diff --git a/src/phase/evaluate.rs b/src/phase/evaluate.rs
index 808d2d6..36bd61c 100644
--- a/src/phase/evaluate.rs
+++ b/src/phase/evaluate.rs
@@ -8,7 +8,11 @@ pub type Dictionary<T> = HashMap<Name, T>;
 
 #[derive(Debug, Clone)]
 pub enum Value {
-    Closure(Dictionary<Value>, Vec<Name>, Expression),
+    Closure {
+        environment: Dictionary<Value>,
+        parameters: Vec<Name>,
+        result: Expression,
+    },
     Boolean(bool),
     Integer(i64),
 }
@@ -19,7 +23,7 @@ pub enum Error {
     UnboundName(Name),
     #[error("Tried to call a term which was not a function")]
     NotAFunction,
-    #[error("Mismatched number of function arguments and parameters: expected {0}, got {1}")]
+    #[error("Mismatched number of function parameters and arguments: expected {0}, got {1}")]
     ArgumentsMismatch(usize, usize),
     #[error("No function called main to run")]
     MissingMainFunction,
@@ -39,13 +43,16 @@ impl Interpreter {
         }
     }
 
+    fn nested(environment: Dictionary<Value>) -> Self {
+        Interpreter { environment }
+    }
+
     pub fn run(&mut self, program: &Program) -> Result<Value> {
         for item in program {
             self.interpret_item(item)?;
         }
-        if let Some(main) = self.environment.get("main") {
-            // should main be an expression? a standalone closure type?
-            todo!()
+        if let Some(main) = self.environment.get("main").cloned() {
+            self.call_closure(&main, &vec![])
         } else {
             Err(Error::MissingMainFunction)
         }
@@ -58,11 +65,11 @@ impl Interpreter {
                 parameters,
                 body,
             } => {
-                let closure = Value::Closure(
-                    self.environment.clone(),
-                    parameters.clone(),
-                    Expression::Block(Box::new(body.clone())),
-                );
+                let closure = Value::Closure {
+                    environment: self.environment.clone(),
+                    parameters: parameters.clone(),
+                    result: Expression::Block(Box::new(body.clone())),
+                };
                 self.environment.insert(name.clone(), closure.clone());
                 Ok(closure)
             }
@@ -87,30 +94,41 @@ impl Interpreter {
                 .ok_or(Error::UnboundName(name.clone()))
                 .cloned(),
             Expression::Block(b) => self.evaluate_block(b.as_ref()),
-            Expression::Lambda { parameters, result } => Ok(Value::Closure(
-                self.environment.clone(),
-                parameters.clone(),
-                *result.clone(),
-            )),
-            Expression::Call { callee, arguments } => match callee.as_ref() {
-                Expression::Lambda { parameters, result } => {
-                    if parameters.len() != arguments.len() {
-                        return Err(Error::ArgumentsMismatch(parameters.len(), arguments.len()));
-                    }
-                    let mut nested = self.clone();
-                    for (name, argument) in parameters.iter().zip(arguments) {
-                        // we don't want arguments to refer to each other, so use the parent interpreter
-                        nested.bind(name.clone(), argument)?;
-                    }
-                    nested.evaluate(result)
-                }
-                _ => Err(Error::NotAFunction),
-            },
+            Expression::Lambda { parameters, result } => Ok(Value::Closure {
+                environment: self.environment.clone(),
+                parameters: parameters.clone(),
+                result: *result.clone(),
+            }),
+            Expression::Call { callee, arguments } => {
+                let callee = self.evaluate(callee.as_ref())?;
+                self.call_closure(&callee, arguments)
+            }
             Expression::Boolean(b) => Ok(Value::Boolean(*b)),
             Expression::Integer(i) => Ok(Value::Integer(*i)),
         }
     }
 
+    fn call_closure(&mut self, callee: &Value, arguments: &Vec<Expression>) -> Result<Value> {
+        match callee {
+            Value::Closure {
+                environment,
+                parameters,
+                result,
+            } => {
+                if parameters.len() != arguments.len() {
+                    return Err(Error::ArgumentsMismatch(parameters.len(), arguments.len()));
+                }
+                let mut nested = Interpreter::nested(environment.clone());
+                for (name, argument) in parameters.iter().zip(arguments) {
+                    // we don't want arguments to refer to each other, so use the parent interpreter
+                    nested.bind(name.clone(), argument)?;
+                }
+                nested.evaluate(result)
+            }
+            _ => Err(Error::NotAFunction),
+        }
+    }
+
     fn evaluate_block(&mut self, block: &Block) -> Result<Value> {
         let mut nested = self.clone();
         for binding in &block.bindings {