From 8dbecde3aeea37e7eae201395275108e3fc99e47 Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Thu, 31 Oct 2024 16:51:53 -0400
Subject: [PATCH] Added support for detecting assertion characters; changed
 input so that newline isn't required

---
 main.go | 28 +++++++++++++++++++++++++---
 1 file changed, 25 insertions(+), 3 deletions(-)

diff --git a/main.go b/main.go
index 1c05625..b0a9409 100644
--- a/main.go
+++ b/main.go
@@ -3,6 +3,7 @@ package main
 import (
 	"bufio"
 	"fmt"
+	"io"
 	"os"
 	"slices"
 
@@ -128,6 +129,13 @@ func shuntingYard(re string) []postfixNode {
 			outQueue = append(outQueue, newPostfixNode(dotChars()...))
 			continue
 		}
+		if c == '^' { // Start-of-string assertion
+			outQueue = append(outQueue, newPostfixNode(c))
+		}
+		if c == '$' { // End-of-string assertion
+			outQueue = append(outQueue, newPostfixNode(c))
+		}
+
 		if isOperator(c) {
 			if len(opStack) == 0 {
 				opStack = append(opStack, c)
@@ -195,13 +203,27 @@ func shuntingYard(re string) []postfixNode {
 func thompson(re []postfixNode) *State {
 	nfa := make([]*State, 0) // Stack of states
 	for _, c := range re {
-		if c.nodetype == CHARACTER {
+		if c.nodetype == CHARACTER || c.nodetype == ASSERTION {
 			state := State{}
 			state.transitions = make(map[int][]*State)
 			state.content = rune2Contents(c.contents)
 			state.output = make([]*State, 0)
 			state.output = append(state.output, &state)
 			state.isEmpty = false
+			if c.nodetype == ASSERTION {
+				state.content = newContents(EPSILON) // Ideally, an assertion shouldn't have any content, since it doesn't say anything about the content of string
+				state.isEmpty = true
+				switch c.contents[0] {
+				case '^':
+					state.assert = SOS
+				case '$':
+					state.assert = EOS
+				case 'b':
+					state.assert = WBOUND
+				case 'B':
+					state.assert = NONWBOUND
+				}
+			}
 			nfa = append(nfa, &state)
 		}
 		// Must be an operator if it isn't a character
@@ -262,14 +284,14 @@ func main() {
 	// Read test string from stdin
 	reader := bufio.NewReader(os.Stdin)
 	test_str, err := reader.ReadString('\n')
-	if err != nil {
+	if err != nil && err != io.EOF {
 		panic(err)
 	}
 	fmt.Scanln(&test_str)
 	re_postfix := shuntingYard(re)
-	// fmt.Println(re_postfix)
 	startState := thompson(re_postfix)
 	matchIndices := findAllMatches(startState, test_str)
+
 	inColor := false
 	if len(matchIndices) > 0 {
 		for i, c := range test_str {