# HG changeset patch
# User Laman
# Date 2024-06-18 16:21:22
# Node ID 7e640b0cffa728e0f5af3abd3d01ca74cfe3b352
# Parent  9ddf4beb947bef7b379bf11afd0292b5773f74cd

handling unparsable patterns

diff --git a/regexp.py b/regexp.py
--- a/regexp.py
+++ b/regexp.py
@@ -1,6 +1,10 @@
 from abc import abstractmethod
 
 
+class ParsingError(Exception):
+	pass
+
+
 class Token:
 	is_skippable = False
 
@@ -111,7 +115,7 @@ def find_closing_parenthesis(pattern, k)
 		if counter == 0:
 			return k+i
 
-	return None
+	raise ParsingError(f'A closing parenthesis not found. Pattern: "{pattern}", position: {k}')
 
 
 def parse(pattern, offset=0):
@@ -126,13 +130,21 @@ def parse(pattern, offset=0):
 			res.append(inner_content)
 			i = j+1
 		elif c == "*":
-			token = res.pop()
+			try:
+				token = res.pop()
+			except IndexError as e:
+				raise ParsingError(f'The asterisk operator is missing an argument. Pattern: "{pattern}", position {i}')
 			res.append(Asterisk(token))
 			i += 1
 		elif c == "+":
-			token = res.pop()
+			try:
+				token = res.pop()
+			except IndexError as e:
+				raise ParsingError(f'The plus operator is missing an argument. Pattern: "{pattern}", position {i}')
 			res.append(Plus(token))
 			i += 1
+		elif c == ")":
+			raise ParsingError(f'An opening parenthesis not found. Pattern: "{pattern}", position: {i}')
 		else:
 			res.append(Symbol(i+offset, c))
 			i += 1
@@ -228,9 +240,14 @@ class RegexpDFA:
 
 if __name__ == "__main__":
 	tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"]
-	for pattern in ["a*b*", "a+b+", "(ab)*", "(ab)+", "a((bc)*d)*"]:
+	for pattern in ["*", "((a)", "a)"]:
 		print("#", pattern)
-		r = RegexpDFA(pattern)
+		try:
+			r = RegexpDFA(pattern)
+		except ParsingError as e:
+			print("Failed to parse the regexp:")
+			print(e)
+			continue
 		for t in tests:
 			print(t, r.match(t))
 		print()
diff --git a/src/lib.rs b/src/lib.rs
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,2 +1,2 @@
 mod regexp;
-pub use regexp::Regexp;
+pub use regexp::{Regexp, ParsingError};
diff --git a/src/main.rs b/src/main.rs
--- a/src/main.rs
+++ b/src/main.rs
@@ -2,9 +2,15 @@ use regexp::Regexp;
 
 fn main() {
 	let tests = ["", "a", "ab", "aabb", "abab", "abcd", "abcbcdbcd"];
-	for pattern in ["a*b*", "a+b+", "(ab)*", "(ab)+", "a((bc)*d)*"] {
+	for pattern in ["*", "((a)", "a)", "+a"] {
 		println!("# {pattern}");
-		let r = Regexp::new(&pattern.to_string()).determinize();
+		let r = match Regexp::new(&pattern.to_string()) {
+			Ok(r1) => r1.determinize(),
+			Err(e) => {
+				println!("{e}");
+				continue;
+			}
+		};
 		for &t in tests.iter() {
 			println!("{t} {}", r.eval(t.to_string()));
 		}
diff --git a/src/regexp.rs b/src/regexp.rs
--- a/src/regexp.rs
+++ b/src/regexp.rs
@@ -1,6 +1,7 @@
 use std::collections::{HashMap, HashSet};
 
 mod token;
+pub use token::ParsingError;
 use token::{Token, parse};
 
 const START: usize = usize::MAX;
@@ -28,14 +29,15 @@ fn decode_set(x: u64) ->HashSet<usize> {
 	return res;
 }
 
+#[derive(Debug)]
 pub struct Regexp {
 	rules: HashMap<(usize, char), HashSet<usize>>,
 	end_states: HashSet<usize>
 }
 
 impl Regexp {
-	pub fn new(pattern: &String) -> Regexp {
-		let r = parse(pattern, 0);
+	pub fn new(pattern: &String) -> Result<Regexp, ParsingError> {
+		let r = parse(pattern, 0)?;
 		let pattern_chars = Vec::from_iter(pattern.chars());
 		let mut rules: HashMap<(usize, char), HashSet<usize>> = HashMap::new();
 		
@@ -62,7 +64,7 @@ impl Regexp {
 			end_states.insert(START);
 		}
 
-		return Regexp{rules, end_states};
+		return Ok(Regexp{rules, end_states});
 	}
 
 	pub fn eval(&self, s: String) -> bool {
diff --git a/src/regexp/token.rs b/src/regexp/token.rs
--- a/src/regexp/token.rs
+++ b/src/regexp/token.rs
@@ -1,3 +1,32 @@
+use std::fmt;
+
+#[derive(Debug, Clone)]
+pub enum ParsingError {
+	Asterisk {s: String, pos: usize},
+	Plus {s: String, pos: usize},
+	OpeningParenthesis {s: String, pos: usize},
+	ClosingParenthesis {s: String, pos: usize}
+}
+
+impl fmt::Display for ParsingError {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		match self {
+			ParsingError::Asterisk {s, pos} => {
+				write!(f, "The asterisk operator is missing an argument. Pattern \"{s}\", position {pos}")
+			},
+			ParsingError::Plus {s, pos} => {
+				write!(f, "The plus operator is missing an argument. Pattern \"{s}\", position {pos}")
+			},
+			ParsingError::OpeningParenthesis {s, pos} => {
+				write!(f, "An opening parenthesis not found. Pattern \"{s}\", position {pos}")
+			},
+			ParsingError::ClosingParenthesis {s, pos} => {
+				write!(f, "An closing parenthesis not found. Pattern \"{s}\", position {pos}")
+			}
+		}
+	}
+}
+
 pub trait Token {
 	fn is_skippable(&self) -> bool {false}
 	fn list_first(&self) -> Vec<usize>;
@@ -144,7 +173,7 @@ fn find_closing_parenthesis(s: &String) 
 	return None;
 }
 
-pub fn parse(pattern: &String, offset: usize) -> Chain {
+pub fn parse(pattern: &String, offset: usize) -> Result<Chain, ParsingError> {
 	let chars: Vec<char> = pattern.chars().collect();
 	let mut res: Vec<Box<dyn Token>> = Vec::new();
 	let mut i = 0;
@@ -152,21 +181,24 @@ pub fn parse(pattern: &String, offset: u
 		let c = chars[i];
 		match c {
 			'(' => {
-				let j = find_closing_parenthesis(&pattern[i..].to_string()).unwrap() + i;
-				let inner_content = parse(&pattern[i+1..j].to_string(), offset+i+1);
+				let j = find_closing_parenthesis(&pattern[i..].to_string()).ok_or(ParsingError::ClosingParenthesis {s: pattern.clone(), pos: i})? + i;
+				let inner_content = parse(&pattern[i+1..j].to_string(), offset+i+1)?;
 				res.push(Box::new(inner_content));
 				i = j+1;
 			}
 			'*' => {
-				let token = res.pop().unwrap();
+				let token = res.pop().ok_or(ParsingError::Asterisk{s: pattern.clone(), pos: i})?;
 				res.push(Box::new(Asterisk{content: token}));
 				i += 1;
 			}
 			'+' => {
-				let token = res.pop().unwrap();
+				let token = res.pop().ok_or(ParsingError::Plus{s: pattern.clone(), pos: i})?;
 				res.push(Box::new(Plus{content: token}));
 				i += 1;
 			}
+			')' => {
+				return Err(ParsingError::OpeningParenthesis {s: pattern.clone(), pos: i});
+			}
 			c => {
 				res.push(Box::new(Symbol{position: i+offset, value: c}));
 				i += 1;
@@ -174,7 +206,7 @@ pub fn parse(pattern: &String, offset: u
 		}
 	}
 
-	return Chain{content: res};
+	return Ok(Chain{content: res});
 }
 
 mod test {
diff --git a/tests/test_regexp.rs b/tests/test_regexp.rs
--- a/tests/test_regexp.rs
+++ b/tests/test_regexp.rs
@@ -1,8 +1,9 @@
 use regexp::Regexp;
+use regexp::ParsingError;
 
 #[test]
 fn test_eval_basic_nfa() {
-	let r = Regexp::new(&String::from("abc"));
+	let r = Regexp::new(&String::from("abc")).unwrap();
 	assert!(r.eval(String::from("abc")));
 	assert!(!r.eval(String::from("ab")));
 	assert!(!r.eval(String::from("abcd")));
@@ -10,7 +11,7 @@ fn test_eval_basic_nfa() {
 
 #[test]
 fn test_eval_basic_dfa() {
-	let r = Regexp::new(&String::from("abc")).determinize();
+	let r = Regexp::new(&String::from("abc")).unwrap().determinize();
 	assert!(r.eval(String::from("abc")));
 	assert!(!r.eval(String::from("ab")));
 	assert!(!r.eval(String::from("abcd")));
@@ -18,22 +19,22 @@ fn test_eval_basic_dfa() {
 
 #[test]
 fn test_eval_empty_nfa() {
-	assert!(Regexp::new(&String::from("a*")).eval(String::from("")));
-	assert!(Regexp::new(&String::from("")).eval(String::from("")));
-	assert!(!Regexp::new(&String::from("")).eval(String::from("a")));
-	assert!(!Regexp::new(&String::from("a")).eval(String::from("")));
+	assert!(Regexp::new(&String::from("a*")).unwrap().eval(String::from("")));
+	assert!(Regexp::new(&String::from("")).unwrap().eval(String::from("")));
+	assert!(!Regexp::new(&String::from("")).unwrap().eval(String::from("a")));
+	assert!(!Regexp::new(&String::from("a")).unwrap().eval(String::from("")));
 }
 
 #[test]
 fn test_eval_empty_dfa() {
-	assert!(Regexp::new(&String::from("a*")).determinize().eval(String::from("")));
-	assert!(Regexp::new(&String::from("")).determinize().eval(String::from("")));
-	assert!(!Regexp::new(&String::from("")).determinize().eval(String::from("a")));
+	assert!(Regexp::new(&String::from("a*")).unwrap().determinize().eval(String::from("")));
+	assert!(Regexp::new(&String::from("")).unwrap().determinize().eval(String::from("")));
+	assert!(!Regexp::new(&String::from("")).unwrap().determinize().eval(String::from("a")));
 }
 
 #[test]
 fn test_eval_asterisk_nfa() {
-	let r = Regexp::new(&String::from("a*b*"));
+	let r = Regexp::new(&String::from("a*b*")).unwrap();
 	assert!(r.eval(String::from("a")));
 	assert!(r.eval(String::from("ab")));
 	assert!(r.eval(String::from("aabb")));
@@ -42,7 +43,7 @@ fn test_eval_asterisk_nfa() {
 
 #[test]
 fn test_eval_asterisk_dfa() {
-	let r = Regexp::new(&String::from("a*b*")).determinize();
+	let r = Regexp::new(&String::from("a*b*")).unwrap().determinize();
 	assert!(r.eval(String::from("a")));
 	assert!(r.eval(String::from("ab")));
 	assert!(r.eval(String::from("aabb")));
@@ -51,7 +52,7 @@ fn test_eval_asterisk_dfa() {
 
 #[test]
 fn test_eval_plus_nfa() {
-	let r = Regexp::new(&String::from("(ab)+"));
+	let r = Regexp::new(&String::from("(ab)+")).unwrap();
 	assert!(!r.eval(String::from("a")));
 	assert!(r.eval(String::from("ab")));
 	assert!(r.eval(String::from("abab")));
@@ -60,9 +61,33 @@ fn test_eval_plus_nfa() {
 
 #[test]
 fn test_eval_plus_dfa() {
-	let r = Regexp::new(&String::from("(ab)+")).determinize();
+	let r = Regexp::new(&String::from("(ab)+")).unwrap().determinize();
 	assert!(!r.eval(String::from("a")));
 	assert!(r.eval(String::from("ab")));
 	assert!(r.eval(String::from("abab")));
 	assert!(!r.eval(String::from("aabb")));
 }
+
+#[test]
+fn test_invalid_asterisk() {
+	let x = Regexp::new(&String::from("*"));
+	assert!(matches!(x, Err(ParsingError::Asterisk{s: _, pos: 0})));
+}
+
+#[test]
+fn test_invalid_plus() {
+	let x = Regexp::new(&String::from("+"));
+	assert!(matches!(x, Err(ParsingError::Plus{s: _, pos: 0})));
+}
+
+#[test]
+fn test_invalid_closing_parenthesis() {
+	let x = Regexp::new(&String::from("(a"));
+	assert!(matches!(x, Err(ParsingError::ClosingParenthesis{s: _, pos: 0})));
+}
+
+#[test]
+fn test_invalid_opening_parenthesis() {
+	let x = Regexp::new(&String::from("a)"));
+	assert!(matches!(x, Err(ParsingError::OpeningParenthesis{s: _, pos: 1})));
+}