diff --git a/src/error/mod.rs b/src/error/mod.rs
index 7f3e133..9e6933a 100644
--- a/src/error/mod.rs
+++ b/src/error/mod.rs
@@ -29,6 +29,12 @@ pub enum Error {
 
     /// A value has the wrong type.
     TypeError,
+
+    /// An opening brace without a matching closing brace was found.
+    UnmatchedLBrace,
+
+    /// A closing brace without a matching opening brace was found.
+    UnmatchedRBrace,
 }
 
 impl Error {
diff --git a/src/lib.rs b/src/lib.rs
index dfb3c62..d0166ee 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -25,6 +25,9 @@ mod test {
         assert_eq!(eval("true"), Ok(Value::Boolean(true)));
         assert_eq!(eval("false"), Ok(Value::Boolean(false)));
         assert_eq!(eval("blub"), Err(Error::IdentifierNotFound));
+        assert_eq!(eval("-3"), Ok(Value::Int(-3)));
+        assert_eq!(eval("-3.6"), Ok(Value::Float(-3.6)));
+        assert_eq!(eval("----3"), Ok(Value::Int(3)));
     }
 
     #[test]
@@ -41,6 +44,14 @@ mod test {
         assert_eq!(eval("5-3.0"), Ok(Value::Float(2.0)));
         assert_eq!(eval("5 / 4.0"), Ok(Value::Float(1.25)));
         assert_eq!(eval("5.0 *3"), Ok(Value::Float(15.0)));
+        assert_eq!(eval("5.0 *-3"), Ok(Value::Float(-15.0)));
+        assert_eq!(eval("5.0 *- 3"), Ok(Value::Float(-15.0)));
+        assert_eq!(eval("5.0 * -3"), Ok(Value::Float(-15.0)));
+        assert_eq!(eval("5.0 * - 3"), Ok(Value::Float(-15.0)));
+        assert_eq!(eval("-5.0 *-3"), Ok(Value::Float(15.0)));
+        assert_eq!(eval("3+-1"), Ok(Value::Int(2)));
+        assert_eq!(eval("-3-5"), Ok(Value::Int(-8)));
+        assert_eq!(eval("-5--3"), Ok(Value::Int(-2)));
     }
 
     #[test]
@@ -52,6 +63,36 @@ mod test {
         assert_eq!(eval("5 / 4*2"), Ok(Value::Int(2)));
         assert_eq!(eval("1-5 *3/15"), Ok(Value::Int(0)));
         assert_eq!(eval("15/7/2.0"), Ok(Value::Float(1.0)));
-        assert_eq!(eval("15.0/7/2"), Ok(Value::Float(15.0/7.0/2.0)));
+        assert_eq!(eval("15.0/7/2"), Ok(Value::Float(15.0 / 7.0 / 2.0)));
+        assert_eq!(eval("15.0/-7/2"), Ok(Value::Float(15.0 / -7.0 / 2.0)));
+        assert_eq!(eval("-15.0/7/2"), Ok(Value::Float(-15.0 / 7.0 / 2.0)));
+        assert_eq!(eval("-15.0/7/-2"), Ok(Value::Float(-15.0 / 7.0 / -2.0)));
     }
+
+    #[test]
+    fn test_braced_examples() {
+        assert_eq!(eval("(1)"), Ok(Value::Int(1)));
+        assert_eq!(eval("( 1.0 )"), Ok(Value::Float(1.0)));
+        assert_eq!(eval("( true)"), Ok(Value::Boolean(true)));
+        assert_eq!(eval("( -1 )"), Ok(Value::Int(-1)));
+        assert_eq!(eval("-(1)"), Ok(Value::Int(-1)));
+        assert_eq!(eval("-(1 + 3) * 7"), Ok(Value::Int(-28)));
+        assert_eq!(eval("(1 * 1) - 3"), Ok(Value::Int(-2)));
+        assert_eq!(eval("4 / (2 * 2)"), Ok(Value::Int(1)));
+        assert_eq!(eval("7/(7/(7/(7/(7/(7)))))"), Ok(Value::Int(1)));
+    }
+
+    #[test]
+    fn test_type_errors() {
+        assert_eq!(
+            eval("-true"),
+            Err(Error::expected_number(Value::Boolean(true)))
+        );
+        assert_eq!(
+            eval("1-true"),
+            Err(Error::expected_number(Value::Boolean(true)))
+        );
+        assert_eq!(eval("true-"), Err(Error::wrong_argument_amount(1, 2)));
+    }
+
 }
diff --git a/src/operator/mod.rs b/src/operator/mod.rs
index 2f60237..350c153 100644
--- a/src/operator/mod.rs
+++ b/src/operator/mod.rs
@@ -23,8 +23,10 @@ pub trait Operator {
 pub struct RootNode;
 pub struct Add;
 pub struct Sub;
+pub struct Neg;
 pub struct Mul;
 pub struct Div;
+pub struct Braced;
 
 pub struct Const {
     value: Value,
@@ -75,9 +77,13 @@ impl Operator for Add {
         expect_number(&arguments[1])?;
 
         if arguments[0].is_int() && arguments[1].is_int() {
-            Ok(Value::Int(arguments[0].as_int().unwrap() + arguments[1].as_int().unwrap()))
+            Ok(Value::Int(
+                arguments[0].as_int().unwrap() + arguments[1].as_int().unwrap(),
+            ))
         } else {
-            Ok(Value::Float(arguments[0].as_float().unwrap() + arguments[1].as_float().unwrap()))
+            Ok(Value::Float(
+                arguments[0].as_float().unwrap() + arguments[1].as_float().unwrap(),
+            ))
         }
     }
 }
@@ -97,9 +103,34 @@ impl Operator for Sub {
         expect_number(&arguments[1])?;
 
         if arguments[0].is_int() && arguments[1].is_int() {
-            Ok(Value::Int(arguments[0].as_int().unwrap() - arguments[1].as_int().unwrap()))
+            Ok(Value::Int(
+                arguments[0].as_int().unwrap() - arguments[1].as_int().unwrap(),
+            ))
         } else {
-            Ok(Value::Float(arguments[0].as_float().unwrap() - arguments[1].as_float().unwrap()))
+            Ok(Value::Float(
+                arguments[0].as_float().unwrap() - arguments[1].as_float().unwrap(),
+            ))
+        }
+    }
+}
+
+impl Operator for Neg {
+    fn precedence(&self) -> i32 {
+        110
+    }
+
+    fn argument_amount(&self) -> usize {
+        1
+    }
+
+    fn eval(&self, arguments: &[Value], _configuration: &Configuration) -> Result<Value, Error> {
+        expect_argument_amount(arguments.len(), 1)?;
+        expect_number(&arguments[0])?;
+
+        if arguments[0].is_int() {
+            Ok(Value::Int(-arguments[0].as_int().unwrap()))
+        } else {
+            Ok(Value::Float(-arguments[0].as_float().unwrap()))
         }
     }
 }
@@ -119,9 +150,13 @@ impl Operator for Mul {
         expect_number(&arguments[1])?;
 
         if arguments[0].is_int() && arguments[1].is_int() {
-            Ok(Value::Int(arguments[0].as_int().unwrap() * arguments[1].as_int().unwrap()))
+            Ok(Value::Int(
+                arguments[0].as_int().unwrap() * arguments[1].as_int().unwrap(),
+            ))
         } else {
-            Ok(Value::Float(arguments[0].as_float().unwrap() * arguments[1].as_float().unwrap()))
+            Ok(Value::Float(
+                arguments[0].as_float().unwrap() * arguments[1].as_float().unwrap(),
+            ))
         }
     }
 }
@@ -141,9 +176,13 @@ impl Operator for Div {
         expect_number(&arguments[1])?;
 
         if arguments[0].is_int() && arguments[1].is_int() {
-            Ok(Value::Int(arguments[0].as_int().unwrap() / arguments[1].as_int().unwrap()))
+            Ok(Value::Int(
+                arguments[0].as_int().unwrap() / arguments[1].as_int().unwrap(),
+            ))
         } else {
-            Ok(Value::Float(arguments[0].as_float().unwrap() / arguments[1].as_float().unwrap()))
+            Ok(Value::Float(
+                arguments[0].as_float().unwrap() / arguments[1].as_float().unwrap(),
+            ))
         }
     }
 }
@@ -179,3 +218,18 @@ impl Operator for Identifier {
         configuration.get_value(&self.identifier)
     }
 }
+
+impl Operator for Braced {
+    fn precedence(&self) -> i32 {
+        200
+    }
+
+    fn argument_amount(&self) -> usize {
+        1
+    }
+
+    fn eval(&self, arguments: &[Value], configuration: &Configuration) -> Result<Value, Error> {
+        expect_argument_amount(arguments.len(), 1)?;
+        Ok(arguments[0].clone())
+    }
+}
diff --git a/src/token/mod.rs b/src/token/mod.rs
index 7b85819..7605e85 100644
--- a/src/token/mod.rs
+++ b/src/token/mod.rs
@@ -1,4 +1,4 @@
-use value::{IntType, FloatType};
+use value::{FloatType, IntType};
 
 #[derive(Clone, PartialEq)]
 pub enum Token {
@@ -7,6 +7,8 @@ pub enum Token {
     Minus,
     Star,
     Slash,
+    LBrace,
+    RBrace,
     Whitespace,
 
     // Complex tokens
@@ -28,6 +30,8 @@ fn char_to_token(c: char) -> PartialToken {
         '-' => PartialToken::Token(Token::Minus),
         '*' => PartialToken::Token(Token::Star),
         '/' => PartialToken::Token(Token::Slash),
+        '(' => PartialToken::Token(Token::LBrace),
+        ')' => PartialToken::Token(Token::RBrace),
         c => {
             if c.is_whitespace() {
                 PartialToken::Token(Token::Whitespace)
@@ -38,6 +42,25 @@ fn char_to_token(c: char) -> PartialToken {
     }
 }
 
+impl Token {
+    // Make this a const fn as soon as match gets stable (issue #57563)
+    pub fn is_value(&self) -> bool {
+        match self {
+            Token::Plus => false,
+            Token::Minus => false,
+            Token::Star => false,
+            Token::Slash => false,
+            Token::LBrace => false,
+            Token::RBrace => true,
+            Token::Whitespace => false,
+            Token::Identifier(_) => true,
+            Token::Float(_) => true,
+            Token::Int(_) => true,
+            Token::Boolean(_) => true,
+        }
+    }
+}
+
 /// Converts a string to a vector of partial tokens.
 fn str_to_tokens(string: &str) -> Vec<PartialToken> {
     let mut result = Vec::new();
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 67d4c8f..e10e230 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -7,18 +7,19 @@ pub struct Node {
 }
 
 impl Node {
-    fn new(operator: Box<dyn Operator>) -> Self {
+    fn new<T: Operator + 'static>(operator: T) -> Self {
         Self {
             children: Vec::new(),
-            operator,
+            operator: Box::new(operator),
         }
     }
 
     fn root_node() -> Self {
-        Self {
-            children: Vec::new(),
-            operator: Box::new(RootNode),
-        }
+        Self::new(RootNode)
+    }
+    
+    fn braced_node() -> Self {
+        Self::new(Braced)
     }
 
     pub fn eval(&self, configuration: &Configuration) -> Result<Value, Error> {
@@ -41,32 +42,31 @@ impl Node {
         self.children().len() == self.operator().argument_amount()
     }
 
-    fn insert_back_prioritized(&mut self, operator: Box<dyn Operator>) -> Result<(), Error> {
-        if self.operator().precedence() < operator.precedence() {
+    fn insert_back_prioritized(&mut self, node: Node, is_root_node: bool) -> Result<(), Error> {
+        if self.operator().precedence() < node.operator().precedence() || is_root_node {
             if self.operator().is_leaf() {
                 Err(Error::AppendedToLeafNode)
             } else if self.has_correct_amount_of_children() {
-                if self.children.last_mut().unwrap().operator().precedence() < operator.precedence()
+                if self.children.last_mut().unwrap().operator().precedence() < node.operator().precedence()
                 {
                     self.children
                         .last_mut()
                         .unwrap()
-                        .insert_back_prioritized(operator)
+                        .insert_back_prioritized(node, false)
                 } else {
-                    let new_node = Node::new(operator);
                     let last_child = self.children.pop().unwrap();
-                    self.children.push(new_node);
-                    let new_node = self.children.last_mut().unwrap();
+                    self.children.push(node);
+                    let node = self.children.last_mut().unwrap();
 
-                    if new_node.operator().is_leaf() {
+                    if node.operator().is_leaf() {
                         Err(Error::AppendedToLeafNode)
                     } else {
-                        new_node.children.push(last_child);
+                        node.children.push(last_child);
                         Ok(())
                     }
                 }
             } else {
-                self.children.push(Node::new(operator));
+                self.children.push(node);
                 Ok(())
             }
         } else {
@@ -76,29 +76,62 @@ impl Node {
 }
 
 pub fn tokens_to_operator_tree(tokens: Vec<Token>) -> Result<Node, Error> {
-    let mut root = Node::root_node();
+    let mut root = vec![Node::root_node()];
+    let mut last_non_whitespace_token_is_value = false;
 
     for token in tokens {
-        let operator: Option<Box<dyn Operator>> = match token {
-            Token::Plus => Some(Box::new(Add)),
-            Token::Minus => Some(Box::new(Sub)),
-            Token::Star => Some(Box::new(Mul)),
-            Token::Slash => Some(Box::new(Div)),
+        let node = match token.clone() {
+            Token::Plus => Some(Node::new(Add)),
+            Token::Minus => {
+                if last_non_whitespace_token_is_value {
+                    Some(Node::new(Sub))
+                } else {
+                    Some(Node::new(Neg))
+                }
+            }
+            Token::Star => Some(Node::new(Mul)),
+            Token::Slash => Some(Node::new(Div)),
+            Token::LBrace => {
+                root.push(Node::braced_node());
+                None
+            },
+            Token::RBrace => {
+                if root.len() < 2 {
+                    return Err(Error::UnmatchedRBrace);
+                } else {
+                    root.pop()
+                }
+            }
             Token::Whitespace => None,
-            Token::Identifier(identifier) => Some(Box::new(Identifier::new(identifier))),
-            Token::Float(number) => Some(Box::new(Const::new(Value::Float(number)))),
-            Token::Int(number) => Some(Box::new(Const::new(Value::Int(number)))),
-            Token::Boolean(boolean) => Some(Box::new(Const::new(Value::Boolean(boolean)))),
+            Token::Identifier(identifier) => Some(Node::new(Identifier::new(identifier))),
+            Token::Float(number) => Some(Node::new(Const::new(Value::Float(number)))),
+            Token::Int(number) => Some(Node::new(Const::new(Value::Int(number)))),
+            Token::Boolean(boolean) => Some(Node::new(Const::new(Value::Boolean(boolean)))),
         };
 
-        if let Some(operator) = operator {
-            root.insert_back_prioritized(operator)?;
+        if let Some(node) = node {
+            if let Some(root) = root.last_mut() {
+                root.insert_back_prioritized(node, true)?;
+            } else {
+                return Err(Error::UnmatchedRBrace);
+            }
+        }
+
+        if token != Token::Whitespace {
+            last_non_whitespace_token_is_value = token.is_value();
         }
     }
 
-    if root.children().len() == 1 {
-        Ok(root.children.pop().unwrap())
+    if root.len() > 1 {
+        Err(Error::UnmatchedLBrace)
+    } else if root.len() == 0 {
+        Err(Error::UnmatchedRBrace)
     } else {
-        Err(Error::EmptyExpression)
+        let mut root = root.pop().unwrap();
+        if root.children().len() == 1 {
+            Ok(root.children.pop().unwrap())
+        } else {
+            Err(Error::EmptyExpression)
+        }
     }
 }
diff --git a/src/value/mod.rs b/src/value/mod.rs
index 482b18f..170ab0e 100644
--- a/src/value/mod.rs
+++ b/src/value/mod.rs
@@ -41,9 +41,3 @@ impl Value {
         }
     }
 }
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Number {
-    Float(FloatType),
-    Int(IntType),
-}
\ No newline at end of file