diff --git a/src/executor.rs b/src/executor.rs
index 8b5b429..fbe8c17 100644
--- a/src/executor.rs
+++ b/src/executor.rs
@@ -75,11 +75,11 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
 
     fn exec(
         &mut self,
-        tree: ParseTree,
+        tree: Box<ParseTree>,
         locals: &mut Cow<HashMap<String, Object>>) -> Result<Value, RuntimeError>
     {
-        match tree {
-            ParseTree::Add(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+        match *tree {
+            ParseTree::Add(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x + y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x + y as f64)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 + y)),
@@ -87,14 +87,14 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 (Value::String(x), Value::String(y)) => Ok(Value::String(format!("{x}{y}"))),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("+".into(), vec![x, y]))
             },
-            ParseTree::Sub(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::Sub(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x - y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x - y as f64)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 - y)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x - y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("-".into(), vec![x, y]))
             },
-            ParseTree::Mul(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::Mul(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x * y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x * y as f64)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 * y)),
@@ -102,28 +102,28 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 (Value::String(x), Value::Int(y)) => Ok(Value::String(x.repeat(y as usize))),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("*".into(), vec![x, y]))
             },
-            ParseTree::Div(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::Div(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x / y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x / y as f64)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 / y)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x / y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("*".into(), vec![x, y]))
             },
-            ParseTree::Exp(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::Exp(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x.pow(y as u32))),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float((x as f64).powf(y))),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x.powf(y as f64))),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x.powf(y))),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("**".into(), vec![x, y])),
             },
-            ParseTree::Mod(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::Mod(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Int(x % y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Float(x % y as f64)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Float(x as f64 % y)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Float(x % y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("%".into(), vec![x, y])),
             },
-            ParseTree::EqualTo(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::EqualTo(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x == y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool(x as f64 == y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Bool(x == y as f64)),
@@ -132,35 +132,35 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 (Value::String(x), Value::String(y)) => Ok(Value::Bool(x == y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("==".into(), vec![x, y])),
             },
-            ParseTree::GreaterThan(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::GreaterThan(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x > y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool(x as f64 > y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Bool(x > y as f64)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Bool(x > y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes(">".into(), vec![x, y])),
             },
-            ParseTree::GreaterThanOrEqualTo(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::GreaterThanOrEqualTo(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x >= y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool(x as f64 >= y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Bool(x >= y as f64)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Bool(x >= y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes(">=".into(), vec![x, y])),
             },
-            ParseTree::LessThan(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::LessThan(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x < y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool((x as f64) < y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Bool(x < y as f64)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Bool(x < y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("<".into(), vec![x, y])),
             },
-            ParseTree::LessThanOrEqualTo(x, y) => match (self.exec(*x, locals)?, self.exec(*y, locals)?) {
+            ParseTree::LessThanOrEqualTo(x, y) => match (self.exec(x, locals)?, self.exec(y, locals)?) {
                 (Value::Int(x), Value::Int(y)) => Ok(Value::Bool(x <= y)),
                 (Value::Int(x), Value::Float(y)) => Ok(Value::Bool(x as f64 <= y)),
                 (Value::Float(x), Value::Int(y)) => Ok(Value::Bool(x <= y as f64)),
                 (Value::Float(x), Value::Float(y)) => Ok(Value::Bool(x <= y)),
                 (x, y) => Err(RuntimeError::NoOverloadForTypes("<=".into(), vec![x, y])),
             },
-            ParseTree::Not(x) => match self.exec(*x, locals)? {
+            ParseTree::Not(x) => match self.exec(x, locals)? {
                 Value::Bool(x) => Ok(Value::Bool(!x)),
                 x => Err(RuntimeError::NoOverloadForTypes("not".into(), vec![x]))
             },
@@ -169,10 +169,10 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                     Err(RuntimeError::ImmutableError(ident.clone()))
                 } else {
                     let locals = locals.to_mut();
-                    let value = self.exec(*body, &mut Cow::Borrowed(&locals))?;
+                    let value = self.exec(body, &mut Cow::Borrowed(&locals))?;
                     locals.insert(ident.clone(), Object::Variable(Evaluation::Computed(value)));
 
-                    self.exec(*scope, &mut Cow::Borrowed(&locals))
+                    self.exec(scope, &mut Cow::Borrowed(&locals))
                 }
             },
             ParseTree::LazyEqu(ident, body, scope) => {
@@ -182,7 +182,7 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                     let locals = locals.to_mut();
                     locals.insert(ident.clone(), Object::Variable(Evaluation::Uncomputed(body)));
 
-                    self.exec(*scope, &mut Cow::Borrowed(&locals))
+                    self.exec(scope, &mut Cow::Borrowed(&locals))
                 }
             },
             ParseTree::FunctionDefinition(ident, args, r, body, scope) => {
@@ -198,36 +198,36 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                             body: Some(body)
                         }));
 
-                        self.exec(*scope, &mut Cow::Borrowed(&locals))
+                        self.exec(scope, &mut Cow::Borrowed(&locals))
                     }
                 }
             },
             ParseTree::Compose(x, y) => {
-                self.exec(*x, locals)?;
-                self.exec(*y, locals)
+                self.exec(x, locals)?;
+                self.exec(y, locals)
             },
-            ParseTree::Id(x) => self.exec(*x, locals),
-            ParseTree::If(cond, body) => if match self.exec(*cond, locals)? {
+            ParseTree::Id(x) => self.exec(x, locals),
+            ParseTree::If(cond, body) => if match self.exec(cond, locals)? {
                     Value::Float(f) => f != 0.0,
                     Value::Int(i) => i != 0,
                     Value::Bool(b) => b,
                     Value::String(s) => !s.is_empty(),
                     Value::Nil => false,
                 } {
-                    self.exec(*body, locals)
+                    self.exec(body, locals)
                 } else {
                     Ok(Value::Nil)
                 },
-            ParseTree::IfElse(cond, istrue, isfalse) => if match self.exec(*cond, locals)? {
+            ParseTree::IfElse(cond, istrue, isfalse) => if match self.exec(cond, locals)? {
                 Value::Float(f) => f != 0.0,
                 Value::Int(i) => i != 0,
                 Value::Bool(b) => b,
                 Value::String(s) => !s.is_empty(),
                 Value::Nil => false,
             } {
-                self.exec(*istrue, locals)
+                self.exec(istrue, locals)
             } else {
-                self.exec(*isfalse, locals)
+                self.exec(isfalse, locals)
             },
             ParseTree::FunctionCall(ident, args) => {
                 let obj = locals.get(&ident).or(self.globals.get(&ident)).cloned();
@@ -237,10 +237,10 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                     let body = f.body.ok_or(RuntimeError::FunctionUndefined(ident.clone()))?;
 
                     for ((name, _), tree) in std::iter::zip(f.decl.args, args) {
-                        locals.insert(name.clone(), Object::Variable(Evaluation::Computed(self.exec(tree, &mut Cow::Borrowed(locals))?)));
+                        locals.insert(name.clone(), Object::Variable(Evaluation::Computed(self.exec(Box::new(tree), &mut Cow::Borrowed(locals))?)));
                     }
 
-                    self.exec(*body, &mut Cow::Borrowed(&locals))
+                    self.exec(body, &mut Cow::Borrowed(&locals))
                 } else {
                     Err(RuntimeError::FunctionUndeclared(ident.clone()))
                 }
@@ -254,7 +254,7 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                     match eval {
                         Evaluation::Computed(v) => Ok(v),
                         Evaluation::Uncomputed(tree) => {
-                            let v = self.exec(*tree, &mut Cow::Borrowed(&locals))?;
+                            let v = self.exec(tree, &mut Cow::Borrowed(&locals))?;
                             locals.insert(ident, Object::Variable(Evaluation::Computed(v.clone())));
 
                             Ok(v)
@@ -265,7 +265,7 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 }
             },
             ParseTree::Constant(value) => Ok(value),
-            ParseTree::ToInt(x) => match self.exec(*x, locals)? {
+            ParseTree::ToInt(x) => match self.exec(x, locals)? {
                 Value::Int(x) => Ok(Value::Int(x)),
                 Value::Float(x) => Ok(Value::Int(x as i64)),
                 Value::Bool(x) => Ok(Value::Int(if x { 1 } else { 0 })),
@@ -275,7 +275,7 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 }
                 x => Err(RuntimeError::NoOverloadForTypes("int".into(), vec![x])),
             },
-            ParseTree::ToFloat(x) => match self.exec(*x, locals)? {
+            ParseTree::ToFloat(x) => match self.exec(x, locals)? {
                 Value::Int(x) => Ok(Value::Float(x as f64)),
                 Value::Float(x) => Ok(Value::Float(x)),
                 Value::Bool(x) => Ok(Value::Float(if x { 1.0 } else { 0.0 })),
@@ -285,14 +285,14 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Executor<I> {
                 }
                 x => Err(RuntimeError::NoOverloadForTypes("float".into(), vec![x])),
             },
-            ParseTree::ToBool(x) => match self.exec(*x, locals)? {
+            ParseTree::ToBool(x) => match self.exec(x, locals)? {
                 Value::Int(x) => Ok(Value::Bool(x != 0)),
                 Value::Float(x) => Ok(Value::Bool(x != 0.0)),
                 Value::Bool(x) => Ok(Value::Bool(x)),
                 Value::String(x) => Ok(Value::Bool(!x.is_empty())),
                 x => Err(RuntimeError::NoOverloadForTypes("bool".into(), vec![x])),
             },
-            ParseTree::ToString(x) => Ok(Value::String(format!("{}", self.exec(*x, locals)?))),
+            ParseTree::ToString(x) => Ok(Value::String(format!("{}", self.exec(x, locals)?))),
         }
     }
 }
@@ -304,7 +304,7 @@ impl<I: Iterator<Item = Result<ParseTree, ParseError>>> Iterator for Executor<I>
         let expr = self.exprs.next();
 
         match expr {
-            Some(Ok(expr)) => Some(self.exec(expr, &mut Cow::Borrowed(&HashMap::new()))),
+            Some(Ok(expr)) => Some(self.exec(Box::new(expr), &mut Cow::Borrowed(&HashMap::new()))),
             Some(Err(e)) => Some(Err(RuntimeError::ParseError(e))),
             None => None,
         }