diff --git a/src/tree/iter.rs b/src/tree/iter.rs
index abae1ad..d812001 100644
--- a/src/tree/iter.rs
+++ b/src/tree/iter.rs
@@ -1,4 +1,4 @@
-use crate::{Node, operator::Operator};
+use crate::{operator::Operator, Node};
 use std::slice::{Iter, IterMut};
 
 /// An iterator that traverses an operator tree in pre-order.
@@ -49,7 +49,7 @@ pub struct OperatorIterMut<'a> {
 impl<'a> OperatorIterMut<'a> {
     fn new(node: &'a mut Node) -> Self {
         OperatorIterMut {
-            stack: vec![node.children.iter_mut()]
+            stack: vec![node.children.iter_mut()],
         }
     }
 }
@@ -92,4 +92,3 @@ impl Node {
         OperatorIterMut::new(self)
     }
 }
-
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 35a3f96..5580031 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -98,12 +98,13 @@ impl Node {
     /// assert_eq!(iter.next(), None);
     /// ```
     pub fn iter_identifiers_mut(&mut self) -> impl Iterator<Item = &mut String> {
-        self.iter_operator_mut().filter_map(|operator| match operator {
-            Operator::VariableIdentifierWrite { identifier }
-            | Operator::VariableIdentifierRead { identifier }
-            | Operator::FunctionIdentifier { identifier } => Some(identifier),
-            _ => None
-        })
+        self.iter_operator_mut()
+            .filter_map(|operator| match operator {
+                Operator::VariableIdentifierWrite { identifier }
+                | Operator::VariableIdentifierRead { identifier }
+                | Operator::FunctionIdentifier { identifier } => Some(identifier),
+                _ => None,
+            })
     }
 
     /// Returns an iterator over all variable identifiers in this expression.
@@ -152,11 +153,12 @@ impl Node {
     /// assert_eq!(iter.next(), None);
     /// ```
     pub fn iter_variable_identifiers_mut(&mut self) -> impl Iterator<Item = &mut String> {
-        self.iter_operator_mut().filter_map(|operator| match operator {
-            Operator::VariableIdentifierWrite { identifier }
-            | Operator::VariableIdentifierRead { identifier } => Some(identifier),
-            _ => None,
-        })
+        self.iter_operator_mut()
+            .filter_map(|operator| match operator {
+                Operator::VariableIdentifierWrite { identifier }
+                | Operator::VariableIdentifierRead { identifier } => Some(identifier),
+                _ => None,
+            })
     }
 
     /// Returns an iterator over all read variable identifiers in this expression.
@@ -205,10 +207,11 @@ impl Node {
     /// assert_eq!(iter.next(), None);
     /// ```
     pub fn iter_read_variable_identifiers_mut(&mut self) -> impl Iterator<Item = &mut String> {
-        self.iter_operator_mut().filter_map(|operator| match operator {
-            Operator::VariableIdentifierRead { identifier } => Some(identifier),
-            _ => None,
-        })
+        self.iter_operator_mut()
+            .filter_map(|operator| match operator {
+                Operator::VariableIdentifierRead { identifier } => Some(identifier),
+                _ => None,
+            })
     }
 
     /// Returns an iterator over all write variable identifiers in this expression.
@@ -255,10 +258,11 @@ impl Node {
     /// assert_eq!(iter.next(), None);
     /// ```
     pub fn iter_write_variable_identifiers_mut(&mut self) -> impl Iterator<Item = &mut String> {
-        self.iter_operator_mut().filter_map(|operator| match operator {
-            Operator::VariableIdentifierWrite { identifier } => Some(identifier),
-            _ => None,
-        })
+        self.iter_operator_mut()
+            .filter_map(|operator| match operator {
+                Operator::VariableIdentifierWrite { identifier } => Some(identifier),
+                _ => None,
+            })
     }
 
     /// Returns an iterator over all function identifiers in this expression.
@@ -305,10 +309,11 @@ impl Node {
     /// assert_eq!(iter.next(), None);
     /// ```
     pub fn iter_function_variable_identifiers_mut(&mut self) -> impl Iterator<Item = &mut String> {
-        self.iter_operator_mut().filter_map(|operator| match operator {
-            Operator::FunctionIdentifier { identifier } => Some(identifier),
-            _ => None,
-        })
+        self.iter_operator_mut()
+            .filter_map(|operator| match operator {
+                Operator::FunctionIdentifier { identifier } => Some(identifier),
+                _ => None,
+            })
     }
 
     /// Evaluates the operator tree rooted at this node with the given context.