diff --git a/examples/array.pr b/examples/array.pr
new file mode 100644
index 0000000..abd9097
--- /dev/null
+++ b/examples/array.pr
@@ -0,0 +1,68 @@
+
+for: (from, to, f) => {
+	index: from;
+	loop {
+		if not(inf(index, to)) break true;
+		f(index);
+		index <- add(index, 1)
+	}
+};
+
+array_new: () => {
+	r: obj();
+	r <- set(r, "len", 0);
+	r
+};
+
+array_len: (self) => {
+	get(self, "len")
+};
+
+array_get: (self, index) => {
+	get(self, str(index))
+};
+
+array_push: (self, e) => {
+	i: array_len(self);
+	self <- set(self, str(i), e);
+
+	len: add (i, 1);
+	self <- set(self, "len", len);
+	self
+};
+
+array_pop: (self) => {
+	l: array_len(self);
+	if eq(l, 0) return false;
+	
+	i: sub(l, 1);
+	e: array_get(self, i);
+	self <- set(self, str(i), false);
+	
+	r: obj();
+	r <- set(r, "tail", e);
+	r <- set(r, "rest", self);
+	r
+};
+
+array_print: (self) => {
+	l: array_len(self);
+	r: "[";
+	for(0, l, (i) => {
+		r <- add(r, array_get(self, i));
+		r <- add(r, ", ")
+	});
+	r <- add(r, "]");
+	out(r)
+};
+
+main: () => {
+	a: array_new();
+	a <- array_push(a, 1);
+	a <- array_push(a, 2);
+	a <- array_push(a, 3);
+	a <- array_push(a, 4);
+	array_print(a)
+};
+
+main();
diff --git a/src/execution_tree/parser.rs b/src/execution_tree/parser.rs
index cf0c394..d7960c0 100644
--- a/src/execution_tree/parser.rs
+++ b/src/execution_tree/parser.rs
@@ -187,7 +187,7 @@ impl Parser {
             parameter_names,
         } = function_definition;
 
-        let parser_scope = parser_scope.make_child_common();
+        let parser_scope = parser_scope.make_child_function();
         let parameter_ids = parameter_names
             .into_iter()
             .map(|name| parser_scope.add_name(name))
@@ -209,7 +209,7 @@ impl Parser {
 
         let variable_id = parser_scope
             .get_variable_id(&name)
-            .expect("call of undeclared function");
+            .expect(&format!("call of undeclared function '{name}'"));
         let parameters = arguments
             .into_iter()
             .map(|argument| self.parse_expression(argument, parser_scope))
diff --git a/src/prelude.rs b/src/prelude.rs
index 433e268..a6a3a71 100644
--- a/src/prelude.rs
+++ b/src/prelude.rs
@@ -132,7 +132,11 @@ fn set(args: Vec<Value>) -> Value {
     let mut object = args.get(0).unwrap().as_object().unwrap().clone();
     let name = args.get(1).unwrap().as_string().unwrap().to_string();
     let value = args.get(2).unwrap().clone();
-    object.insert(name, value);
+    if let Value::Bool(false) = value {
+        object.remove(&name);
+    } else {
+        object.insert(name, value);
+    }
     object.into()
 }
 
diff --git a/src/syntax_tree/parser.rs b/src/syntax_tree/parser.rs
index 64075b6..3ce7100 100644
--- a/src/syntax_tree/parser.rs
+++ b/src/syntax_tree/parser.rs
@@ -142,7 +142,12 @@ fn test_function_definition_parser() {
 pub fn function_call_parser(expression: impl AbstractParser<Expr>) -> impl AbstractParser<FnCall> {
     let parameters = expression.separated_by(just(',').padded());
     name()
-        .then(parameters.padded().delimited_by(just('('), just(')')))
+        .then(
+            parameters
+                .padded()
+                .delimited_by(just('('), just(')'))
+                .padded(),
+        )
         .map(|(name, arguments)| FnCall { arguments, name })
 }
 
diff --git a/src/value.rs b/src/value.rs
index fdfe9a4..463e766 100644
--- a/src/value.rs
+++ b/src/value.rs
@@ -100,13 +100,6 @@ impl Value {
         }
     }
 
-    pub fn as_object_mut(&mut self) -> Option<&mut HashMap<String, Value>> {
-        match self {
-            Self::Object(h) => Some(h),
-            _ => None,
-        }
-    }
-
     pub fn as_function(&self) -> Option<&Function> {
         match self {
             Self::Function(function) => Some(function),