diff --git a/dust-lang/src/instruction.rs b/dust-lang/src/instruction.rs
index 4e5fde9..6c29268 100644
--- a/dust-lang/src/instruction.rs
+++ b/dust-lang/src/instruction.rs
@@ -224,6 +224,21 @@ impl Instruction {
     }
 
     pub fn disassembly_info(&self, chunk: Option<&Chunk>) -> Option<String> {
+        let format_arguments = || {
+            let first_argument = if self.first_argument_is_constant() {
+                format!("C({})", self.first_argument())
+            } else {
+                format!("R({})", self.first_argument())
+            };
+            let second_argument = if self.second_argument_is_constant() {
+                format!("C({})", self.second_argument())
+            } else {
+                format!("R({})", self.second_argument())
+            };
+
+            (first_argument, second_argument)
+        };
+
         let info = match self.operation() {
             Operation::Move => {
                 format!("R({}) = R({})", self.destination(), self.first_argument())
@@ -306,106 +321,43 @@ impl Instruction {
             }
             Operation::Add => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} + {second_argument}",)
             }
             Operation::Subtract => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} - {second_argument}",)
             }
             Operation::Multiply => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} * {second_argument}",)
             }
             Operation::Divide => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} / {second_argument}",)
             }
             Operation::Modulo => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} % {second_argument}",)
             }
             Operation::And => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} && {second_argument}",)
             }
             Operation::Or => {
                 let destination = self.destination();
-                let first_argument = if self.first_argument_is_constant() {
-                    format!("C({})", self.first_argument())
-                } else {
-                    format!("R({})", self.first_argument())
-                };
-                let second_argument = if self.second_argument_is_constant() {
-                    format!("C({})", self.second_argument())
-                } else {
-                    format!("R({})", self.second_argument())
-                };
+                let (first_argument, second_argument) = format_arguments();
 
                 format!("R({destination}) = {first_argument} || {second_argument}",)
             }
diff --git a/dust-lang/src/parser/mod.rs b/dust-lang/src/parser/mod.rs
index b460729..1e495a8 100644
--- a/dust-lang/src/parser/mod.rs
+++ b/dust-lang/src/parser/mod.rs
@@ -96,7 +96,7 @@ impl<'src> Parser<'src> {
 
         let (new_token, position) = self.lexer.next_token()?;
 
-        log::trace!("Parsing token \"{new_token}\" at {position}");
+        log::trace!("Parsing \"{new_token}\" at {position}");
 
         self.previous_token = replace(&mut self.current_token, new_token);
         self.previous_position = replace(&mut self.current_position, position);
@@ -271,7 +271,7 @@ impl<'src> Parser<'src> {
             TokenKind::Minus => Instruction::negate(destination, from_register),
             _ => {
                 return Err(ParseError::ExpectedTokenMultiple {
-                    expected: &[TokenKind::Minus],
+                    expected: &[TokenKind::Bang, TokenKind::Minus],
                     found: operator.to_owned(),
                     position: operator_position,
                 })
@@ -356,6 +356,9 @@ impl<'src> Parser<'src> {
                         TokenKind::Minus,
                         TokenKind::Star,
                         TokenKind::Slash,
+                        TokenKind::Percent,
+                        TokenKind::DoubleAmpersand,
+                        TokenKind::DoublePipe,
                     ],
                     found: operator.to_owned(),
                     position: operator_position,
@@ -475,13 +478,14 @@ impl<'src> Parser<'src> {
     }
 
     fn parse_list(&mut self, _allow_assignment: bool) -> Result<(), ParseError> {
+        let start = self.current_position.0;
+
         self.advance()?;
 
-        let start = self.current_position.0;
         let mut length = 0;
 
         while !self.allow(TokenKind::RightSquareBrace)? && !self.is_eof() {
-            self.parse_expression()?;
+            self.parse(Precedence::Assignment)?; // Do not allow assignment
 
             length += 1;
 
@@ -535,7 +539,14 @@ impl<'src> Parser<'src> {
         Ok(())
     }
 
-    fn parse_let_statement(&mut self, _allow_assignment: bool) -> Result<(), ParseError> {
+    fn parse_let_statement(&mut self, allow_assignment: bool) -> Result<(), ParseError> {
+        if !allow_assignment {
+            return Err(ParseError::ExpectedExpression {
+                found: self.current_token.to_owned(),
+                position: self.current_position,
+            });
+        }
+
         self.advance()?;
 
         let position = self.current_position;
@@ -587,7 +598,7 @@ impl<'src> Parser<'src> {
 
         if let Some(prefix_parser) = ParseRule::from(&self.current_token.kind()).prefix {
             log::trace!(
-                "Parsing {} as prefix with precedence {precedence}",
+                "Parsing \"{}\" with prefix parser at precedence {precedence}",
                 self.current_token,
             );
 
@@ -599,7 +610,7 @@ impl<'src> Parser<'src> {
         while precedence <= infix_rule.precedence {
             if let Some(infix_parser) = infix_rule.infix {
                 log::trace!(
-                    "Parsing {} as infix with precedence {precedence}",
+                    "Parsing \"{}\" with infix parser at precedence {precedence}",
                     self.current_token,
                 );
 
diff --git a/dust-lang/src/vm.rs b/dust-lang/src/vm.rs
index efe678f..95c261b 100644
--- a/dust-lang/src/vm.rs
+++ b/dust-lang/src/vm.rs
@@ -35,6 +35,26 @@ impl Vm {
     }
 
     pub fn run(&mut self) -> Result<Option<Value>, VmError> {
+        let take_constants_or_clone = |vm: &mut Vm,
+                                       instruction: Instruction,
+                                       position: Span|
+         -> Result<(Value, Value), VmError> {
+            let left = if instruction.first_argument_is_constant() {
+                vm.chunk
+                    .take_constant(instruction.first_argument(), position)?
+            } else {
+                vm.clone(instruction.first_argument(), position)?
+            };
+            let right = if instruction.second_argument_is_constant() {
+                vm.chunk
+                    .take_constant(instruction.second_argument(), position)?
+            } else {
+                vm.clone(instruction.second_argument(), position)?
+            };
+
+            Ok((left, right))
+        };
+
         while let Ok((instruction, position)) = self.read(Span(0, 0)).copied() {
             log::trace!("Running instruction {instruction} at {position}");
 
@@ -98,16 +118,7 @@ impl Vm {
                     self.chunk.define_local(to_local, from_register, position)?;
                 }
                 Operation::Add => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let sum = left
                         .add(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -115,16 +126,7 @@ impl Vm {
                     self.insert(sum, instruction.destination(), position)?;
                 }
                 Operation::Subtract => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let difference = left
                         .subtract(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -132,16 +134,7 @@ impl Vm {
                     self.insert(difference, instruction.destination(), position)?;
                 }
                 Operation::Multiply => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let product = left
                         .multiply(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -149,16 +142,7 @@ impl Vm {
                     self.insert(product, instruction.destination(), position)?;
                 }
                 Operation::Divide => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let quotient = left
                         .divide(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -166,16 +150,7 @@ impl Vm {
                     self.insert(quotient, instruction.destination(), position)?;
                 }
                 Operation::Modulo => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let remainder = left
                         .modulo(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -183,16 +158,7 @@ impl Vm {
                     self.insert(remainder, instruction.destination(), position)?;
                 }
                 Operation::And => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let result = left
                         .and(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -200,16 +166,7 @@ impl Vm {
                     self.insert(result, instruction.destination(), position)?;
                 }
                 Operation::Or => {
-                    let left = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
-                    let right = self.take_constant_or_clone_register(
-                        instruction.second_argument(),
-                        instruction.second_argument_is_constant(),
-                        position,
-                    )?;
+                    let (left, right) = take_constants_or_clone(self, instruction, position)?;
                     let result = left
                         .or(&right)
                         .map_err(|error| VmError::Value { error, position })?;
@@ -217,11 +174,12 @@ impl Vm {
                     self.insert(result, instruction.destination(), position)?;
                 }
                 Operation::Negate => {
-                    let value = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
+                    let value = if instruction.first_argument_is_constant() {
+                        self.chunk
+                            .take_constant(instruction.first_argument(), position)?
+                    } else {
+                        self.clone(instruction.first_argument(), position)?
+                    };
                     let negated = value
                         .negate()
                         .map_err(|error| VmError::Value { error, position })?;
@@ -229,11 +187,12 @@ impl Vm {
                     self.insert(negated, instruction.destination(), position)?;
                 }
                 Operation::Not => {
-                    let value = self.take_constant_or_clone_register(
-                        instruction.first_argument(),
-                        instruction.first_argument_is_constant(),
-                        position,
-                    )?;
+                    let value = if instruction.first_argument_is_constant() {
+                        self.chunk
+                            .take_constant(instruction.first_argument(), position)?
+                    } else {
+                        self.clone(instruction.first_argument(), position)?
+                    };
                     let result = value
                         .not()
                         .map_err(|error| VmError::Value { error, position })?;
@@ -289,19 +248,6 @@ impl Vm {
         }
     }
 
-    fn take_constant_or_clone_register(
-        &mut self,
-        index: u8,
-        is_constant: bool,
-        position: Span,
-    ) -> Result<Value, VmError> {
-        if is_constant {
-            Ok(self.chunk.take_constant(index, position)?)
-        } else {
-            self.clone(index, position)
-        }
-    }
-
     fn pop(&mut self, position: Span) -> Result<Value, VmError> {
         if let Some(register) = self.register_stack.pop() {
             let value = register.ok_or(VmError::EmptyRegister {