Created function that returns a 'default' state

I added support for hex values (eg. \x0F), octal values (eg. \012) and
extended hex values (eg. \x{000F2A}). I also expanded the abilities of
character clsses, to include things like escaped characters (eg. [aefp\)])
and character ranges _inside_ inverted character classes (eg. [^\w] which is
functionally equivalent to [\W]).

compile.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"fmt"
+	"math"
 	"slices"
 	"strconv"
 	"unicode"
@@ -184,6 +185,40 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			re_postfix = append(re_postfix, NONCAPLPAREN_CHAR)
 			i += 3
 		}
+		if i < len(re_runes) && re_runes[i] == '\\' { // Something is being escaped (I don't add the backslash to re_postfix, because it was already added earlier)
+			i++
+			if i >= len(re_runes) {
+				return nil, fmt.Errorf("Stray backslash in expression.")
+			}
+			if re_runes[i] == 'x' {
+				re_postfix = append(re_postfix, re_runes[i])
+				i++
+				if i >= len(re_runes) {
+					return nil, fmt.Errorf("Stray backslash in expression.")
+				}
+				if re_runes[i] == '{' {
+					re_postfix = append(re_postfix, re_runes[i:i+8]...)
+					i += 7
+					if i >= len(re_runes) {
+						return nil, fmt.Errorf("Stray backslash in expression.")
+					}
+				} else if isHex(re_runes[i]) {
+					re_postfix = append(re_postfix, re_runes[i:i+2]...)
+					i += 2
+				} else {
+					return nil, fmt.Errorf("Invalid hex value in expression.")
+				}
+			} else if isOctal(re_runes[i]) {
+				numDigits := 1
+				for i+numDigits < len(re_runes) && numDigits < 3 && isOctal(re_runes[i+numDigits]) { // Skip while we see an octal character (max of 3)
+					numDigits++
+				}
+				re_postfix = append(re_postfix, re_runes[i:i+numDigits]...)
+				i += (numDigits - 1) // I have to move back a step, so that I can add a concatenation operator if necessary, and so that the increment at the bottom of the loop works as intended
+			} else {
+				re_postfix = append(re_postfix, re_runes[i])
+			}
+		}
 		if i < len(re_runes) && re_runes[i] == '(' && (i == 0 || re_runes[i-1] != '\\') && (i < len(re_runes)-2 && re_runes[i+1] == '?' && slices.Contains([]rune{'=', '!', '<'}, re_runes[i+2])) { // Unescaped open parentheses followed by question mark then '<', '!' or '=' => lokaround. Don't mess with it.
 			i++ // Step inside
 			if i == len(re_runes)-1 || (re_runes[i+1] != '=' && re_runes[i+1] != '!' && re_runes[i+1] != '<') {
@@ -253,7 +288,45 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 				return nil, fmt.Errorf("ERROR: Backslash with no escape character.")
 			}
 			i++
+			if re_postfix[i] == 'x' { // Hex value
+				i++
+				if re_postfix[i] == '{' && i < len(re_postfix)-6 { // Expanded hex code
+					var hexVal int
+					n, err := fmt.Sscanf(string(re_postfix[i:]), "{%x}", &hexVal)
+					if n < 1 || err != nil {
+						return nil, fmt.Errorf("Error parsing expanded hex code in expression.")
+					}
+					outQueue = append(outQueue, newPostfixCharNode(rune(hexVal)))
+					i += 7
+				} else if i < len(re_postfix)-1 { // Two-digit hex code
+					hexVal, err := strconv.ParseInt(string([]rune{re_postfix[i], re_postfix[i+1]}), 16, 64) // Convert the two hex values into a rune slice, then to a string. Parse the string into an int with strconv.ParseInt()
+					if err != nil {
+						return nil, fmt.Errorf("Error parsing hex characters in expression.")
+					}
+					i += 2
+					outQueue = append(outQueue, newPostfixCharNode(rune(hexVal)))
+				} else {
+					return nil, fmt.Errorf("Not enough hex characters found in expression.")
+				}
+			} else if isOctal(re_postfix[i]) { // Octal value
+				var octVal int
+				n, err := fmt.Sscanf(string(re_postfix[i:]), "%d", &octVal)
+				if n < 1 || err != nil {
+					return nil, fmt.Errorf("Error parsing octal value in expression.")
+				}
+				if octVal > 777 {
+					return nil, fmt.Errorf("Invalid octal value in expression.")
+				}
+				i += int(math.Ceil(math.Log10(float64(octVal)))) // Shift forward by the number of digits that were parsed
+				i--                                              // Move back one character, because the loop increment will move us back to the next character automatically
+				octValBase10, err := strconv.ParseInt(strconv.Itoa(octVal), 8, 0)
+				if err != nil {
+					return nil, fmt.Errorf("Error parsing octal value in expression.")
+				}
+				outQueue = append(outQueue, newPostfixCharNode(rune(octValBase10)))
+			} else {
 				outQueue = append(outQueue, newEscapedNode(re_postfix[i]))
+			}
 			continue // Escaped character will automatically be skipped when loop variable increments
 		}
 
@@ -342,25 +415,60 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 				invertMatch = true
 				i++
 			}
-			chars := make([]rune, 0) // List of characters -  used only for character classes
+			chars := make([]postfixNode, 0) // List of nodes - used only for character classes
 			for i < len(re_postfix) {
 				if re_postfix[i] == RBRACKET {
 					break
 				}
-				chars = append(chars, re_postfix[i])
+				if re_postfix[i] == '\\' { // Backslash indicates a character to be escaped
+					if i == len(re_postfix)-1 {
+						return nil, fmt.Errorf("Stray backslash in character class.")
+					}
+					i++ // Step past backslash
+
+					if re_postfix[i] == 'x' { // Hex value
 						i++
+						if re_postfix[i] == '{' && i < len(re_postfix)-7 { // Expanded hex code
+							var hexVal int
+							n, err := fmt.Sscanf(string(re_postfix[i:]), "{%x}", &hexVal)
+							if n < 1 || err != nil {
+								return nil, fmt.Errorf("Error parsing expanded hex code in character class.")
+							}
+							chars = append(chars, newPostfixCharNode(rune(hexVal)))
+							i += 8
+						} else if i < len(re_postfix)-2 { // Two-digit hex code
+							hexVal, err := strconv.ParseInt(string([]rune{re_postfix[i], re_postfix[i+1]}), 16, 64) // Convert the two hex values into a rune slice, then to a string. Parse the string into an int with strconv.ParseInt()
+							if err != nil {
+								return nil, fmt.Errorf("Error parsing hex characters in character class.")
+							}
+							i += 2
+							chars = append(chars, newPostfixCharNode(rune(hexVal)))
+						} else {
+							return nil, fmt.Errorf("Not enough hex characters found in character class.")
+						}
+					} else if unicode.IsDigit(re_postfix[i]) { // Octal value
+						var octVal int
+						n, err := fmt.Sscanf(string(re_postfix[i:]), "%d", &octVal)
+						if n < 1 || err != nil {
+							return nil, fmt.Errorf("Error parsing octal value in character class.")
+						}
+						if octVal > 0777 {
+							return nil, fmt.Errorf("Invalid octal value in character class.")
+						}
+						i += int(math.Ceil(math.Log10(float64(octVal)) / math.Log10(8))) // Shift forward by the number of digits that were parsed
+						chars = append(chars, newPostfixCharNode(rune(octVal)))
+					} else {
+						chars = append(chars, newEscapedNode(re_postfix[i]))
+					}
+				} else {
+					chars = append(chars, newPostfixCharNode(re_postfix[i]))
+					i++
+				}
 			}
 			if i == len(re_postfix) { // We have reached the end of the string, so we didn't encounter a closing brakcet. Panic.
 				return nil, fmt.Errorf("Opening bracket without closing bracket.")
 			}
-			if !invertMatch {
+			outQueue = append(outQueue, newCharClassNode(chars, invertMatch))
-				outQueue = append(outQueue, newPostfixCharNode(chars...))
-			} else {
-				// Invert match - create an allChars postfixNode, then add the given states to its 'except' list.
-				toAdd := newPostfixDotNode()
-				toAdd.except = chars
-				outQueue = append(outQueue, toAdd)
-			}
 			continue
 		}
 		if c == '{' {
@@ -476,10 +584,29 @@ func thompson(re []postfixNode) (Reg, error) {
 			if c.allChars {
 				state.allChars = true
 				if len(c.except) != 0 {
-					state.except = append([]rune{}, c.except...)
+					// For each node that I am 'excepting' (eg. in an inverted character class):
+					// 		- If the node itself has exceptions, then the exceptions cancel out.
+					// 		Eg. [^\w] == [\W]
+					// 		- Since an allChars node is the only kind that _can_ have exceptions, that's what I check for.
+					//		- If the node doesn't have exceptions (allChars == false) then the contents of the node are added to the except list.
+					for _, node := range c.except {
+						if node.allChars {
+							// For each postfixNode in node.except, extract the contents of the postfixNode. Concatenate them all,
+							// and them to the state's _content_. As mentioned above, if the exception has exceptions, then we can match
+							// those.
+							nodeExceptChars := slices.Concat(Map(node.except, func(node postfixNode) []rune {
+								return node.contents
+							})...)
+							state.content = rune2Contents(nodeExceptChars)
+						} else {
+							state.except = append(state.except, node.contents...)
 						}
 					}
-			state.content = rune2Contents(c.contents)
+				}
+			}
+			// Convert the current contents to []int, convert the result of rune2contents to []int, append then
+			// convert back to stateContents.
+			state.content = stateContents(append([]int(state.content), []int(rune2Contents(c.contents))...))
 			state.output = make([]*State, 0)
 			state.output = append(state.output, &state)
 			state.isEmpty = false
@@ -561,6 +688,19 @@ func thompson(re []postfixNode) (Reg, error) {
 
 			}
 		}
+		if c.nodetype == CHARCLASS { // 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 := Map(c.nodeContents, func(node postfixNode) *State {
+				s := newState()
+				s.content = rune2Contents(node.contents)
+				return &s
+			})
+			// Reduce the list of states down to a single state by alternating them
+			toAdd := Reduce(states, func(s1 *State, s2 *State) *State {
+				return alternate(s1, s2)
+			})
+			nfa = append(nfa, toAdd)
+		}
 		// Must be an operator if it isn't a character
 		switch c.nodetype {
 		case CONCATENATE:
@@ -613,7 +753,7 @@ func thompson(re []postfixNode) (Reg, error) {
 				stateToAdd = concatenate(stateToAdd, s2)
 			} else { // Case 2
 				for i := c.startReps; i < c.endReps; i++ {
-					stateToAdd = concatenate(stateToAdd, question(state))
+					stateToAdd = concatenate(stateToAdd, question(cloneState(state)))
 				}
 			}
 			nfa = append(nfa, stateToAdd)

main.go

@@ -119,12 +119,12 @@ func main() {
 		}
 		matchIndices := make([]Match, 0)
 		if matchNumFlagEnabled {
-			tmp, err := findNthMatch(regComp, test_str, *matchNum)
+			tmp, err := FindNthMatch(regComp, test_str, *matchNum)
 			if err == nil {
 				matchIndices = append(matchIndices, tmp)
 			}
 		} else {
-			matchIndices = findAllMatches(regComp, test_str)
+			matchIndices = FindAllMatches(regComp, test_str)
 		}
 
 		if *printMatchesFlag {

matching.go

@@ -138,10 +138,29 @@ func pruneIndices(indices []Match) []Match {
 	return toRet
 }
 
-// findNthMatch finds the 'n'th match of the regex represented by the given start-state, with
+// 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:
+//  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)
+	if err != nil {
+		return ""
+	}
+	return str[match[0].startIdx:match[0].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 {
+//
+//}
+
+// FindNthMatch finds the 'n'th match of the regex represented by the given start-state, with
 // 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 FindNthMatch(regex Reg, str string, n int) (Match, error) {
 	idx := 0
 	matchNum := 0
 	str_runes := []rune(str)
@@ -160,9 +179,9 @@ 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
+// 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 {
+func FindAllMatches(regex Reg, str string) []Match {
 	idx := 0
 	str_runes := []rune(str)
 	var matchFound bool
@@ -180,7 +199,7 @@ func findAllMatches(regex Reg, str string) []Match {
 	return indices
 }
 
-// Helper for findAllMatches. Returns whether it found a match, the
+// 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.
 //

misc.go

@@ -131,3 +131,11 @@ func expandSlice[T any](slc []T, newSize int) []T {
 	copy(toRet, slc)
 	return toRet
 }
+
+func isHex(c rune) bool {
+	return slices.Contains([]rune("0123456789abcdefABCDEF"), c)
+}
+
+func isOctal(c rune) bool {
+	return slices.Contains([]rune("01234567"), c)
+}

nfa.go

@@ -136,7 +136,7 @@ func (s State) checkAssertion(str []rune, idx int) bool {
 			strToMatch = string(runesToMatch)
 		}
 
-		matchIndices := findAllMatches(Reg{startState, s.lookaroundNumCaptureGroups}, strToMatch)
+		matchIndices := FindAllMatches(Reg{startState, s.lookaroundNumCaptureGroups}, strToMatch)
 
 		numMatchesFound := 0
 		for _, matchIdx := range matchIndices {
@@ -314,3 +314,18 @@ func question(s1 *State) *State { // Use the fact that ab? == a(b|)
 	s3 := alternate(s1, s2)
 	return s3
 }
+
+// Creates and returns a new state with the 'default' values.
+func newState() State {
+	ret := State{
+		output:          make([]*State, 0),
+		transitions:     make(map[int][]*State),
+		assert:          NONE,
+		except:          append([]rune{}, 0),
+		lookaroundRegex: "",
+		groupEnd:        false,
+		groupBegin:      false,
+	}
+	ret.output = append(ret.output, &ret)
+	return ret
+}

postfixNode.go

@@ -2,9 +2,14 @@ package main
 
 type NodeType int
 
+// This is a slice containing all escapable characters that have special meaning.
+// Eg. \b is word boundary, \w is word character etc.
+var escapedChars []rune = []rune("wWdDbBnaftrvsS0")
+
 // This is a list of the possible node types
 const (
 	CHARACTER NodeType = iota
+	CHARCLASS
 	PIPE
 	CONCATENATE
 	KLEENE
@@ -29,9 +34,31 @@ type postfixNode struct {
 	startReps      int           // Minimum number of times the node should be repeated - used with numeric specifiers
 	endReps        int           // Maximum number of times the node should be repeated - used with numeric specifiers
 	allChars       bool          // Whether or not the current node represents all characters (eg. dot metacharacter)
-	except         []rune // For inverted character classes, we match every unicode character _except_ a few. In this case, allChars is true and the exceptions are placed here.
+	except         []postfixNode // For inverted character classes, we match every unicode character _except_ a few. In this case, allChars is true and the exceptions are placed here.
 	lookaroundSign int           // ONLY USED WHEN nodetype == ASSERTION. Whether we have a positive or negative lookaround.
 	lookaroundDir  int           // Lookbehind or lookahead
+	nodeContents   []postfixNode // ONLY USED WHEN nodetype == CHARCLASS. Holds all the nodes inside the given CHARCLASS node.
+}
+
+// Converts the given list of postfixNodes to one node of type CHARCLASS.
+// Used to convert eg. 'a', 'b' and 'c' to '[abc]'.
+// If the character class is negated, it returns a postfixNode of type CHARACTER.
+// This node will behave like the dot metacharacter, but it has a longer list of runes that
+// it will not match.
+func newCharClassNode(nodes []postfixNode, negated bool) postfixNode {
+	rtv := postfixNode{}
+	rtv.nodetype = CHARCLASS
+	rtv.startReps = 1
+	rtv.endReps = 1
+	if negated {
+		rtv.nodetype = CHARACTER
+		rtv.contents = []rune{ANY_CHAR}
+		rtv.allChars = true
+		rtv.except = nodes
+	} else {
+		rtv.nodeContents = nodes
+	}
+	return rtv
 }
 
 // Creates a new escaped node - the given character is assumed to have been preceded by a backslash
@@ -45,25 +72,43 @@ func newEscapedNode(c rune) postfixNode {
 		toReturn.contents = append(toReturn.contents, whitespaceChars...)
 	case 'S': // Non-whitespace
 		toReturn = newPostfixDotNode()
-		toReturn.except = append([]rune{}, whitespaceChars...)
+		toReturn.except = append([]postfixNode{}, newPostfixNode(whitespaceChars...))
 	case 'd': // Digits
 		toReturn.nodetype = CHARACTER
 		toReturn.contents = append(toReturn.contents, digitChars...)
 	case 'D': // Non-digits
 		toReturn = newPostfixDotNode()
-		toReturn.except = append([]rune{}, digitChars...)
+		toReturn.except = append([]postfixNode{}, newPostfixNode(digitChars...))
 	case 'w': // word character
 		toReturn.nodetype = CHARACTER
 		toReturn.contents = append(toReturn.contents, wordChars...)
 	case 'W': // Non-word character
 		toReturn = newPostfixDotNode()
-		toReturn.except = append([]rune{}, wordChars...)
+		toReturn.except = append([]postfixNode{}, newPostfixNode(wordChars...))
 	case 'b', 'B':
 		toReturn.nodetype = ASSERTION
 		toReturn.contents = append(toReturn.contents, c)
 	case 'n': // Newline character
 		toReturn.nodetype = CHARACTER
 		toReturn.contents = append(toReturn.contents, '\n')
+	case '0': // NULL character
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(0))
+	case 'a': // Bell character
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(7))
+	case 'f': // Form feed character
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(12))
+	case 't': // Horizontal tab character
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(9))
+	case 'r': // Carriage return
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(13))
+	case 'v': // Vertical tab
+		toReturn.nodetype = CHARACTER
+		toReturn.contents = append(toReturn.contents, rune(11))
 	default: // None of the above - append it as a regular character
 		toReturn.nodetype = CHARACTER
 		toReturn.contents = append(toReturn.contents, c)

re_test.go

@@ -148,6 +148,7 @@ var reTests = []struct {
 	{"^((3[7-9])|([4-9][0-9])|([1-9][0-9][0-9])|(1000))$", "040", []Group{}},
 	{"^((3[7-9])|([4-9][0-9])|([1-9][0-9][0-9])|(1000))$", "400", []Group{{0, 3}}},
 	{"^((3[7-9])|([4-9][0-9])|([1-9][0-9][0-9])|(1000))$", "4000", []Group{}},
+	{"a{1,3}", "aaaaa", []Group{{0, 3}, {3, 5}}},
 
 	// Lookaround tests
 	{"(?<=bo)y", "boy", []Group{{2, 3}}},
@@ -191,7 +192,7 @@ func TestFindAllMatches(t *testing.T) {
 			if err != nil {
 				panic(err)
 			}
-			matchIndices := findAllMatches(regComp, test.str)
+			matchIndices := FindAllMatches(regComp, test.str)
 			zeroGroups := make([]Group, len(matchIndices))
 			for i, m := range matchIndices {
 				zeroGroups[i] = m[0]
@@ -210,7 +211,7 @@ func TestFindAllGroups(t *testing.T) {
 			if err != nil {
 				panic(err)
 			}
-			matchIndices := findAllMatches(regComp, test.str)
+			matchIndices := FindAllMatches(regComp, test.str)
 			for i := range matchIndices {
 				for j := range matchIndices[i] {
 					if matchIndices[i][j].isValid() {