Added a field to State, that tells me what kind of assertion (if any) it is making. Also added function to check if a state's contents contain a given value (checks assertions), and to find all matches that a state has for a character

nfa.go

@@ -1,14 +1,69 @@
 package main
 
+import "slices"
+
 const EPSILON int = 0
 
+type assertType int
+
+const (
+	NONE assertType = iota
+	SOS
+	EOS
+	WBOUND
+	NONWBOUND
+)
+
 type State 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      []*State         // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
-	transitions map[int][]*State // 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
+	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         []*State         // The outputs of the current state ie. the 'outward arrows'. A union operator state will have more than one of these.
+	transitions    map[int][]*State // 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
+	zeroMatchFound bool             // Whether or not the state has been used for a zero-length match - only relevant for zero states
+}
+
+// Returns true if the contents of 's' contain the value at the given index of the given string
+func (s State) contentContains(str []rune, idx int) bool {
+	if s.assert == SOS {
+		return idx == 0
+	}
+	if s.assert == EOS {
+		return idx == len(str)
+	}
+	if s.assert == WBOUND {
+		if s.assert == WBOUND {
+			return isWordBoundary(str, idx)
+		}
+		if s.assert == NONWBOUND {
+			return !isWordBoundary(str, idx)
+		}
+	}
+	// Default - s.assert must be NONE
+	return slices.Contains(s.content, int(str[idx]))
+}
+
+// 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 State) matchesFor(str []rune, idx int) ([]*State, 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 == SOS && idx != 0 {
+		return make([]*State, 0), -1
+	}
+	if s.assert == EOS && idx != len(str) {
+		return make([]*State, 0), -1
+	}
+	if s.assert == WBOUND && !isWordBoundary(str, idx) {
+		return make([]*State, 0), -1
+	}
+	if s.assert == NONWBOUND && isWordBoundary(str, idx) {
+		return make([]*State, 0), -1
+	}
+	return s.transitions[int(str[idx])], len(s.transitions[int(str[idx])])
 }
 
 type NFA struct {