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 {