diff --git a/src/regexp.rs b/src/regexp.rs
--- a/src/regexp.rs
+++ b/src/regexp.rs
@@ -97,7 +97,7 @@ impl Regexp {
 			let multistate = &index_multi[&state_hash];
 			let mut new_rules: HashMap<char, HashSet<usize>> = HashMap::new();
 
-			for key in self.rules.keys().filter(|key| multistate.contains(&key.0)) {
+			for key in self.rules.keys().filter(|(st, _c)| multistate.contains(st)) {
 				let (_st, c) = key;
 				if !new_rules.contains_key(c) {
 					new_rules.insert(*c, HashSet::new());
@@ -127,8 +127,8 @@ impl Regexp {
 		let fail = index_new.len();
 		compact_rules = compact_rules.into_iter().map(|st| if st != FAIL {st} else {fail}).collect();
 		compact_rules.extend(iter::repeat(fail).take(n));
-
-		return RegexpDFA{rules: compact_rules, end_states, alphabet_index};
+		
+		return RegexpDFA::new(compact_rules, end_states, alphabet_index);
 	}
 }
 
@@ -140,12 +140,20 @@ pub struct RegexpDFA {
 }
 
 impl RegexpDFA {
+	pub fn new(rules: Vec<usize>, end_states: HashSet<usize>, alphabet_index: HashMap<char, usize>) -> RegexpDFA {
+		if rules.len() > 0 {
+			return RegexpDFA{rules, end_states, alphabet_index};
+		} else {
+			return RegexpDFA{
+				rules: vec![1, 1],
+				end_states,
+				alphabet_index: HashMap::from([('\0', 0)])
+			};
+		}
+	}
+
 	pub fn eval(&self, s: String) -> bool {
 		let n = self.alphabet_index.len();
-		if n == 0 {
-			return s.len() == 0;
-		}
-		let fail = self.rules.len() / n;
 		let mut state = START_DFA;
 
 		for c in s.chars() {
@@ -154,27 +162,18 @@ impl RegexpDFA {
 			} else {
 				return false;
 			}
-			if state == fail {
-				return false;
-			}
 		}
 
 		return self.end_states.contains(&state);
 	}
 
 	pub fn reduce(&self) -> RegexpDFA {
-		if self.alphabet_index.len() == 0 {
-			return RegexpDFA{rules: self.rules.clone(), end_states: self.end_states.clone(), alphabet_index: self.alphabet_index.clone()};
-		}
 		let equivalents = self.find_equivalent_states();
 		return self.collapse_states(equivalents);
 	}
 
 	pub fn normalize(&self) -> RegexpDFA {
 		let n = self.alphabet_index.len();
-		if n == 0 {
-			return RegexpDFA{rules: self.rules.clone(), end_states: self.end_states.clone(), alphabet_index: self.alphabet_index.clone()}; 
-		}
 		let m = self.rules.len()/n;
 		let fail = m;
 		let mut index: Vec<usize> = vec![fail;m];