,11 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 		var lastStatePtr *nfaState = nil // Pointer to the last-state, if it was found
 		lastLookaroundInList := false    // Whether or not a last state (that is a lookaround) was in our list of states
 		for numStatesMatched == 0 && lastStateInList == false {
-			if len(currentStates) == 0 {
+			if currentStates.Len() == 0 {
 				break
 			}
-			state, _ := pop(&currentStates)
+			stateItem := heap.Pop(currentStates)
+			state := stateItem.(*priorQueueItem).state
 			matches, numMatches := state.matchesFor(str, i)
 			if numMatches > 0 {
 				numStatesMatched++
@@ -344,6 +355,7 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 					if m.threadGroups == nil {
 						m.threadGroups = newMatch(numGroups + 1)
 					}
+					m.threadSP = state.threadSP + 1
 					copy(m.threadGroups, state.threadGroups)
 				}
 			}
@@ -382,7 +394,8 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 		// 	a. A last-state
 		// 	b. Empty
 		// 	c. Doesn't assert anything
-		for _, s := range currentStates {
+		for _, stateItem := range *currentStates {
+			s := stateItem.state
 			if s.isLast && s.isEmpty && s.assert == noneAssert {
 				lastStatePtr = s
 				lastStateInList = true
@@ -403,7 +416,10 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 
 		// Check if we can find a zero-length match
 		if foundPath == false {
-			if ok := zeroMatchPossible(str, i, numGroups, currentStates...); ok {
+			currentStatesList := funcMap(*currentStates, func(item *priorQueueItem) *nfaState {
+				return item.state
+			})
+			if ok := zeroMatchPossible(str, i, numGroups, currentStatesList...); ok {
 				if tempIndices[0].IsValid() == false {
 					tempIndices[0] = Group{startIdx, startIdx}
 				}
@@ -423,8 +439,11 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 			}
 			return false, []Group{}, startIdx
 		}
-		currentStates = make([]*nfaState, len(tempStates))
-		copy(currentStates, tempStates)
+		currentStates = &priorityQueue{}
+		slices.Reverse(tempStates)
+		for _, state := range tempStates {
+			heap.Push(currentStates, newPriorQueueItem(state))
+		}
 		tempStates = nil
 
 		i++
@@ -432,7 +451,10 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 
 	// End-of-string reached. Go to any 0-states, until there are no more 0-states to go to. Then check if any of our states are in the end position.
 	// This is the exact same algorithm used inside the loop, so I should probably put it in a function.
-	zeroStates, isZero := takeZeroState(currentStates, numGroups, i)
+	if currentStates.Len() > 0 {
+		topStateItem := currentStates.peek()
+		topState := topStateItem.(*priorQueueItem).state
+		zeroStates, isZero := takeZeroState([]*nfaState{topState}, numGroups, i)
 		tempStates = append(tempStates, zeroStates...)
 		num_appended := 0 // Number of unique states addded to tempStates
 		for isZero == true {
@@ -442,11 +464,15 @@ func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups in
 				break
 			}
 		}
+	}
 
-	currentStates = append(currentStates, tempStates...)
+	for _, state := range tempStates {
+		heap.Push(currentStates, newPriorQueueItem(state))
+	}
 	tempStates = nil
 
-	for _, state := range currentStates {
+	for _, stateItem := range *currentStates {
+		state := stateItem.state
 		// Only add the match if the start index is in bounds. If the state has an assertion,
 		// make sure the assertion checks out.
 		if state.isLast && i <= len(str) {