Changed \Z to \z to fit with Go's naming

LICENSE

@@ -0,0 +1,11 @@
+The MIT License (MIT)
+
+Copyright (c) 2025 Aadhavan Srinivasan
+
+All rights reserved.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Makefile

@@ -1,9 +1,13 @@
-.DEFAULT_GOAL := build
+.DEFAULT_GOAL := buildCmd
-.PHONY: fmt vet build
+.PHONY: fmt vet buildLib buildCmd test
 
 fmt:
 	go fmt ./...
 vet: fmt
 	go vet ./...
-build: vet
+buildLib: vet
 	go build -gcflags="-N -l" ./...
+buildCmd: buildLib
+	go build -C cmd/ -o re ./...
+test: buildCmd
+	go test -v ./...

regex/compile.go

@@ -407,7 +407,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 			} else {
 				escapedNode, err := newEscapedNode(re_postfix[i], false)
 				if err != nil {
-					return nil, fmt.Errorf("invalid escape character in expression")
+					return nil, err
 				}
 				outQueue = append(outQueue, escapedNode)
 			}
@@ -575,7 +575,7 @@ func shuntingYard(re string, flags ...ReFlag) ([]postfixNode, error) {
 					} else {
 						escapedNode, err := newEscapedNode(re_postfix[i], true)
 						if err != nil {
-							return nil, fmt.Errorf("invalid escape character in character class")
+							return nil, err
 						}
 						chars = append(chars, escapedNode)
 						i++
@@ -878,6 +878,10 @@ func thompson(re []postfixNode) (Reg, error) {
 						stateToAdd.assert = wboundAssert
 					case 'B':
 						stateToAdd.assert = nonwboundAssert
+					case 'A':
+						stateToAdd.assert = soiAssert
+					case 'z':
+						stateToAdd.assert = eoiAssert
 					}
 				} else { // Lookaround
 					stateToAdd.lookaroundRegex = string(c.contents)

regex/doc.go

@@ -0,0 +1,7 @@
+/*
+Package regex implements an NFA-based engine to search for
+regular expressions in strings. The engine does not use backtracking,
+and is therefore not vulnerable to catastrophic backtracking. The regex
+syntax supported (a variation of Golang's) is specified in the Syntax section.
+*/
+package regex

regex/nfa.go

@@ -11,8 +11,10 @@ type assertType int
 
 const (
 	noneAssert assertType = iota
-	sosAssert
+	sosAssert             // Start of string (^)
-	eosAssert
+	soiAssert             // Start of input (\A)
+	eosAssert             // End of string ($)
+	eoiAssert             // End of input (\Z)
 	wboundAssert
 	nonwboundAssert
 	plaAssert        // Positive lookahead
@@ -119,6 +121,15 @@ func (s nfaState) checkAssertion(str []rune, idx int) bool {
 		// Index is at the end of the string, or it points to the last character which is a newline
 		return idx == len(str) || (multilineMode && str[idx] == '\n')
 	}
+	if s.assert == soiAssert {
+		// Only true at the start of the input, regardless of mode
+		return idx == 0
+	}
+	if s.assert == eoiAssert {
+		// Only true at the end of the input, regardless of mode
+		return idx == len(str)
+	}
+
 	if s.assert == wboundAssert {
 		return isWordBoundary(str, idx)
 	}

regex/postfixNode.go

@@ -95,6 +95,16 @@ func newEscapedNode(c rune, inCharClass bool) (postfixNode, error) {
 			toReturn.nodetype = assertionNode
 			toReturn.contents = append(toReturn.contents, c)
 		}
+		if c == 'B' && inCharClass { // Invalid
+			return postfixNode{}, fmt.Errorf("word boundaries are not allowed in character class")
+		}
+	case 'A', 'z': // A is start of input, z is end of input (regardless of RE_MULTILINE)
+		if inCharClass {
+			return postfixNode{}, fmt.Errorf("input boundaries are not allowed in character class")
+		} else {
+			toReturn.nodetype = assertionNode
+			toReturn.contents = append(toReturn.contents, c)
+		}
 	case 'n': // Newline character
 		toReturn.nodetype = characterNode
 		toReturn.contents = append(toReturn.contents, '\n')

regex/re_test.go

@@ -443,8 +443,11 @@ var reTests = []struct {
 	{`abc$`, []ReFlag{RE_MULTILINE}, "jkl\n123abc\nxyz", []Group{{7, 10}}},
 	{`^`, nil, "jkl\n123abc\nxyz", []Group{{0, 0}}},
 	{`^`, []ReFlag{RE_MULTILINE}, "jkl\n123abc\nxyz", []Group{{0, 0}, {4, 4}, {11, 11}}},
+	{`\A`, []ReFlag{RE_MULTILINE}, "jkl\n123abc\nxyz", []Group{{0, 0}}},
 	{`$`, nil, "jkl\n123abc\nxyz", []Group{{14, 14}}},
 	{`$`, []ReFlag{RE_MULTILINE}, "jkl\n123abc\nxyz", []Group{{3, 3}, {10, 10}, {14, 14}}},
+	{`\z`, []ReFlag{RE_MULTILINE}, "jkl\n123abc\nxyz", []Group{{14, 14}}},
+	{`^abc\z`, []ReFlag{RE_MULTILINE}, "abc\nabc\nabc", []Group{{8, 11}}},
 
 	{`a.b`, nil, "a\nb", []Group{}},
 	{`a.b`, []ReFlag{RE_SINGLE_LINE}, "a\nb", []Group{{0, 3}}},