Added function and examples for ReplaceAllFunc()

Reviewed-on: #2

Makefile

@@ -6,8 +6,8 @@ fmt:
 vet: fmt
 	go vet ./...
 buildLib: vet
-	go build -gcflags="-N -l" ./...
+	go build -gcflags="all=-N -l" ./...
 buildCmd: buildLib
-	go build -C cmd/ -o re ./...
+	go build -C cmd/ -gcflags="all=-N -l" -o re ./...
 test: buildCmd
 	go test -v ./...

cmd/main.go

@@ -121,12 +121,12 @@ func main() {
 		}
 		matchIndices := make([]reg.Match, 0)
 		if matchNumFlagEnabled {
-			tmp, err := reg.FindNthMatch(regComp, test_str, *matchNum)
+			tmp, err := regComp.FindNthMatch(test_str, *matchNum)
 			if err == nil {
 				matchIndices = append(matchIndices, tmp)
 			}
 		} else {
-			matchIndices = reg.FindAllMatches(regComp, test_str)
+			matchIndices = regComp.FindAllSubmatch(test_str)
 		}
 
 		if *printMatchesFlag {
@@ -137,7 +137,7 @@ func main() {
 					fmt.Fprintf(out, "Line %d:\n", lineNum)
 				}
 				for _, m := range matchIndices {
-					fmt.Fprintf(out, "%s\n", m.ToString())
+					fmt.Fprintf(out, "%s\n", m.String())
 				}
 				err := out.Flush()
 				if err != nil {

cmd/unique_array.go

@@ -16,7 +16,6 @@ func (s *uniq_arr[T]) add(vals ...T) {
 			s.backingMap[item] = struct{}{}
 		}
 	}
-	return
 }
 
 func (s uniq_arr[T]) contains(val T) bool {

regex/compile.go

@@ -12,10 +12,43 @@ var notDotChars []rune
 
 // A Reg represents the result of compiling a regular expression. It contains
 // the startState of the NFA representation of the regex, and the number of capturing
-// groups in the regex.
+// groups in the regex. It also contains the expression string.
 type Reg struct {
-	start     *nfaState
-	numGroups int
+	start         *nfaState
+	numGroups     int
+	str           string
+	preferLongest bool
+}
+
+// NumSubexp returns the number of sub-expressions in the given [Reg]. This is equivalent
+// to the number of capturing groups.
+func (re Reg) NumSubexp() int {
+	return re.numGroups
+}
+
+// String returns the string used to compile the expression.
+func (re Reg) String() string {
+	return re.str
+}
+
+// MarshalText implements [encoding.TextMarshaler]. The output is equivalent to that of [Reg.String].
+// Any flags passed as arguments (including calling [Reg.Longest]) are lost.
+func (re *Reg) MarshalText() ([]byte, error) {
+	return []byte(re.String()), nil
+}
+
+// UnmarshalText implements [encoding.TextUnmarshaler]. It calls [Reg.Compile] on the given byte-slice. If it returns successfully,
+// then the result of the compilation is stored in re. The result of [Reg.Compile] is returned.
+func (re *Reg) UnmarshalText(text []byte) error {
+	newReg, err := Compile(string(text))
+	if err == nil {
+		*re = newReg
+	}
+	return err
+}
+
+func (re *Reg) Longest() {
+	re.preferLongest = true
 }
 
 const concatRune rune = 0xF0001
@@ -810,13 +843,12 @@ func thompson(re []postfixNode) (Reg, error) {
 	// In these cases, we will return an NFA with 1 state, with an assertion that is always true.
 	if len(re) == 0 {
 		start := zeroLengthMatchState()
-		nfa = append(nfa, &start)
+		nfa = append(nfa, start)
 	}
 
 	for _, c := range re {
 		if c.nodetype == characterNode || c.nodetype == assertionNode {
 			stateToAdd := nfaState{}
-			stateToAdd.transitions = make(map[int][]*nfaState)
 			if c.allChars {
 				stateToAdd.allChars = true
 				if len(c.except) != 0 {
@@ -928,7 +960,6 @@ func thompson(re []postfixNode) (Reg, error) {
 			s.isEmpty = true
 			s.output = make([]*nfaState, 0)
 			s.output = append(s.output, s)
-			s.transitions = make(map[int][]*nfaState)
 			// LPAREN nodes are just added normally
 			if c.nodetype == lparenNode {
 				numGroups++
@@ -943,7 +974,9 @@ func thompson(re []postfixNode) (Reg, error) {
 			// and added back in.
 			// If the middle node doesn't exist (ie. something like '()' ), that's fine, I just connect the LPAREN
 			// and RPAREN nodes.
-			// If neither node exists, that's a problem so I return an error.
+			// If the middle node exists but is itself the start of a group, then that _must_ be the opening paren for
+			// the closing paren that I'm on. I put the third node back (because it isn't involved in the capturing group), then
+			// I concatenate those two and add them. If neither node exists, that's a problem so I return an error.
 			if c.nodetype == rparenNode {
 				s.groupEnd = true
 				middleNode, err1 := pop(&nfa)
@@ -958,6 +991,11 @@ func thompson(re []postfixNode) (Reg, error) {
 					s.groupNum = lparenNode.groupNum
 					to_add := concatenate(lparenNode, s)
 					nfa = append(nfa, to_add)
+				} else if middleNode.groupBegin && middleNode.numTransitions() == 0 { // The middle node is a lone lparen - something like '(())', and I'm looking at the first rparen
+					nfa = append(nfa, lparenNode)    // I shouldn't have popped this out, because it is not involved in the current capturing group
+					s.groupNum = middleNode.groupNum // In this case, the 'middle' node is actually an lparen
+					to_add := concatenate(middleNode, s)
+					nfa = append(nfa, to_add)
 				} else {
 					// At this point, we assume all three nodes are valid ('lparenNode', 'middleNode' and 's')
 					if lparenNode.groupBegin {
@@ -976,7 +1014,8 @@ func thompson(re []postfixNode) (Reg, error) {
 		if c.nodetype == charclassNode { // A Character class consists of all the nodes in it, alternated
 			// Map the list of nodes to a list of states, each state containing the contents of a specific node
 			states := funcMap(c.nodeContents, func(node postfixNode) *nfaState {
-				s := newState()
+				s := &nfaState{}
+				s.output = append(s.output, s)
 				nodeContents := node.contents
 				if caseInsensitive {
 					nodeContents = slices.Concat(funcMap(nodeContents, func(r rune) []rune {
@@ -990,7 +1029,7 @@ func thompson(re []postfixNode) (Reg, error) {
 						return n.contents
 					})...)
 				}
-				return &s
+				return s
 			})
 			// Reduce the list of states down to a single state by alternating them
 			toAdd := funcReduce(states, func(s1 *nfaState, s2 *nfaState) *nfaState {
@@ -1017,14 +1056,14 @@ func thompson(re []postfixNode) (Reg, error) {
 			if err != nil {
 				return Reg{}, fmt.Errorf("error applying kleene star")
 			}
-			stateToAdd, err := kleene(*s1)
+			stateToAdd, err := kleene(s1)
 			if err != nil {
 				return Reg{}, err
 			}
 			nfa = append(nfa, stateToAdd)
 		case plusNode: // a+ is equivalent to aa*
 			s1 := mustPop(&nfa)
-			s2, err := kleene(*s1)
+			s2, err := kleene(s1)
 			if err != nil {
 				return Reg{}, err
 			}
@@ -1035,7 +1074,10 @@ func thompson(re []postfixNode) (Reg, error) {
 			if err != nil {
 				return Reg{}, fmt.Errorf("error applying question operator")
 			}
-			s2 := question(s1)
+			s2, err := question(s1)
+			if err != nil {
+				return Reg{}, err
+			}
 			nfa = append(nfa, s2)
 		case pipeNode:
 			// A pipe operator doesn't actually need either operand to be present. If an operand isn't present,
@@ -1046,21 +1088,21 @@ func thompson(re []postfixNode) (Reg, error) {
 			// 	'|a'
 			// 	'^a|'
 			// 	'^|a'
-			s1, err1 := pop(&nfa)
-			s2, err2 := pop(&nfa)
-			if err2 != nil || (s2.groupBegin && len(s2.transitions) == 0) { // Doesn't exist, or its just an LPAREN
+			s2, err1 := pop(&nfa)
+			s1, err2 := pop(&nfa)
+			if err2 != nil || (s2.groupBegin && s2.numTransitions() == 0) { // Doesn't exist, or its just an LPAREN
 				if err2 == nil { // Roundabout way of saying that this node existed, but it was an LPAREN, so we append it back
 					nfa = append(nfa, s2)
 				}
 				tmp := zeroLengthMatchState()
-				s2 = &tmp
+				s2 = tmp
 			}
-			if err1 != nil || (s1.groupBegin && len(s1.transitions) == 0) { // Doesn't exist, or its just an LPAREN
+			if err1 != nil || (s1.groupBegin && s1.numTransitions() == 0) { // Doesn't exist, or its just an LPAREN
 				if err1 == nil { // See above for explanation
 					nfa = append(nfa, s1)
 				}
 				tmp := zeroLengthMatchState()
-				s1 = &tmp
+				s1 = tmp
 			}
 			s3 := alternate(s1, s2)
 			nfa = append(nfa, s3)
@@ -1087,14 +1129,18 @@ func thompson(re []postfixNode) (Reg, error) {
 				stateToAdd = concatenate(stateToAdd, cloneState(poppedState))
 			}
 			if c.endReps == infinite_reps { // Case 3
-				s2, err := kleene(*poppedState)
+				s2, err := kleene(poppedState)
 				if err != nil {
 					return Reg{}, err
 				}
 				stateToAdd = concatenate(stateToAdd, s2)
 			} else { // Case 2
 				for i := c.startReps; i < c.endReps; i++ {
-					stateToAdd = concatenate(stateToAdd, question(cloneState(poppedState)))
+					tmp, err := question(cloneState(poppedState))
+					if err != nil {
+						return Reg{}, fmt.Errorf("error processing bounded repetition")
+					}
+					stateToAdd = concatenate(stateToAdd, tmp)
 				}
 			}
 			nfa = append(nfa, stateToAdd)
@@ -1104,16 +1150,21 @@ func thompson(re []postfixNode) (Reg, error) {
 		return Reg{}, fmt.Errorf("invalid regex")
 	}
 
-	verifyLastStates(nfa)
+	lastState := newState()
+	lastState.isLast = true
 
-	return Reg{nfa[0], numGroups}, nil
+	concatenate(nfa[0], &lastState)
+
+	// The string is empty here, because we add it in Compile()
+	return Reg{nfa[0], numGroups, "", false}, nil
 
 }
 
-// Compiles the given regular expression into a Reg type, suitable for use with the
-// matching functions. The second return value is non-nil if a compilation error has
-// occured. As such, the error value must be checked before using the Reg returned by this function.
-// The second parameter is an optional list of flags, passed to the parsing function shuntingYard.
+// Compile compiles the given regular expression into a [Reg].
+//
+// An error value != nil indicates that the regex was invalid; the error message should provide
+// detailed information on the nature of the error.
+// The second parameter is a sequence of zero or more [ReFlag] values, that modify the behavior of the regex.
 func Compile(re string, flags ...ReFlag) (Reg, error) {
 	nodes, err := shuntingYard(re, flags...)
 	if err != nil {
@@ -1123,5 +1174,15 @@ func Compile(re string, flags ...ReFlag) (Reg, error) {
 	if err != nil {
 		return Reg{}, fmt.Errorf("error compiling regex: %w", err)
 	}
+	reg.str = re
 	return reg, nil
 }
+
+// MustCompile panics if Compile returns an error. They are identical in all other respects.
+func MustCompile(re string, flags ...ReFlag) Reg {
+	reg, err := Compile(re, flags...)
+	if err != nil {
+		panic(err)
+	}
+	return reg
+}

regex/doc.go

@@ -4,6 +4,8 @@ Package regex implements regular expression search, using a custom non-bracktrac
 The engine relies completely on UTF-8 codepoints. As such, it is capable of matching characters
 from other languages, emojis and symbols.
 
+The API and regex syntax are largely compatible with that of the stdlib's [regexp], with a few key differences (see 'Key Differences with regexp').
+
 The full syntax is specified below.
 
 # Syntax
@@ -31,7 +33,7 @@ Perl classes:
 	\d				Match any digit character ([0-9])
 	\D				Match any non-digit character ([^0-9])
 	\w				Match any word character ([a-zA-Z0-9_])
-	\W				Match any word character ([^a-zA-Z0-9_])
+	\W				Match any non-word character ([^a-zA-Z0-9_])
 	\s				Match any whitespace character ([ \t\n])
 	\S				Match any non-whitespace character ([^ \t\n])
 
@@ -55,8 +57,8 @@ POSIX classes (inside normal character classes):
 Composition:
 
 	def				Match d, followed by e, followed by f
-	x|y				Match x or y (prefer longer one)
-	xy|z			Match xy or z
+	x|y				Match x or y (prefer x)
+	xy|z			Match xy or z (prefer xy)
 
 Repitition (always greedy, preferring more):
 
@@ -84,9 +86,77 @@ Assertions:
 	\b				Match at a word boundary (a word character followed by a non-word character, or vice-versa)
 	\B				Match at a non-word boundary (a word character followed by a word character, or vice-versa)
 
-# Flags
+Lookarounds:
 
-Flags are used to change the behavior of the engine. None of them are enabled by default. They are passed as an [ReFlag] slice to [Compile].
-The list of flags, and their purpose, is provided in the type definition.
+	x(?=y)			Positive lookahead - Match x if followed by y
+	x(?!y)			Negative lookahead - Match x if NOT followed by y
+	(?<=x)y			Positive lookbehind - Match y if preceded by x
+	(?<!x)y			Negative lookbehind - Match y if NOT preceded by x
+
+Numeric ranges:
+
+	<x-y>			Match any number from x to y (inclusive) (x and y must be positive numbers)
+	\<x				Match a literal '<' followed by x
+
+# Key Differences with regexp
+
+The engine and the API differ from [regexp] in a few ways, some of them very subtle.
+The key differences are mentioned below.
+
+1. Greediness:
+
+This engine currently does not support non-greedy operators.
+
+2. Byte-slices and runes:
+
+My engine does not support byte-slices. When a matching function receives a string, it converts it into a
+rune-slice to iterate through it. While this has some space overhead, the convenience of built-in unicode
+support made the tradeoff worth it.
+
+3. Return values
+
+Rather than using primitives for return values, my engine defines two types that are used as return
+values: a [Group] represents a capturing group, and a [Match] represents a list of groups.
+
+[regexp] specifies a regular expression that gives a list of all the matching functions that it supports. The
+equivalent expression for this engine is shown below. Note that 'Index' is the default.
+
+	Find(All)?(String)?(Submatch)?
+
+[Reg.Find] returns the index of the leftmost match in the string.
+
+If a function contains 'All' it returns all matches instead of just the leftmost one.
+
+If a function contains 'String' it returns the matched text, rather than the index in the string.
+
+If a function contains 'Submatch' it returns the match, including all submatches found by
+capturing groups.
+
+The term '0-group' is used to refer to the 0th capturing group of a match (which is the entire match).
+Given the following regex:
+
+	x(y)
+
+and the input string:
+
+	xyz
+
+The 0th group would contain 'xy' and the 1st group would contain 'y'. Any matching function without 'Submatch' in its name
+returns the 0-group.
+
+# Feature Differences
+
+The following features from [regexp] are (currently) NOT supported:
+ 1. Named capturing groups
+ 2. Non-greedy operators
+ 3. Unicode character classes
+ 4. Embedded flags (flags are instead passed as arguments to [Compile])
+ 5. Literal text with \Q ... \E
+
+The following features are not available in [regexp], but are supported in my engine:
+ 1. Lookarounds
+ 2. Numeric ranges
+
+I hope to shorten the first list, and expand the second.
 */
 package regex

regex/example_test.go

@@ -0,0 +1,181 @@
+package regex_test
+
+import (
+	"fmt"
+	"strings"
+
+	"gitea.twomorecents.org/Rockingcool/kleingrep/regex"
+)
+
+func ExampleReg_Find() {
+	regexStr := "b|a"
+	regexComp := regex.MustCompile(regexStr)
+
+	match, _ := regexComp.Find("banana")
+	fmt.Println(match.String())
+
+	// Output: 0	1
+}
+
+func ExampleReg_FindAll() {
+	regexStr := "b|a"
+	regexComp := regex.MustCompile(regexStr)
+
+	matches := regexComp.FindAll("banana")
+	for _, group := range matches {
+		fmt.Println(group.String())
+	}
+
+	// Output: 0	1
+	// 1	2
+	// 3	4
+	// 5	6
+}
+
+func ExampleReg_FindString() {
+	regexStr := `\w+\s+(?=sheep)`
+	regexComp := regex.MustCompile(regexStr)
+
+	matchStr := regexComp.FindString("pink cows and yellow sheep")
+	fmt.Println(matchStr)
+	// Output: yellow
+}
+
+func ExampleReg_FindSubmatch() {
+	regexStr := `(\d)\.(\d)(\d)`
+	regexComp := regex.MustCompile(regexStr)
+
+	match, _ := regexComp.FindSubmatch("3.14")
+	fmt.Println(match[0])
+	fmt.Println(match[1])
+	fmt.Println(match[2])
+	// Output: 0	4
+	// 0	1
+	// 2	3
+}
+
+func ExampleReg_FindStringSubmatch() {
+	regexStr := `(\d{4})-(\d{2})-(\d{2})`
+	regexComp := regex.MustCompile(regexStr)
+	inputStr := `The date is 2025-02-10`
+
+	match := regexComp.FindStringSubmatch(inputStr)
+	fmt.Println(match[1])
+	fmt.Println(match[3])
+	// Output: 2025
+	// 10
+}
+
+func ExampleReg_FindAllSubmatch() {
+	regexStr := `(\d)\.(\d)(\d)`
+	regexComp := regex.MustCompile(regexStr)
+
+	matches := regexComp.FindAllSubmatch("3.14+8.97")
+	fmt.Println(matches[0][0]) // 0-group (entire match) of 1st match (0-indexed)
+	fmt.Println(matches[0][1]) // 1st group of 1st match
+	fmt.Println(matches[1][0]) // 0-group of 2nd match
+	fmt.Println(matches[1][1]) // 1st group of 2nd math
+	// Output: 0	4
+	// 0	1
+	// 5	9
+	// 5	6
+}
+
+func ExampleReg_FindAllString() {
+	regexStr := `<0-255>\.<0-255>\.<0-255>\.<0-255>`
+	inputStr := `192.168.220.7 pings 9.9.9.9`
+	regexComp := regex.MustCompile(regexStr)
+
+	matchStrs := regexComp.FindAllString(inputStr)
+
+	fmt.Println(matchStrs[0])
+	fmt.Println(matchStrs[1])
+	// Output: 192.168.220.7
+	// 9.9.9.9
+}
+
+func ExampleReg_FindAllStringSubmatch() {
+	// 'https' ...
+	// followed by 1 or more alphanumeric characters (including period) ...
+	// then a forward slash ...
+	// followed by one more of :
+	// 		word character,
+	// 		question mark,
+	// 		period,
+	// 		equals sign
+	regexStr := `https://([a-z0-9\.]+)/([\w.?=]+)`
+	regexComp := regex.MustCompile(regexStr, regex.RE_CASE_INSENSITIVE)
+	inputStr := `You can find me at https://twomorecents.org/index.html and https://news.ycombinator.com/user?id=aadhavans`
+
+	matchIndices := regexComp.FindAllStringSubmatch(inputStr)
+	fmt.Println(matchIndices[0][1]) // 1st group of 1st match (0-indexed)
+	fmt.Println(matchIndices[0][2]) // 2nd group of 1st match
+	fmt.Println(matchIndices[1][1]) // 1st group of 2nd match
+	fmt.Println(matchIndices[1][2]) // 2nd group of 2nd match
+	// Output: twomorecents.org
+	// index.html
+	// news.ycombinator.com
+	// user?id=aadhavans
+
+}
+
+func ExampleReg_Expand() {
+	inputStr := `option1: value1
+	option2: value2`
+	regexStr := `(\w+): (\w+)`
+	templateStr := "$1 = $2\n"
+	regexComp := regex.MustCompile(regexStr, regex.RE_MULTILINE)
+	result := ""
+	for _, submatches := range regexComp.FindAllSubmatch(inputStr) {
+		result = regexComp.Expand(result, templateStr, inputStr, submatches)
+	}
+	fmt.Println(result)
+	// Output: option1 = value1
+	// option2 = value2
+
+}
+
+func ExampleReg_LiteralPrefix() {
+	regexStr := `a(b|c)d*`
+	regexComp := regex.MustCompile(regexStr)
+	prefix, complete := regexComp.LiteralPrefix()
+	fmt.Println(prefix)
+	fmt.Println(complete)
+	// Output: a
+	// false
+}
+
+func ExampleReg_Longest() {
+	regexStr := `x|xx`
+	inputStr := "xx"
+	regexComp := regex.MustCompile(regexStr)
+	fmt.Println(regexComp.FindString(inputStr))
+	regexComp.Longest()
+	fmt.Println(regexComp.FindString(inputStr))
+	// Output: x
+	// xx
+}
+
+func ExampleReg_ReplaceAll() {
+	regexStr := `(\d)(\w)`
+	inputStr := "5d9t"
+	regexComp := regex.MustCompile(regexStr)
+	fmt.Println(regexComp.ReplaceAll(inputStr, `$2$1`))
+	// Output: d5t9
+}
+
+func ExampleReg_ReplaceAllLiteral() {
+	regexStr := `fox|dog`
+	inputStr := "the quick brown fox jumped over the lazy dog"
+	regexComp := regex.MustCompile(regexStr)
+	fmt.Println(regexComp.ReplaceAllLiteral(inputStr, `duck`))
+	// Output: the quick brown duck jumped over the lazy duck
+}
+
+func ExampleReg_ReplaceAllFunc() {
+	regexStr := `\w{5,}`
+	inputStr := `all five or more letter words in this string are capitalized`
+	regexComp := regex.MustCompile(regexStr)
+	fmt.Println(regexComp.ReplaceAllFunc(inputStr, strings.ToUpper))
+	// Output: all five or more LETTER WORDS in this STRING are CAPITALIZED
+}

regex/matching.go

@@ -2,13 +2,20 @@ package regex
 
 import (
 	"fmt"
-	"sort"
+	"strconv"
+	"unicode"
 )
 
-// a Match stores a slice of all the capturing groups in a match.
+// A Match represents a match found by the regex in a given string.
+// It is represented as a list of groups, where the nth element contains
+// the contents of the nth capturing group. Note that the group may not be valid
+// (see [Group.IsValid]). The element at index 0 is known
+// as the 0-group, and represents the contents of the entire match.
+//
+// See [Reg.FindSubmatch] for an example.
 type Match []Group
 
-// a Group represents a group. It contains the start index and end index of the match
+// a Group represents a capturing group. It contains the start and index of the group.
 type Group struct {
 	StartIdx int
 	EndIdx   int
@@ -23,151 +30,153 @@ func newMatch(size int) Match {
 	return toRet
 }
 
-// Returns the number of valid groups in the match
-func (m Match) numValidGroups() int {
-	numValid := 0
-	for _, g := range m {
-		if g.StartIdx >= 0 && g.EndIdx >= 0 {
-			numValid++
-		}
-	}
-	return numValid
-}
-
 // Returns a string containing the indices of all (valid) groups in the match
-func (m Match) ToString() string {
+func (m Match) String() string {
 	var toRet string
 	for i, g := range m {
-		if g.isValid() {
+		if g.IsValid() {
 			toRet += fmt.Sprintf("Group %d\n", i)
-			toRet += g.toString()
+			toRet += g.String()
 			toRet += "\n"
 		}
 	}
 	return toRet
 }
 
-// Converts the Group into a string representation:
-func (idx Group) toString() string {
+// String converts the Group into a string representation.
+func (idx Group) String() string {
 	return fmt.Sprintf("%d\t%d", idx.StartIdx, idx.EndIdx)
 }
 
-// Returns whether a group contains valid indices
-func (g Group) isValid() bool {
+// IsValid returns whether a group is valid (ie. whether it matched any text). It
+// simply ensures that both indices of the group are >= 0.
+func (g Group) IsValid() bool {
 	return g.StartIdx >= 0 && g.EndIdx >= 0
 }
 
-// takeZeroState takes the 0-state (if such a transition exists) for all states in the
-// given slice. It returns the resulting states. If any of the resulting states is a 0-state,
-// the second ret val is true.
-// If a state begins or ends a capturing group, its 'thread' is updated to contain the correct index.
-func takeZeroState(states []*nfaState, numGroups int, idx int) (rtv []*nfaState, isZero bool) {
-	for _, state := range states {
-		if len(state.transitions[epsilon]) > 0 {
-			for _, s := range state.transitions[epsilon] {
-				if s.threadGroups == nil {
-					s.threadGroups = newMatch(numGroups + 1)
-				}
-				copy(s.threadGroups, state.threadGroups)
-				if s.groupBegin {
-					s.threadGroups[s.groupNum].StartIdx = idx
-					//					openParenGroups = append(openParenGroups, s.groupNum)
-				}
-				if s.groupEnd {
-					s.threadGroups[s.groupNum].EndIdx = idx
-					//					closeParenGroups = append(closeParenGroups, s.groupNum)
-				}
-			}
-			rtv = append(rtv, state.transitions[epsilon]...)
-		}
-	}
-	for _, state := range rtv {
-		if len(state.transitions[epsilon]) > 0 {
-			return rtv, true
-		}
-	}
-	return rtv, false
+// Simple function, makes it easier to map this over a list of matches
+func getZeroGroup(m Match) Group {
+	return m[0]
 }
 
-// zeroMatchPossible returns true if a zero-length match is possible
-// from any of the given states, given the string and our position in it.
-// It uses the same algorithm to find zero-states as the one inside the loop,
-// so I should probably put it in a function.
-func zeroMatchPossible(str []rune, idx int, numGroups int, states ...*nfaState) bool {
-	zeroStates, isZero := takeZeroState(states, numGroups, idx)
-	tempstates := make([]*nfaState, 0, len(zeroStates)+len(states))
-	tempstates = append(tempstates, states...)
-	tempstates = append(tempstates, zeroStates...)
-	num_appended := 0 // number of unique states addded to tempstates
-	for isZero == true {
-		zeroStates, isZero = takeZeroState(tempstates, numGroups, idx)
-		tempstates, num_appended = unique_append(tempstates, zeroStates...)
-		if num_appended == 0 { // break if we haven't appended any more unique values
-			break
-		}
-	}
-	for _, state := range tempstates {
-		if state.isEmpty && (state.assert == noneAssert || state.checkAssertion(str, idx)) && state.isLast {
-			return true
-		}
-	}
-	return false
+func copyThread(to *nfaState, from nfaState) {
+	to.threadGroups = append([]Group{}, from.threadGroups...)
 }
 
-// Prunes the slice by removing overlapping indices.
-func pruneIndices(indices []Match) []Match {
-	// First, sort the slice by the start indices
-	sort.Slice(indices, func(i, j int) bool {
-		return indices[i][0].StartIdx < indices[j][0].StartIdx
-	})
-	toRet := make([]Match, 0, len(indices))
-	current := indices[0]
-	for _, idx := range indices[1:] {
-		// idx doesn't overlap with current (starts after current ends), so add current to result
-		// and update the current.
-		if idx[0].StartIdx >= current[0].EndIdx {
-			toRet = append(toRet, current)
-			current = idx
-		} else if idx[0].EndIdx > current[0].EndIdx {
-			// idx overlaps, but it is longer, so update current
-			current = idx
-		}
+// Find returns the 0-group of the leftmost match of the regex in the given string.
+// An error value != nil indicates that no match was found.
+func (re Reg) Find(str string) (Group, error) {
+	match, err := re.FindNthMatch(str, 1)
+	if err != nil {
+		return Group{}, fmt.Errorf("no matches found")
 	}
-	// Add last state
-	toRet = append(toRet, current)
-	return toRet
+	return getZeroGroup(match), nil
 }
 
-// FindString returns a _string_ containing the _text_ of the _leftmost_ match of
-// the regex, in the given string. The return value will be an empty string in two situations:
+// Match returns a boolean value, indicating whether the regex found a match in the given string.
+func (re Reg) Match(str string) bool {
+	_, err := re.Find(str)
+	return err == nil
+}
+
+// CompileMatch compiles expr and returns true if str contains a match of the expression.
+// It is equivalent to [regexp.Match].
+// An optional list of flags may be provided (see [ReFlag]).
+// It returns an error (!= nil) if there was an error compiling the expression.
+func CompileMatch(expr string, str string, flags ...ReFlag) (bool, error) {
+	re, err := Compile(expr, flags...)
+	if err != nil {
+		return false, err
+	}
+	return re.Match(str), nil
+}
+
+// FindAll returns a slice containing all the 0-groups of the regex in the given string.
+// A 0-group represents the match without any submatches.
+func (re Reg) FindAll(str string) []Group {
+	indices := re.FindAllSubmatch(str)
+	zeroGroups := funcMap(indices, getZeroGroup)
+	return zeroGroups
+}
+
+// FindString returns the text of the leftmost match of the regex in the given string.
+// The return value will be an empty string in two situations:
 //  1. No match was found
 //  2. The match was an empty string
-func FindString(regex Reg, str string) string {
-	match, err := FindNthMatch(regex, str, 1)
+func (re Reg) FindString(str string) string {
+	match, err := re.FindNthMatch(str, 1)
 	if err != nil {
 		return ""
 	}
-	return str[match[0].StartIdx:match[0].EndIdx]
+	zeroGroup := getZeroGroup(match)
+	return str[zeroGroup.StartIdx:zeroGroup.EndIdx]
 }
 
-// FindAllString is the 'all' version of FindString.
-// It returns a _slice of strings_ containing the _text_ of _all_ matches of
-// the regex, in the given string.
-//func FindAllString(regex Reg, str []string) []string {
-//
-//}
+// FindSubmatch returns the leftmost match of the regex in the given string, including
+// the submatches matched by capturing groups. The returned [Match] will always contain the same
+// number of groups. The validity of a group (whether or not it matched anything) can be determined with
+// [Group.IsValid], or by checking that both indices of the group are >= 0.
+// The second-return value is nil if no match was found.
+func (re Reg) FindSubmatch(str string) (Match, error) {
+	match, err := re.FindNthMatch(str, 1)
+	if err != nil {
+		return Match{}, fmt.Errorf("no match found")
+	} else {
+		return match, nil
+	}
+}
 
-// FindNthMatch finds the 'n'th match of the regex represented by the given start-state, with
-// the given string.
+// FindStringSubmatch is the 'string' version of [FindSubmatch]. It returns a slice of strings,
+// where the string at index i contains the text matched by the i-th capturing group.
+// The 0-th index represents the entire match.
+// An empty string at index n could mean:
+// ,
+//  1. Group n did not find a match
+//  2. Group n found a zero-length match
+//
+// A return value of nil indicates no match.
+func (re Reg) FindStringSubmatch(str string) []string {
+	matchStr := make([]string, re.numGroups+1)
+	match, err := re.FindSubmatch(str)
+	if err != nil {
+		return nil
+	}
+	nonEmptyMatchFound := false
+	for i := range match {
+		if match[i].IsValid() {
+			matchStr[i] = str[match[i].StartIdx:match[i].EndIdx]
+			nonEmptyMatchFound = true
+		} else {
+			matchStr[i] = ""
+		}
+	}
+	if nonEmptyMatchFound == false {
+		return nil
+	}
+	return matchStr
+}
+
+// FindAllString is the 'all' version of [FindString].
+// It returns a slice of strings containing the text of all matches of
+// the regex in the given string.
+func (re Reg) FindAllString(str string) []string {
+	zerogroups := re.FindAll(str)
+	matchStrs := funcMap(zerogroups, func(g Group) string {
+		return str[g.StartIdx:g.EndIdx]
+	})
+	return matchStrs
+}
+
+// FindNthMatch return the 'n'th match of the regex in the given string.
 // It returns an error (!= nil) if there are fewer than 'n' matches in the string.
-func FindNthMatch(regex Reg, str string, n int) (Match, error) {
+func (re Reg) FindNthMatch(str string, n int) (Match, error) {
 	idx := 0
 	matchNum := 0
 	str_runes := []rune(str)
 	var matchFound bool
 	var matchIdx Match
 	for idx <= len(str_runes) {
-		matchFound, matchIdx, idx = findAllMatchesHelper(regex.start, str_runes, idx, regex.numGroups)
+		matchFound, matchIdx, idx = findAllSubmatchHelper(re.start, str_runes, idx, re.numGroups, re.preferLongest)
 		if matchFound {
 			matchNum++
 		}
@@ -179,237 +188,273 @@ func FindNthMatch(regex Reg, str string, n int) (Match, error) {
 	return nil, fmt.Errorf("invalid match index - too few matches found")
 }
 
-// FindAllMatches tries to find all matches of the regex represented by given start-state, with
-// the given string
-func FindAllMatches(regex Reg, str string) []Match {
+// FindAllSubmatch returns a slice of matches in the given string.
+func (re Reg) FindAllSubmatch(str string) []Match {
 	idx := 0
 	str_runes := []rune(str)
 	var matchFound bool
 	var matchIdx Match
 	indices := make([]Match, 0)
 	for idx <= len(str_runes) {
-		matchFound, matchIdx, idx = findAllMatchesHelper(regex.start, str_runes, idx, regex.numGroups)
+		matchFound, matchIdx, idx = findAllSubmatchHelper(re.start, str_runes, idx, re.numGroups, re.preferLongest)
 		if matchFound {
 			indices = append(indices, matchIdx)
 		}
 	}
-	if len(indices) > 0 {
-		return pruneIndices(indices)
-	}
+
 	return indices
 }
 
+// FindAllSubmatch returns a double-slice of strings. Each slice contains the text of a match, including all submatches.
+// A return value of nil indicates no match.
+func (re Reg) FindAllStringSubmatch(str string) [][]string {
+	match := re.FindAllSubmatch(str)
+	if len(match) == 0 {
+		return nil
+	}
+	rtv := make([][]string, len(match))
+	for i := range rtv {
+		rtv[i] = make([]string, re.numGroups+1)
+	}
+	rtv = funcMap(match, func(m Match) []string {
+		return funcMap(m, func(g Group) string {
+			if g.IsValid() {
+				return str[g.StartIdx:g.EndIdx]
+			} else {
+				return ""
+			}
+		})
+	})
+	return rtv
+}
+
+func addStateToList(str []rune, idx int, list []nfaState, state nfaState, threadGroups []Group, visited []nfaState, preferLongest bool) []nfaState {
+	if stateExists(list, state) || stateExists(visited, state) {
+		return list
+	}
+	visited = append(visited, state)
+
+	if state.isKleene || state.isQuestion {
+		copyThread(state.splitState, state)
+		list = addStateToList(str, idx, list, *state.splitState, threadGroups, visited, preferLongest)
+		copyThread(state.next, state)
+		list = addStateToList(str, idx, list, *state.next, threadGroups, visited, preferLongest)
+		return list
+	}
+	if state.isAlternation {
+		copyThread(state.next, state)
+		list = addStateToList(str, idx, list, *state.next, threadGroups, visited, preferLongest)
+		copyThread(state.splitState, state)
+		list = addStateToList(str, idx, list, *state.splitState, threadGroups, visited, preferLongest)
+		return list
+	}
+	state.threadGroups = append([]Group{}, threadGroups...)
+	if state.assert != noneAssert {
+		if state.checkAssertion(str, idx, preferLongest) {
+			copyThread(state.next, state)
+			return addStateToList(str, idx, list, *state.next, state.threadGroups, visited, preferLongest)
+		}
+	}
+	if state.groupBegin {
+		state.threadGroups[state.groupNum].StartIdx = idx
+		return addStateToList(str, idx, list, *state.next, state.threadGroups, visited, preferLongest)
+	}
+	if state.groupEnd {
+		state.threadGroups[state.groupNum].EndIdx = idx
+		return addStateToList(str, idx, list, *state.next, state.threadGroups, visited, preferLongest)
+	}
+	return append(list, state)
+
+}
+
 // Helper for FindAllMatches. Returns whether it found a match, the
 // first Match it finds, and how far it got into the string ie. where
 // the next search should start from.
-//
-//	Might return duplicates or overlapping indices, so care must be taken to prune the resulting array.
-func findAllMatchesHelper(start *nfaState, str []rune, offset int, numGroups int) (bool, Match, int) {
+func findAllSubmatchHelper(start *nfaState, str []rune, offset int, numGroups int, preferLongest bool) (bool, Match, int) {
 	// Base case - exit if offset exceeds string's length
 	if offset > len(str) {
 		// The second value here shouldn't be used, because we should exit when the third return value is > than len(str)
 		return false, []Group{}, offset
 	}
+	resetThreads(start)
 
-	// Hold a list of match indices for the current run. When we
-	// can no longer find a match, the match with the largest range is
-	// chosen as the match for the entire string.
-	// This allows us to pick the longest possible match (which is how greedy matching works).
-	// COMMENT ABOVE IS CURRENTLY NOT UP-TO-DATE
-	tempIndices := newMatch(numGroups + 1)
-
-	foundPath := false
-	startIdx := offset
-	endIdx := offset
-	currentStates := make([]*nfaState, 0)
-	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
+	currentStates := make([]nfaState, 0)
+	nextStates := make([]nfaState, 0)
+	i := offset // Index in string
 
 	// If the first state is an assertion, makes sure the assertion
 	// is true before we do _anything_ else.
 	if start.assert != noneAssert {
-		if start.checkAssertion(str, offset) == false {
+		if start.checkAssertion(str, offset, preferLongest) == false {
 			i++
 			return false, []Group{}, i
 		}
 	}
-	// Increment until we hit a character matching the start state (assuming not 0-state)
-	if start.isEmpty == false {
-		for i < len(str) && !start.contentContains(str, i) {
-			i++
-		}
-		startIdx = i
-		startingFrom = i
-		i++ // Advance to next character (if we aren't at a 0-state, which doesn't match anything), so that we can check for transitions. If we advance at a 0-state, we will never get a chance to match the first character
-	}
 
 	start.threadGroups = newMatch(numGroups + 1)
-	// Check if the start state begins a group - if so, add the start index to our list
-	if start.groupBegin {
-		start.threadGroups[start.groupNum].StartIdx = i
-		//		tempIndices[start.groupNum].startIdx = i
-	}
-
-	currentStates = append(currentStates, start)
-
-	// Main loop
-	for i < len(str) {
-		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)
-		tempStates = append(tempStates, zeroStates...)
-		num_appended := 0
-		for isZero == true {
-			zeroStates, isZero = takeZeroState(tempStates, numGroups, i)
-			tempStates, num_appended = unique_append(tempStates, zeroStates...)
-			if num_appended == 0 { // Break if we haven't appended any more unique values
-				break
-			}
-		}
-
-		currentStates, _ = unique_append(currentStates, tempStates...)
-		tempStates = nil
-
-		// Take any transitions corresponding to current character
-		numStatesMatched := 0            // The number of states which had at least 1 match for this round
-		assertionFailed := false         // Whether or not an assertion failed for this round
-		lastStateInList := false         // Whether or not a last state was in our list of states
-		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 _, state := range currentStates {
-			matches, numMatches := state.matchesFor(str, i)
-			if numMatches > 0 {
-				numStatesMatched++
-				tempStates = append(tempStates, matches...)
-				foundPath = true
-				for _, m := range matches {
-					if m.threadGroups == nil {
-						m.threadGroups = newMatch(numGroups + 1)
-					}
-					copy(m.threadGroups, state.threadGroups)
-				}
-			}
-			if numMatches < 0 {
-				assertionFailed = true
-			}
-			if state.isLast {
-				if state.isLookaround() {
-					lastLookaroundInList = true
-				}
-				lastStateInList = true
-				lastStatePtr = state
-			}
-		}
-
-		if assertionFailed && numStatesMatched == 0 { // Nothing has matched and an assertion has failed
-			// If I'm being completely honest, I'm not sure why I have to check specifically for a _lookaround_
-			// state. The explanation below is my attempt to explain this behavior.
-			// If you replace 'lastLookaroundInList' with 'lastStateInList', one of the test cases fails.
-			//
-			// One of the states in our list was a last state and a lookaround. In this case, we
-			// don't abort upon failure of the assertion, because we have found
-			// another path to a final state.
-			// Even if the last state _was_ an assertion, we can use the previously
-			// saved indices to find a match.
-			if lastLookaroundInList {
-				break
-			} else {
-				if i == startingFrom {
-					i++
-				}
-				return false, []Group{}, i
-			}
-		}
-		// Check if we can find a state in our list that is:
-		// 	a. A last-state
-		// 	b. Empty
-		// 	c. Doesn't assert anything
-		for _, s := range currentStates {
-			if s.isLast && s.isEmpty && s.assert == noneAssert {
-				lastStatePtr = s
-				lastStateInList = true
-			}
-		}
-		if lastStateInList { // A last-state was in the list of states. add the matchIndex to our MatchIndex list
-			for j := 1; j < numGroups+1; j++ {
-				tempIndices[j] = lastStatePtr.threadGroups[j]
-			}
-			endIdx = i
-			tempIndices[0] = Group{startIdx, endIdx}
-		}
-
-		// Check if we can find a zero-length match
-		if foundPath == false {
-			if ok := zeroMatchPossible(str, i, numGroups, currentStates...); ok {
-				if tempIndices[0].isValid() == false {
-					tempIndices[0] = Group{startIdx, startIdx}
-				}
-			}
-			// If we haven't moved in the string, increment the counter by 1
-			// to ensure we don't keep trying the same string over and over.
-			//			if i == startingFrom {
-			startIdx++
-			//	i++
-			//			}
-			if tempIndices.numValidGroups() > 0 && tempIndices[0].isValid() {
-				if tempIndices[0].StartIdx == tempIndices[0].EndIdx { // If we have a zero-length match, we have to shift the index at which we start. Otherwise we keep looking at the same paert of the string over and over.
-					return true, tempIndices, tempIndices[0].EndIdx + 1
-				} else {
-					return true, tempIndices, tempIndices[0].EndIdx
-				}
-			}
-			return false, []Group{}, startIdx
-		}
-		currentStates = make([]*nfaState, len(tempStates))
-		copy(currentStates, tempStates)
-		tempStates = nil
-
-		i++
-	}
-
-	// 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)
-	tempStates = append(tempStates, zeroStates...)
-	num_appended := 0 // Number of unique states addded to tempStates
-	for isZero == true {
-		zeroStates, isZero = takeZeroState(tempStates, numGroups, i)
-		tempStates, num_appended = unique_append(tempStates, zeroStates...)
-		if num_appended == 0 { // Break if we haven't appended any more unique values
+	start.threadGroups[0].StartIdx = i
+	currentStates = addStateToList(str, i, currentStates, *start, start.threadGroups, nil, preferLongest)
+	var match Match = nil
+	for idx := i; idx <= len(str); idx++ {
+		if len(currentStates) == 0 {
 			break
 		}
-	}
+		for currentStateIdx := 0; currentStateIdx < len(currentStates); currentStateIdx++ {
+			currentState := currentStates[currentStateIdx]
 
-	currentStates = append(currentStates, tempStates...)
-	tempStates = nil
+			if currentState.threadGroups == nil {
+				currentState.threadGroups = newMatch(numGroups + 1)
+				currentState.threadGroups[0].StartIdx = idx
+			}
 
-	for _, state := range currentStates {
-		// 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) {
-			if state.assert == noneAssert || state.checkAssertion(str, i) {
-				for j := 1; j < numGroups+1; j++ {
-					tempIndices[j] = state.threadGroups[j]
+			if currentState.isLast {
+				currentState.threadGroups[0].EndIdx = idx
+				match = append([]Group{}, currentState.threadGroups...)
+				if !preferLongest {
+					break
+				}
+			} else if !currentState.isAlternation && !currentState.isKleene && !currentState.isQuestion && !currentState.groupBegin && !currentState.groupEnd && currentState.assert == noneAssert { // Normal character
+				if currentState.contentContains(str, idx, preferLongest) {
+					nextStates = addStateToList(str, idx+1, nextStates, *currentState.next, currentState.threadGroups, nil, preferLongest)
 				}
-				endIdx = i
-				tempIndices[0] = Group{startIdx, endIdx}
 			}
 		}
+		currentStates = append([]nfaState{}, nextStates...)
+		nextStates = nil
 	}
+	if match != nil {
+		if offset == match[0].EndIdx {
+			return true, match, match[0].EndIdx + 1
+		}
+		return true, match, match[0].EndIdx
+	}
+	return false, []Group{}, i + 1
+}
 
-	if tempIndices.numValidGroups() > 0 {
-		if tempIndices[0].StartIdx == tempIndices[0].EndIdx { // If we have a zero-length match, we have to shift the index at which we start. Otherwise we keep looking at the same paert of the string over and over.
-			return true, tempIndices, tempIndices[0].EndIdx + 1
+// Expand appends template to dst, expanding any variables in template to the relevant capturing group.
+//
+// A variable is of the form '$n', where 'n' is a number. It will be replaced by the contents of the n-th capturing group.
+// To insert a literal $, do not put a number after it. Alternatively, you can use $$.
+// src is the input string, and match must be the result of [Reg.FindSubmatch].
+func (re Reg) Expand(dst string, template string, src string, match Match) string {
+	templateRuneSlc := []rune(template)
+	srcRuneSlc := []rune(src)
+	i := 0
+	for i < len(templateRuneSlc) {
+		c := templateRuneSlc[i]
+		if c == '$' {
+			i += 1
+			// The dollar sign is the last character of the string, or it is proceeded by another dollar sign
+			if i >= len(templateRuneSlc) || templateRuneSlc[i] == '$' {
+				dst += "$"
+				i++
+			} else {
+				numStr := ""
+				for i < len(templateRuneSlc) && unicode.IsDigit(templateRuneSlc[i]) {
+					numStr += string(templateRuneSlc[i])
+					i++
+				}
+				if numStr == "" {
+					dst += "$"
+				} else {
+					num, _ := strconv.Atoi(numStr)
+					if num < len(match) {
+						dst += string(srcRuneSlc[match[num].StartIdx:match[num].EndIdx])
+					} else {
+						dst += "$" + numStr
+					}
+				}
+			}
 		} else {
-			return true, tempIndices, tempIndices[0].EndIdx
+			dst += string(c)
+			i++
 		}
 	}
-	if startIdx == startingFrom { // Increment starting index if we haven't moved in the string. Prevents us from matching the same part of the string over and over.
-		startIdx++
-	}
-	return false, []Group{}, startIdx
+	return dst
+}
+
+// LiteralPrefix returns a string that must begin any match of the given regular expression.
+// The second return value is true if the string comprises the entire expression.
+func (re Reg) LiteralPrefix() (prefix string, complete bool) {
+	state := re.start
+	if state.assert != noneAssert {
+		state = state.next
+	}
+	for !(state.isLast) && (!state.isAlternation) && len(state.content) == 1 && state.assert == noneAssert {
+		if state.groupBegin || state.groupEnd {
+			state = state.next
+			continue
+		}
+		prefix += string(rune(state.content[0]))
+		state = state.next
+	}
+	if state.isLast {
+		complete = true
+	} else {
+		complete = false
+	}
+	return prefix, complete
+}
+
+// ReplaceAll replaces all matches of the expression in src, with the text in repl. In repl, variables are interpreted
+// as they are in [Reg.Expand]. The resulting string is returned.
+func (re Reg) ReplaceAll(src string, repl string) string {
+	matches := re.FindAllSubmatch(src)
+	i := 0
+	currentMatch := 0
+	dst := ""
+	for i < len(src) {
+		if currentMatch < len(matches) && matches[currentMatch][0].IsValid() && i == matches[currentMatch][0].StartIdx {
+			dst += re.Expand("", repl, src, matches[currentMatch])
+			i = matches[currentMatch][0].EndIdx
+			currentMatch++
+		} else {
+			dst += string(src[i])
+			i++
+		}
+	}
+	return dst
+}
+
+// ReplaceAllLiteral replaces all matches of the expression in src, with the text in repl. The text is replaced directly,
+// without any expansion.
+func (re Reg) ReplaceAllLiteral(src string, repl string) string {
+	zerogroups := re.FindAll(src)
+	currentMatch := 0
+	i := 0
+	dst := ""
+
+	for i < len(src) {
+		if currentMatch < len(zerogroups) && i == zerogroups[currentMatch].StartIdx {
+			dst += repl
+			i = zerogroups[currentMatch].EndIdx
+			currentMatch += 1
+		} else {
+			dst += string(src[i])
+			i++
+		}
+	}
+	return dst
+}
+
+// ReplaceAllFunc replaces every match of the expression in src, with the return value of the function replFunc.
+// replFunc takes in the matched string. The return value is substituted in directly without expasion.
+func (re Reg) ReplaceAllFunc(src string, replFunc func(string) string) string {
+	zerogroups := re.FindAll(src)
+	currentMatch := 0
+	i := 0
+	dst := ""
+
+	for i < len(src) {
+		if currentMatch < len(zerogroups) && i == zerogroups[currentMatch].StartIdx {
+			dst += replFunc(src[zerogroups[currentMatch].StartIdx:zerogroups[currentMatch].EndIdx])
+			i = zerogroups[currentMatch].EndIdx
+			currentMatch += 1
+		} else {
+			dst += string(src[i])
+			i++
+		}
+	}
+	return dst
+
 }

regex/misc.go

@@ -48,30 +48,6 @@ func isNormalChar(c rune) bool {
 	return !slices.Contains(specialChars, c)
 }
 
-// Ensure that the given elements are only appended to the given slice if they
-// don't already exist. Returns the new slice, and the number of unique items appended.
-func unique_append[T comparable](slc []T, items ...T) ([]T, int) {
-	num_appended := 0
-	for _, item := range items {
-		if !slices.Contains(slc, item) {
-			slc = append(slc, item)
-			num_appended++
-		}
-	}
-	return slc, num_appended
-}
-
-// Returns true only if all the given elements are equal
-func allEqual[T comparable](items ...T) bool {
-	first := items[0]
-	for _, item := range items {
-		if item != first {
-			return false
-		}
-	}
-	return true
-}
-
 // Map function - convert a slice of T to a slice of V, based on a function
 // that maps a T to a V
 func funcMap[T, V any](slc []T, fn func(T) V) []V {

regex/nfa.go

@@ -25,21 +25,25 @@ const (
 )
 
 type nfaState 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                     []*nfaState         // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
-	transitions                map[int][]*nfaState // 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              *nfaState           // 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
+	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  []*nfaState   // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
+	//	transitions                map[int][]*nfaState // 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)
+	next                       *nfaState  // The next state (not for alternation or kleene states)
+	isKleene                   bool       // Identifies whether current node is a 0-state representing Kleene star
+	isQuestion                 bool       // Identifies whether current node is a 0-state representing the question operator
+	isAlternation              bool       // Identifies whether current node is a 0-state representing an alternation
+	splitState                 *nfaState  // Only for alternation states - the 'other' branch of the alternation ('next' is the first)
+	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              *nfaState  // 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.
@@ -68,8 +72,9 @@ func cloneStateHelper(stateToClone *nfaState, cloneMap map[*nfaState]*nfaState)
 		isEmpty:         stateToClone.isEmpty,
 		isLast:          stateToClone.isLast,
 		output:          make([]*nfaState, len(stateToClone.output)),
-		transitions:     make(map[int][]*nfaState),
 		isKleene:        stateToClone.isKleene,
+		isQuestion:      stateToClone.isQuestion,
+		isAlternation:   stateToClone.isAlternation,
 		assert:          stateToClone.assert,
 		zeroMatchFound:  stateToClone.zeroMatchFound,
 		allChars:        stateToClone.allChars,
@@ -87,26 +92,48 @@ func cloneStateHelper(stateToClone *nfaState, cloneMap map[*nfaState]*nfaState)
 			clone.output[i] = cloneStateHelper(s, cloneMap)
 		}
 	}
-	for k, v := range stateToClone.transitions {
-		clone.transitions[k] = make([]*nfaState, len(v))
-		for i, s := range v {
-			if s == stateToClone {
-				clone.transitions[k][i] = clone
-			} else {
-				clone.transitions[k][i] = cloneStateHelper(s, cloneMap)
-			}
-		}
-	}
 	if stateToClone.lookaroundNFA == stateToClone {
 		clone.lookaroundNFA = clone
 	}
 	clone.lookaroundNFA = cloneStateHelper(stateToClone.lookaroundNFA, cloneMap)
+	if stateToClone.splitState == stateToClone {
+		clone.splitState = clone
+	}
+	clone.splitState = cloneStateHelper(stateToClone.splitState, cloneMap)
+	if stateToClone.next == stateToClone {
+		clone.next = clone
+	}
+	clone.next = cloneStateHelper(stateToClone.next, cloneMap)
 	return clone
 }
 
+// Reset any thread-related fields of the NFA starting from the given state.
+func resetThreads(start *nfaState) {
+	visitedMap := make(map[*nfaState]bool) // The value type doesn't matter here
+	resetThreadsHelper(start, visitedMap)
+}
+
+func resetThreadsHelper(state *nfaState, visitedMap map[*nfaState]bool) {
+	if state == nil {
+		return
+	}
+	if _, ok := visitedMap[state]; ok {
+		return
+	}
+	// Assuming it hasn't been visited
+	state.threadGroups = nil
+	visitedMap[state] = true
+	if state.isAlternation {
+		resetThreadsHelper(state.next, visitedMap)
+		resetThreadsHelper(state.splitState, visitedMap)
+	} else {
+		resetThreadsHelper(state.next, visitedMap)
+	}
+}
+
 // Checks if the given state's assertion is true. Returns true if the given
 // state doesn't have an assertion.
-func (s nfaState) checkAssertion(str []rune, idx int) bool {
+func (s nfaState) checkAssertion(str []rune, idx int, preferLongest bool) bool {
 	if s.assert == alwaysTrueAssert {
 		return true
 	}
@@ -156,17 +183,18 @@ func (s nfaState) checkAssertion(str []rune, idx int) bool {
 			strToMatch = string(runesToMatch)
 		}
 
-		matchIndices := FindAllMatches(Reg{startState, s.lookaroundNumCaptureGroups}, strToMatch)
+		regComp := Reg{startState, s.lookaroundNumCaptureGroups, s.lookaroundRegex, preferLongest}
+		matchIndices := regComp.FindAll(strToMatch)
 
 		numMatchesFound := 0
 		for _, matchIdx := range matchIndices {
 			if s.assert == plaAssert || s.assert == nlaAssert { // 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 {
+				if matchIdx.StartIdx == 0 {
 					numMatchesFound++
 				}
 			}
 			if s.assert == plbAssert || s.assert == nlbAssert { // Lookbehind - return true (or false) if at least one match _ends_ at the current index.
-				if matchIdx[0].EndIdx == idx {
+				if matchIdx.EndIdx == idx {
 					numMatchesFound++
 				}
 			}
@@ -182,9 +210,12 @@ func (s nfaState) checkAssertion(str []rune, idx int) bool {
 }
 
 // Returns true if the contents of 's' contain the value at the given index of the given string
-func (s nfaState) contentContains(str []rune, idx int) bool {
+func (s nfaState) contentContains(str []rune, idx int, preferLongest bool) bool {
 	if s.assert != noneAssert {
-		return s.checkAssertion(str, idx)
+		return s.checkAssertion(str, idx, preferLongest)
+	}
+	if idx >= len(str) {
+		return false
 	}
 	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.
@@ -197,74 +228,84 @@ func (s nfaState) isLookaround() bool {
 	return s.assert == plaAssert || s.assert == plbAssert || s.assert == nlaAssert || s.assert == nlbAssert
 }
 
+func (s nfaState) numTransitions() int {
+	if s.next == nil && s.splitState == nil {
+		return 0
+	}
+	if s.next == nil || s.splitState == nil {
+		return 1
+	}
+	return 2
+}
+
 // 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 nfaState) matchesFor(str []rune, idx int) ([]*nfaState, 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 != noneAssert {
-		if s.checkAssertion(str, idx) == false {
-			return make([]*nfaState, 0), -1
-		}
-	}
-	listTransitions := s.transitions[int(str[idx])]
-	for _, dest := range s.transitions[int(anyCharRune)] {
-		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
-}
+//func (s nfaState) matchesFor(str []rune, idx int) ([]*nfaState, 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 != noneAssert {
+//		if s.checkAssertion(str, idx) == false {
+//			return make([]*nfaState, 0), -1
+//		}
+//	}
+//	listTransitions := s.transitions[int(str[idx])]
+//	for _, dest := range s.transitions[int(anyCharRune)] {
+//		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(st *nfaState, visited map[*nfaState]bool) {
-	if len(st.transitions) == 0 {
-		st.isLast = true
-		return
-	}
-	//	if len(state.transitions) == 1 && len(state.transitions[state.content]) == 1 && state.transitions[state.content][0] == state { // Eg. a*
-	if len(st.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 st.content {
-			if len(st.transitions[c]) != 1 || st.transitions[c][0] != st {
-				moreThanOneTrans = true
-			}
-		}
-		st.isLast = !moreThanOneTrans
-	}
-
-	if st.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([]*nfaState, 0)
-		for _, v := range st.transitions {
-			transitionDests = append(transitionDests, v...)
-		}
-		if allEqual(transitionDests...) {
-			st.isLast = true
-			return
-		}
-	}
-	if visited[st] == true {
-		return
-	}
-	visited[st] = true
-	for _, states := range st.transitions {
-		for i := range states {
-			if states[i] != st {
-				verifyLastStatesHelper(states[i], visited)
-			}
-		}
-	}
-}
+//func verifyLastStatesHelper(st *nfaState, visited map[*nfaState]bool) {
+//	if st.numTransitions() == 0 {
+//		st.isLast = true
+//		return
+//	}
+//	//	if len(state.transitions) == 1 && len(state.transitions[state.content]) == 1 && state.transitions[state.content][0] == state { // Eg. a*
+//	if st.numTransitions() == 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 st.content {
+//			if len(st.transitions[c]) != 1 || st.transitions[c][0] != st {
+//				moreThanOneTrans = true
+//			}
+//		}
+//		st.isLast = !moreThanOneTrans
+//	}
+//
+//	if st.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([]*nfaState, 0)
+//		for _, v := range st.transitions {
+//			transitionDests = append(transitionDests, v...)
+//		}
+//		if allEqual(transitionDests...) {
+//			st.isLast = true
+//			return
+//		}
+//	}
+//	if visited[st] == true {
+//		return
+//	}
+//	visited[st] = true
+//	for _, states := range st.transitions {
+//		for i := range states {
+//			if states[i] != st {
+//				verifyLastStatesHelper(states[i], visited)
+//			}
+//		}
+//	}
+//}
 
 // verifyLastStates enables the 'isLast' flag for the leaf nodes (last states)
-func verifyLastStates(start []*nfaState) {
-	verifyLastStatesHelper(start[0], make(map[*nfaState]bool))
-}
+//func verifyLastStates(start []*nfaState) {
+//	verifyLastStatesHelper(start[0], make(map[*nfaState]bool))
+//}
 
 // Concatenates s1 and s2, returns the start of the concatenation.
 func concatenate(s1 *nfaState, s2 *nfaState) *nfaState {
@@ -272,73 +313,84 @@ func concatenate(s1 *nfaState, s2 *nfaState) *nfaState {
 		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[i].next = s2
 	}
 	s1.output = s2.output
 	return s1
 }
 
-func kleene(s1 nfaState) (*nfaState, error) {
+func kleene(s1 *nfaState) (*nfaState, error) {
 	if s1.isEmpty && s1.assert != noneAssert {
 		return nil, fmt.Errorf("previous token is not quantifiable")
 	}
 
 	toReturn := &nfaState{}
-	toReturn.transitions = make(map[int][]*nfaState)
-	toReturn.content = newContents(epsilon)
 	toReturn.isEmpty = true
+	toReturn.isAlternation = true
+	toReturn.content = newContents(epsilon)
+	toReturn.splitState = s1
+
+	//	toReturn := &nfaState{}
+	//	toReturn.transitions = make(map[int][]*nfaState)
+	//	toReturn.content = newContents(epsilon)
 	toReturn.isKleene = true
-	toReturn.output = append(toReturn.output, toReturn)
+	toReturn.output = append([]*nfaState{}, 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)
+		s1.output[i].next = toReturn
 	}
+	//	for _, c := range s1.content {
+	//		toReturn.transitions[c], _ = uniqueAppend(toReturn.transitions[c], &s1)
+	//	}
+	//toReturn.kleeneState = &s1
 	return toReturn, nil
 }
 
 func alternate(s1 *nfaState, s2 *nfaState) *nfaState {
 	toReturn := &nfaState{}
-	toReturn.transitions = make(map[int][]*nfaState)
+	//	toReturn.transitions = make(map[int][]*nfaState)
 	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)
-	}
+	//	// 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], _ = uniqueAppend(toReturn.transitions[c], s1)
+	//	}
+	//	for _, c := range s2.content {
+	//		toReturn.transitions[c], _ = uniqueAppend(toReturn.transitions[c], s2)
+	//	}
 	toReturn.content = newContents(epsilon)
 	toReturn.isEmpty = true
+	toReturn.isAlternation = true
+	toReturn.next = s1
+	toReturn.splitState = s2
 
 	return toReturn
 }
 
-func question(s1 *nfaState) *nfaState { // Use the fact that ab? == a(b|)
-	s2 := &nfaState{}
-	s2.transitions = make(map[int][]*nfaState)
-	s2.content = newContents(epsilon)
-	s2.output = append(s2.output, s2)
-	s2.isEmpty = true
-	s3 := alternate(s1, s2)
-	return s3
+func question(s1 *nfaState) (*nfaState, error) { // Use the fact that ab? == a(b|)
+	if s1.isEmpty && s1.assert != noneAssert {
+		return nil, fmt.Errorf("previous token is not quantifiable")
+	}
+	toReturn := &nfaState{}
+	toReturn.isEmpty = true
+	toReturn.isAlternation = true
+	toReturn.isQuestion = true
+	toReturn.content = newContents(epsilon)
+	toReturn.splitState = s1
+	toReturn.output = append([]*nfaState{}, toReturn)
+	toReturn.output = append(toReturn.output, s1.output...)
+	//	s2.transitions = make(map[int][]*nfaState)
+	return toReturn, nil
 }
 
 // Creates and returns a new state with the 'default' values.
 func newState() nfaState {
 	ret := nfaState{
-		output:          make([]*nfaState, 0),
-		transitions:     make(map[int][]*nfaState),
+		output: make([]*nfaState, 0),
+		//		transitions:     make(map[int][]*nfaState),
 		assert:          noneAssert,
 		except:          append([]rune{}, 0),
 		lookaroundRegex: "",
@@ -350,10 +402,40 @@ func newState() nfaState {
 }
 
 // Creates and returns a state that _always_ has a zero-length match.
-func zeroLengthMatchState() nfaState {
-	start := newState()
+func zeroLengthMatchState() *nfaState {
+	start := &nfaState{}
 	start.content = newContents(epsilon)
 	start.isEmpty = true
 	start.assert = alwaysTrueAssert
+	start.output = append([]*nfaState{}, start)
 	return start
 }
+
+func (s nfaState) equals(other nfaState) bool {
+	return s.isEmpty == other.isEmpty &&
+		s.isLast == other.isLast &&
+		slices.Equal(s.output, other.output) &&
+		slices.Equal(s.content, other.content) &&
+		s.next == other.next &&
+		s.isKleene == other.isKleene &&
+		s.isQuestion == other.isQuestion &&
+		s.isAlternation == other.isAlternation &&
+		s.splitState == other.splitState &&
+		s.assert == other.assert &&
+		s.allChars == other.allChars &&
+		slices.Equal(s.except, other.except) &&
+		s.lookaroundNFA == other.lookaroundNFA &&
+		s.groupBegin == other.groupBegin &&
+		s.groupEnd == other.groupEnd &&
+		s.groupNum == other.groupNum &&
+		slices.Equal(s.threadGroups, other.threadGroups)
+}
+
+func stateExists(list []nfaState, s nfaState) bool {
+	for i := range list {
+		if list[i].equals(s) {
+			return true
+		}
+	}
+	return false
+}

regex/range2regex.go

@@ -3,7 +3,9 @@ package regex
 import (
 	"fmt"
 	"math"
+	"slices"
 	"strconv"
+	"strings"
 )
 
 type numRange struct {
@@ -99,28 +101,39 @@ func range2regex(start int, end int) (string, error) {
 	// Last range - tmp to rangeEnd
 	ranges = append(ranges, numRange{tmp, rangeEnd})
 
-	regex := string(nonCapLparenRune)
+	regexSlice := make([]string, 0)
 	// Generate the regex
-	for i, rg := range ranges {
-		if i > 0 {
-			regex += "|"
-		}
-		regex += string(nonCapLparenRune)
+	for _, rg := range ranges {
+		tmpStr := ""
+		tmpStr += string(nonCapLparenRune)
 		startSlc := intToSlc(rg.start)
 		endSlc := intToSlc(rg.end)
 		if len(startSlc) != len(endSlc) {
-			return "", fmt.Errorf("Error parsing numeric range")
+			return "", fmt.Errorf("error parsing numeric range")
 		}
 		for i := range startSlc {
 			if startSlc[i] == endSlc[i] {
-				regex += string(rune(startSlc[i] + 48)) // '0' is ascii value 48, 1 is 49 etc. To convert the digit to its character form, we can just add 48.
+				tmpStr += string(rune(startSlc[i] + 48)) // '0' is ascii value 48, 1 is 49 etc. To convert the digit to its character form, we can just add 48.
 			} else {
-				regex += fmt.Sprintf("%c%c-%c%c", lbracketRune, rune(startSlc[i]+48), rune(endSlc[i]+48), rbracketRune)
+				tmpStr += fmt.Sprintf("%c%c-%c%c", lbracketRune, rune(startSlc[i]+48), rune(endSlc[i]+48), rbracketRune)
 			}
 		}
-		regex += ")"
+		tmpStr += ")"
+		regexSlice = append(regexSlice, tmpStr)
 	}
-	regex += ")"
+	// Each element of the slice represents one 'group'. Taking 0-255 as an example, the elements would be:
+	// 	1. 0-9
+	// 	2. 10-99
+	// 	3. 100-199
+	// 	4. 200-249
+	// 	5. 250-255
+	//
+	// The reason this is reversed before joining it, is because it is incompatible with the PCRE rule for matching.
+	// The PCRE rule specifies that the left-branch of an alternation is preferred. Even though this engine uses the POSIX
+	// rule at the moment (which prefers the longest match regardless of the order of the alternation), reversing the string
+	// has no downsides. It doesn't affect POSIX matching, and it will reduce my burden if I decide to switch to PCRE matching.
+	slices.Reverse(regexSlice)
+	regex := string(nonCapLparenRune) + strings.Join(regexSlice, "|") + ")"
 	return regex, nil
 
 }

regex/re_test.go

@@ -25,7 +25,9 @@ var reTests = []struct {
 	{"a*b", nil, "qwqw", []Group{}},
 	{"(abc)*", nil, "abcabcabc", []Group{{0, 9}, {9, 9}}},
 	{"((abc)|(def))*", nil, "abcdef", []Group{{0, 6}, {6, 6}}},
-	{"(abc)*|(def)*", nil, "abcdef", []Group{{0, 3}, {3, 6}, {6, 6}}},
+	// This match will only happen with Longest()
+	// {"(abc)*|(def)*", nil, "abcdef", []Group{{0, 3}, {3, 6}, {6, 6}}},
+	{"(abc)*|(def)*", nil, "abcdef", []Group{{0, 3}, {3, 3}, {4, 4}, {5, 5}, {6, 6}}},
 	{"b*a*a", nil, "bba", []Group{{0, 3}}},
 	{"(ab)+", nil, "abcabddd", []Group{{0, 2}, {3, 5}}},
 	{"a(b(c|d)*)*", nil, "abccbd", []Group{{0, 6}}},
@@ -105,6 +107,9 @@ var reTests = []struct {
 	{"(a|b){3,4}", nil, "ababaa", []Group{{0, 4}}},
 	{"(bc){5,}", nil, "bcbcbcbcbcbcbcbc", []Group{{0, 16}}},
 	{`\d{3,4}`, nil, "1209", []Group{{0, 4}}},
+	{`\d{3,4}`, nil, "120", []Group{{0, 3}}},
+	{`\d{3,4}`, nil, "12709", []Group{{0, 4}}},
+	{`\d{3,4}`, nil, "12", []Group{}},
 	{`\d{3,4}`, nil, "109", []Group{{0, 3}}},
 	{`\d{3,4}`, nil, "5", []Group{}},
 	{`\d{3,4}`, nil, "123135", []Group{{0, 4}}},
@@ -525,7 +530,7 @@ var groupTests = []struct {
 }{
 	{"(a)(b)", nil, "ab", []Match{[]Group{{0, 2}, {0, 1}, {1, 2}}}},
 	{"((a))(b)", nil, "ab", []Match{[]Group{{0, 2}, {0, 1}, {0, 1}, {1, 2}}}},
-	{"(0)", nil, "ab", []Match{[]Group{}}},
+	{"(0)", nil, "ab", []Match{}},
 	{"(a)b", nil, "ab", []Match{[]Group{{0, 2}, {0, 1}}}},
 	{"a(b)", nil, "ab", []Match{[]Group{{0, 2}, {1, 2}}}},
 	{"(a|b)", nil, "ab", []Match{[]Group{{0, 1}, {0, 1}}, []Group{{1, 2}, {1, 2}}}},
@@ -534,10 +539,11 @@ var groupTests = []struct {
 	{"(a+)|(a)", nil, "aaaa", []Match{[]Group{{0, 4}, {0, 4}, {-1, -1}}}},
 	{"(a+)(aa)", nil, "aaaa", []Match{[]Group{{0, 4}, {0, 2}, {2, 4}}}},
 	{"(aaaa)|(aaaa)", nil, "aaaa", []Match{[]Group{{0, 4}, {0, 4}, {-1, -1}}}},
-	{"(aaa)|(aaaa)", nil, "aaaa", []Match{[]Group{{0, 4}, {-1, -1}, {0, 4}}}},
-	{"(aaa)|(aaaa)", nil, "aaaa", []Match{[]Group{{0, 4}, {-1, -1}, {0, 4}}}},
+	// This match will only happen with Longest()
+	//	{"(aaa)|(aaaa)", nil, "aaaa", []Match{[]Group{{0, 4}, {-1, -1}, {0, 4}}}},
+	{"(aaa)|(aaaa)", nil, "aaaa", []Match{[]Group{{0, 3}, {0, 3}, {-1, -1}}}},
 	{"(aaaa)|(aaa)", nil, "aaaa", []Match{[]Group{{0, 4}, {0, 4}, {-1, -1}}}},
-	{"(a)|(aa)", nil, "aa", []Match{[]Group{{0, 2}, {-1, -1}, {0, 2}}}},
+	{"(a)|(aa)", nil, "aa", []Match{[]Group{{0, 1}, {0, 1}}, []Group{{1, 2}, {1, 2}}}},
 	{"(a?)a?", nil, "b", []Match{[]Group{{0, 0}, {0, 0}}, []Group{{1, 1}, {1, 1}}}},
 	{"(a?)a?", nil, "ab", []Match{[]Group{{0, 1}, {0, 1}}, []Group{{1, 1}, {1, 1}}, []Group{{2, 2}, {2, 2}}}},
 	{"(a?)a?", nil, "aa", []Match{[]Group{{0, 2}, {0, 1}}, []Group{{2, 2}, {2, 2}}}},
@@ -575,7 +581,7 @@ var groupTests = []struct {
 	{`(bc+d$|ef*g.|h?i(j|k))`, nil, `bcdd`, []Match{}},
 	{`(bc+d$|ef*g.|h?i(j|k))`, nil, `reffgz`, []Match{[]Group{{1, 6}, {1, 6}}}},
 	{`(((((((((a)))))))))`, nil, `a`, []Match{[]Group{{0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
-	{`(((((((((a)))))))))\41`, nil, `a`, []Match{[]Group{{0, 2}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
+	{`(((((((((a)))))))))\41`, nil, `a!`, []Match{[]Group{{0, 2}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
 	{`(.*)c(.*)`, nil, `abcde`, []Match{[]Group{{0, 5}, {0, 2}, {3, 5}}}},
 	{`\((.*), (.*)\)`, nil, `(a, b)`, []Match{[]Group{{0, 6}, {1, 2}, {4, 5}}}},
 
@@ -630,7 +636,7 @@ var groupTests = []struct {
 	{`(bc+d$|ef*g.|h?i(j|k))`, []ReFlag{RE_CASE_INSENSITIVE}, `BCDD`, []Match{}},
 	{`(bc+d$|ef*g.|h?i(j|k))`, []ReFlag{RE_CASE_INSENSITIVE}, `reffgz`, []Match{[]Group{{1, 6}, {1, 6}}}},
 	{`(((((((((a)))))))))`, []ReFlag{RE_CASE_INSENSITIVE}, `A`, []Match{[]Group{{0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
-	{`(((((((((a)))))))))\41`, []ReFlag{RE_CASE_INSENSITIVE}, `A`, []Match{[]Group{{0, 2}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
+	{`(((((((((a)))))))))\41`, []ReFlag{RE_CASE_INSENSITIVE}, `A!`, []Match{[]Group{{0, 2}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}, {0, 1}}}},
 	{`(.*)c(.*)`, []ReFlag{RE_CASE_INSENSITIVE}, `ABCDE`, []Match{[]Group{{0, 5}, {0, 2}, {3, 5}}}},
 	{`\((.*), (.*)\)`, []ReFlag{RE_CASE_INSENSITIVE}, `(A, B)`, []Match{[]Group{{0, 6}, {1, 2}, {4, 5}}}},
 	{`(a)(b)c|ab`, []ReFlag{RE_CASE_INSENSITIVE}, `AB`, []Match{[]Group{{0, 2}}}},
@@ -671,9 +677,20 @@ var groupTests = []struct {
 	{`^([ab]*)(?<!(a))c`, nil, `abc`, []Match{[]Group{{0, 3}, {0, 2}}}},
 
 	{`(<389-400>)`, nil, `391`, []Match{[]Group{{0, 3}, {0, 3}}}},
+
+	// // Tests from https://wiki.haskell.org/Regex_Posix
+	// {`(()|.)(b)`, nil, `ab`, []Match{[]Group{{0, 2}, {0, 1}, {-1, -1}, {1, 2}}}},
+	// {`(()|[ab])(b)`, nil, `ab`, []Match{[]Group{{0, 2}, {0, 1}, {-1, -1}, {1, 2}}}},
+	// {`(()|[ab])+b`, nil, `aaab`, []Match{[]Group{{0, 4}, {2, 3}, {-1, -1}}}},
+	// {`([ab]|())+b`, nil, `aaab`, []Match{[]Group{{0, 4}, {2, 3}, {-1, -1}}}},
+	// // Bug - this should give {0,6},{3,6},{-1,-1} but it gives {0,6},{3,6},{3,3}
+	// //	{`yyyyyy`, nil, `(yyy|(x?)){2,4}`, []Match{[]Group{{0, 6}, {3, 6}, {-1, -1}}, []Group{{6, 6}, {6, 6}, {6, 6}}}},
+	// {`(a|ab|c|bcd)*(d*)`, nil, `ababcd`, []Match{[]Group{{0, 6}, {3, 6}, {6, 6}}, []Group{{6, 6}, {6, 6}, {6, 6}}}},
+	// // Bug - this should give {0,3},{0,3},{0,0},{0,3},{3,3} but it gives {0,3},{0,2},{0,1},{1,2},{2,3}
+	// //	{`((a*)(b|abc))(c*)`, nil, `abc`, []Match{[]Group{{0, 3}, {0, 3}, {0, 0}, {0, 3}, {3, 3}}}},
 }
 
-func TestFindAllMatches(t *testing.T) {
+func TestFind(t *testing.T) {
 	for _, test := range reTests {
 		t.Run(test.re+"	"+test.str, func(t *testing.T) {
 			regComp, err := Compile(test.re, test.flags...)
@@ -682,13 +699,35 @@ func TestFindAllMatches(t *testing.T) {
 					panic(fmt.Errorf("Test Error: %v", err))
 				}
 			} else {
-				matchIndices := FindAllMatches(regComp, test.str)
-				zeroGroups := make([]Group, len(matchIndices))
-				for i, m := range matchIndices {
-					zeroGroups[i] = m[0]
+				groupIndex, err := regComp.Find(test.str)
+				if err != nil { // No matches found
+					if len(test.result) == 0 {
+						return // Manually pass the test, because this is the expected behavior
+					} else {
+						t.Errorf("Wanted %v Got no matches\n", test.result)
+					}
+				} else {
+					if groupIndex != test.result[0] {
+						t.Errorf("Wanted %v	Got %v\n", test.result, groupIndex)
+					}
 				}
-				if !slices.Equal(test.result, zeroGroups) {
-					t.Errorf("Wanted %v	Got %v\n", test.result, zeroGroups)
+			}
+		})
+	}
+}
+
+func TestFindAll(t *testing.T) {
+	for _, test := range reTests {
+		t.Run(test.re+"	"+test.str, func(t *testing.T) {
+			regComp, err := Compile(test.re, test.flags...)
+			if err != nil {
+				if test.result != nil {
+					panic(fmt.Errorf("Test Error: %v", err))
+				}
+			} else {
+				matchIndices := regComp.FindAll(test.str)
+				if !slices.Equal(test.result, matchIndices) {
+					t.Errorf("Wanted %v	Got %v\n", test.result, matchIndices)
 				}
 			}
 		})
@@ -704,10 +743,10 @@ func TestFindString(t *testing.T) {
 					panic(err)
 				}
 			} else {
-				foundString := FindString(regComp, test.str)
+				foundString := regComp.FindString(test.str)
 				if len(test.result) == 0 {
 					if foundString != "" {
-						t.Errorf("Expected no match got %v\n", foundString)
+						t.Errorf("Wanted no match got %v\n", foundString)
 					}
 				} else {
 					expectedString := test.str[test.result[0].StartIdx:test.result[0].EndIdx]
@@ -720,7 +759,32 @@ func TestFindString(t *testing.T) {
 	}
 }
 
-func TestFindAllGroups(t *testing.T) {
+func TestFindAllString(t *testing.T) {
+	for _, test := range reTests {
+		t.Run(test.re+"	"+test.str, func(t *testing.T) {
+			regComp, err := Compile(test.re, test.flags...)
+			if err != nil {
+				if test.result != nil {
+					panic(err)
+				}
+			} else {
+				foundStrings := regComp.FindAllString(test.str)
+				if len(test.result) != len(foundStrings) {
+					t.Errorf("Differing number of matches: Wanted %v matches Got %v matches\n", len(test.result), len(foundStrings))
+				} else {
+					for idx, group := range test.result {
+						groupStr := test.str[group.StartIdx:group.EndIdx]
+						if groupStr != foundStrings[idx] {
+							t.Errorf("Wanted %v	Got %v\n", groupStr, foundStrings[idx])
+						}
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestFindSubmatch(t *testing.T) {
 	for _, test := range groupTests {
 		t.Run(test.re+"	"+test.str, func(t *testing.T) {
 			regComp, err := Compile(test.re, test.flags...)
@@ -729,13 +793,148 @@ func TestFindAllGroups(t *testing.T) {
 					panic(err)
 				}
 			}
-			matchIndices := FindAllMatches(regComp, test.str)
+			match, err := regComp.FindSubmatch(test.str)
+			if err != nil {
+				if len(test.result) != 0 {
+					t.Errorf("Wanted %v got no match\n", test.result[0])
+				}
+			} else if len(test.result) == 0 {
+				t.Errorf("Wanted no match got %v\n", match)
+			}
+			for i := range match {
+				if match[i].IsValid() {
+					if test.result[0][i] != match[i] {
+						t.Errorf("Wanted %v	Got %v\n", test.result[0], match)
+					}
+				} else {
+					if i < len(test.result) && test.result[0][i].IsValid() {
+						t.Errorf("Wanted %v	Got %v\n", test.result[0], match)
+					}
+				}
+			}
+		})
+	}
+}
+func TestFindStringSubmatch(t *testing.T) {
+	for _, test := range groupTests {
+		t.Run(test.re+"	"+test.str, func(t *testing.T) {
+			regComp, err := Compile(test.re, test.flags...)
+			if err != nil {
+				if test.result != nil {
+					panic(err)
+				}
+			}
+			matchStr := regComp.FindStringSubmatch(test.str)
+			if matchStr == nil {
+				if len(test.result) != 0 {
+					expectedStr := funcMap(test.result[0], func(g Group) string {
+						if g.IsValid() {
+							return test.str[g.StartIdx:g.EndIdx]
+						} else {
+							return ""
+						}
+					})
+					t.Errorf("Wanted %v got no match\n", expectedStr)
+				}
+			} else if len(test.result) == 0 {
+				t.Errorf("Wanted no match got %v\n", matchStr)
+			} else {
+				expectedStr := funcMap(test.result[0], func(g Group) string {
+					if g.IsValid() {
+						return test.str[g.StartIdx:g.EndIdx]
+					} else {
+						return ""
+					}
+				})
+				for i, groupStr := range matchStr {
+					if groupStr == "" {
+						if i < len(expectedStr) && expectedStr[i] != "" {
+							t.Errorf("Wanted %v	Got %v\n", expectedStr, matchStr)
+						}
+					} else {
+						if expectedStr[i] != groupStr {
+							t.Errorf("Wanted %v	Got %v\n", expectedStr, matchStr)
+						}
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestFindAllStringSubmatch(t *testing.T) {
+	for _, test := range groupTests {
+		t.Run(test.re+"	"+test.str, func(t *testing.T) {
+			regComp, err := Compile(test.re, test.flags...)
+			if err != nil {
+				if test.result != nil {
+					panic(err)
+				}
+			}
+			matchStrs := regComp.FindAllStringSubmatch(test.str)
+			if matchStrs == nil {
+				if len(test.result) != 0 {
+					expectedStrs := funcMap(test.result, func(m Match) []string {
+						return funcMap(m, func(g Group) string {
+							if g.IsValid() {
+								return test.str[g.StartIdx:g.EndIdx]
+							} else {
+								return ""
+							}
+						})
+					})
+					t.Errorf("Wanted %v got no match\n", expectedStrs)
+				}
+			} else if len(test.result) == 0 {
+				t.Errorf("Wanted no match got %v\n", matchStrs)
+			} else {
+				expectedStrs := funcMap(test.result, func(m Match) []string {
+					return funcMap(m, func(g Group) string {
+						if g.IsValid() {
+							return test.str[g.StartIdx:g.EndIdx]
+						} else {
+							return ""
+						}
+					})
+				})
+				for i, matchStr := range matchStrs {
+					for j, groupStr := range matchStr {
+						if groupStr == "" {
+							if j < len(expectedStrs[i]) && expectedStrs[i][j] != "" {
+								t.Errorf("Wanted %v	Got %v\n", expectedStrs, matchStrs)
+							}
+						} else {
+							if expectedStrs[i][j] != groupStr {
+								t.Errorf("Wanted %v	Got %v\n", expectedStrs, matchStrs)
+							}
+						}
+					}
+				}
+			}
+		})
+	}
+}
+
+func TestFindAllSubmatch(t *testing.T) {
+	for _, test := range groupTests {
+		t.Run(test.re+"	"+test.str, func(t *testing.T) {
+			regComp, err := Compile(test.re, test.flags...)
+			if err != nil {
+				if test.result != nil {
+					panic(err)
+				}
+			}
+			matchIndices := regComp.FindAllSubmatch(test.str)
 			for i := range matchIndices {
 				for j := range matchIndices[i] {
-					if matchIndices[i][j].isValid() {
+					if matchIndices[i][j].IsValid() {
 						if test.result[i][j] != matchIndices[i][j] {
 							t.Errorf("Wanted %v	Got %v\n", test.result, matchIndices)
 						}
+					} else {
+						if i < len(test.result) && j < len(test.result[i]) && test.result[i][j].IsValid() {
+							t.Errorf("Wanted %v	Got %v\n", test.result, matchIndices)
+						}
 					}
 				}
 			}