diff --git a/src/nodes/eval.rs b/src/nodes/eval.rs
index cd37cb3..ea06c2b 100644
--- a/src/nodes/eval.rs
+++ b/src/nodes/eval.rs
@@ -7,8 +7,6 @@ use crate::nodes::{Function, Node, Nodes, Operator};
 
 #[derive(Clone, Debug, thiserror::Error)]
 pub enum Error {
-    #[error("out of bounds: index {0}, {1}")]
-    OutOfBounds(Nodes, usize),
     #[error("invalid operand: {0}")]
     InvalidOperand(Node),
     #[error("missing argument, got: {0}")]
@@ -50,27 +48,22 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
         })
         .next()
     {
-        let Some(node) = nodes.get_mut(start + index + 1) else {
-            return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + index + 1));
-        };
+        match &mut nodes[start..end][index + 1] {
+            Node::Number(n) => match variant {
+                Function::Sqrt => n.sqrt_mut(),
 
-        let Node::Number(n) = node else {
-            return Err(Error::MissingArgument(node.clone()));
-        };
+                Function::Ln => n.ln_mut(),
 
-        match variant {
-            Function::Sqrt => n.sqrt_mut(),
-
-            Function::Ln => n.ln_mut(),
-
-            Function::Sine => n.sin_mut(),
-            Function::ArcSine => n.asin_mut(),
-            Function::Cosine => n.cos_mut(),
-            Function::ArcCosine => n.acos_mut(),
-            Function::Tangent => n.tan_mut(),
-            Function::ArcTangent => n.atan_mut(),
-            Function::Secant => n.sec_mut(),
-            Function::CoSecant => n.csc_mut(),
+                Function::Sine => n.sin_mut(),
+                Function::ArcSine => n.asin_mut(),
+                Function::Cosine => n.cos_mut(),
+                Function::ArcCosine => n.acos_mut(),
+                Function::Tangent => n.tan_mut(),
+                Function::ArcTangent => n.atan_mut(),
+                Function::Secant => n.sec_mut(),
+                Function::CoSecant => n.csc_mut(),
+            },
+            n => return Err(Error::MissingArgument(n.clone())),
         };
 
         nodes.remove(start + index);
@@ -86,11 +79,9 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.pow_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
+        match &mut nodes[start..end][operator] {
+            Node::Number(n) => n.pow_from(lhs),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -106,11 +97,9 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.div_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
+        match &mut nodes[start..end][operator] {
+            Node::Number(n) => n.div_from(lhs),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -126,11 +115,9 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.mul_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
+        match &mut nodes[start..end][operator] {
+            Node::Number(n) => n.mul_from(lhs),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -146,11 +133,9 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.sub_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
+        match &mut nodes[start..end][operator] {
+            Node::Number(n) => n.sub_from(lhs),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);
@@ -166,11 +151,9 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             n => return Err(Error::InvalidOperand(n)),
         };
         end -= 1;
-        match nodes.get_mut(start + operator) {
-            None => return Err(Error::OutOfBounds(Nodes(nodes.clone()), start + operator)),
-
-            Some(Node::Number(n)) => n.add_from(lhs),
-            Some(n) => return Err(Error::InvalidOperand(n.clone())),
+        match &mut nodes[start..end][operator] {
+            Node::Number(n) => n.add_from(lhs),
+            n => return Err(Error::InvalidOperand(n.clone())),
         };
 
         nodes.remove(start + operator - 1);