diff --git a/dust-lang/src/analyzer.rs b/dust-lang/src/analyzer.rs
index b5ea5b1..4eb0ea0 100644
--- a/dust-lang/src/analyzer.rs
+++ b/dust-lang/src/analyzer.rs
@@ -160,7 +160,9 @@ impl<'a> Analyzer<'a> {
                 }
             }
             Statement::Identifier(identifier) => {
-                if !self.context.contains(identifier) {
+                let exists = self.context.add_allowed_use(identifier);
+
+                if !exists {
                     return Err(AnalyzerError::UndefinedVariable {
                         identifier: node.clone(),
                     });
@@ -241,11 +243,6 @@ pub enum AnalyzerError {
         actual: Node<Statement>,
         position: Span,
     },
-    ExpectedSameType {
-        left: Node<Statement>,
-        right: Node<Statement>,
-        position: Span,
-    },
     ExpectedString {
         actual: Node<Statement>,
         position: (usize, usize),
@@ -278,7 +275,6 @@ impl AnalyzerError {
             AnalyzerError::ExpectedInteger { position, .. } => *position,
             AnalyzerError::ExpectedIntegerOrFloat { position, .. } => *position,
             AnalyzerError::ExpectedIntegerFloatOrString { position, .. } => *position,
-            AnalyzerError::ExpectedSameType { position, .. } => *position,
             AnalyzerError::ExpectedString { position, .. } => *position,
             AnalyzerError::UndefinedVariable { identifier } => identifier.position,
             AnalyzerError::UnexpectedIdentifier { position, .. } => *position,
@@ -313,9 +309,6 @@ impl Display for AnalyzerError {
             AnalyzerError::ExpectedIntegerFloatOrString { actual, .. } => {
                 write!(f, "Expected integer, float, or string, found {}", actual)
             }
-            AnalyzerError::ExpectedSameType { left, right, .. } => {
-                write!(f, "Expected same type, found {} and {}", left, right)
-            }
             AnalyzerError::ExpectedString { actual, .. } => {
                 write!(f, "Expected string, found {}", actual)
             }
@@ -341,6 +334,31 @@ mod tests {
 
     use super::*;
 
+    #[test]
+    fn math_requires_same_types() {
+        let abstract_tree = AbstractSyntaxTree {
+            nodes: [Node::new(
+                Statement::BinaryOperation {
+                    left: Box::new(Node::new(Statement::Constant(Value::integer(1)), (0, 1))),
+                    operator: Node::new(BinaryOperator::Add, (1, 2)),
+                    right: Box::new(Node::new(Statement::Constant(Value::float(1.0)), (3, 4))),
+                },
+                (0, 2),
+            )]
+            .into(),
+        };
+        let mut context = Context::new();
+        let mut analyzer = Analyzer::new(&abstract_tree, &mut context);
+
+        assert_eq!(
+            analyzer.analyze(),
+            Err(AnalyzerError::ExpectedInteger {
+                actual: Node::new(Statement::Constant(Value::float(1.0)), (3, 4)),
+                position: (3, 4)
+            })
+        )
+    }
+
     #[test]
     fn float_plus_integer() {
         let abstract_tree = AbstractSyntaxTree {
diff --git a/dust-lang/src/context.rs b/dust-lang/src/context.rs
index cd19f3a..e473ab5 100644
--- a/dust-lang/src/context.rs
+++ b/dust-lang/src/context.rs
@@ -31,9 +31,13 @@ impl Context {
         }
     }
 
-    pub fn get_value(&self, identifier: &Identifier) -> Option<&Value> {
-        match self.variables.get(identifier) {
-            Some((VariableData::Value(value), _)) => Some(value),
+    pub fn use_value(&mut self, identifier: &Identifier) -> Option<&Value> {
+        match self.variables.get_mut(identifier) {
+            Some((VariableData::Value(value), usage_data)) => {
+                usage_data.used += 1;
+
+                Some(value)
+            }
             _ => None,
         }
     }
@@ -63,6 +67,16 @@ impl Context {
         self.variables
             .retain(|_, (_, usage_data)| usage_data.used < usage_data.allowed_uses);
     }
+
+    pub fn add_allowed_use(&mut self, identifier: &Identifier) -> bool {
+        if let Some((_, usage_data)) = self.variables.get_mut(identifier) {
+            usage_data.allowed_uses += 1;
+
+            true
+        } else {
+            false
+        }
+    }
 }
 
 impl Default for Context {
diff --git a/dust-lang/src/vm.rs b/dust-lang/src/vm.rs
index 65577f5..2de4b9d 100644
--- a/dust-lang/src/vm.rs
+++ b/dust-lang/src/vm.rs
@@ -90,7 +90,7 @@ impl Vm {
                             position: right_position,
                         });
                     };
-                    let left_value = context.get_value(&identifier).ok_or_else(|| {
+                    let left_value = context.use_value(&identifier).ok_or_else(|| {
                         VmError::UndefinedVariable {
                             identifier: Node::new(
                                 Statement::Identifier(identifier.clone()),
@@ -236,7 +236,7 @@ impl Vm {
                 Ok(function.clone().call(None, value_parameters, context)?)
             }
             Statement::Identifier(identifier) => {
-                if let Some(value) = context.get_value(&identifier) {
+                if let Some(value) = context.use_value(&identifier) {
                     Ok(Some(value.clone()))
                 } else {
                     Err(VmError::UndefinedVariable {
diff --git a/dust_examples/fizzbuzz.ds b/dust_examples/fizzbuzz.ds
index 2fd54c0..e44083a 100644
--- a/dust_examples/fizzbuzz.ds
+++ b/dust_examples/fizzbuzz.ds
@@ -1,14 +1,12 @@
-use std.io
-
 count = 1
 
 while count <= 15 {
 	divides_by_3 = count % 3 == 0
 	divides_by_5 = count % 5 == 0
 
-	output = if divides_by_3 && divides_by_5 { 
+	output = if divides_by_3 && divides_by_5 {
 		'fizzbuzz'
-	} else if divides_by_3 { 
+	} else if divides_by_3 {
 		'fizz'
 	} else if divides_by_5 {
 		'buzz'
@@ -16,8 +14,7 @@ while count <= 15 {
 		count as str
 	}
 
-	io.write_line(output)
-	
+	write_line(output)
+
 	count += 1
 }
-