From ae219f763adb81f160564f8bfbc45f9b263b047a Mon Sep 17 00:00:00 2001
From: Aadhavan Srinivasan <aadhavan@twomorecents.org>
Date: Sun, 27 Oct 2024 15:30:33 -0400
Subject: [PATCH] Added alternate function, removed relevant code from main;
 also started working on escape characters

---
 main.go | 29 +++++++++++++----------------
 nfa.go  | 18 ++++++++++++++++++
 2 files changed, 31 insertions(+), 16 deletions(-)

diff --git a/main.go b/main.go
index 2cbf1e2..f4b83fc 100644
--- a/main.go
+++ b/main.go
@@ -54,7 +54,7 @@ func shuntingYard(re string) string {
 	outQueue := make([]rune, 0) // Output queue
 
 	// Actual algorithm
-	for _, c := range re_postfix {
+	for i := 0; i < len(re_postfix); i++ {
 		/* Two cases:
 		1. Current character is alphanumeric - send to output queue
 		2. Current character is operator - do the following:
@@ -65,9 +65,19 @@ func shuntingYard(re string) string {
 		3. If current character is '(', push to opStack
 		4. If current character is ')', pop from opStack (and append to outQueue) until '(' is found. Discard parantheses.
 		*/
+		c := re_postfix[i]
 		if isAlphaNum(c) {
 			outQueue = append(outQueue, c)
+			continue
 		}
+		// Escape character - NOT IMPLEMENTED YET - DO NOT USE
+		// if c == '\\' { // Escape character - next character is treated as alphanum
+		// 	if i == len(re_postfix)-1 { // End of string - panic, because backslash is an escape character (something needs to come after it)
+		// 		panic("ERROR: Backslash with no escape character.")
+		// 	}
+		// 	outQueue = append(outQueue, re_postfix[i+1])
+		// }
+
 		if isOperator(c) {
 			if len(opStack) == 0 {
 				opStack = append(opStack, c)
@@ -146,21 +156,8 @@ func thompson(re string) *State {
 		case '|':
 			s1 := mustPop(&nfa)
 			s2 := mustPop(&nfa)
-			s3 := State{}
-			s3.transitions = make(map[int][]*State)
-			s3.output = append(s3.output, s1.output...)
-			s3.output = append(s3.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.
-			s3.transitions[s1.content] = unique_append(s3.transitions[s1.content], s1)
-			s3.transitions[s2.content] = unique_append(s3.transitions[s2.content], s2)
-			s3.content = EPSILON
-			s3.isEmpty = true
-
-			nfa = append(nfa, &s3)
+			s3 := alternate(s1, s2)
+			nfa = append(nfa, s3)
 		}
 	}
 	if len(nfa) != 1 {
diff --git a/nfa.go b/nfa.go
index 2e5fd7c..4e7cba3 100644
--- a/nfa.go
+++ b/nfa.go
@@ -74,3 +74,21 @@ func kleene(s1 State) *State {
 	toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], &s1)
 	return toReturn
 }
+
+func alternate(s1 *State, s2 *State) *State {
+	toReturn := &State{}
+	toReturn.transitions = make(map[int][]*State)
+	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.
+	toReturn.transitions[s1.content] = unique_append(toReturn.transitions[s1.content], s1)
+	toReturn.transitions[s2.content] = unique_append(toReturn.transitions[s2.content], s2)
+	toReturn.content = EPSILON
+	toReturn.isEmpty = true
+
+	return toReturn
+}