diff --git a/src/bin/expressive.rs b/src/bin/expressive.rs
new file mode 100644
index 0000000..ac1ee3f
--- /dev/null
+++ b/src/bin/expressive.rs
@@ -0,0 +1,7 @@
+pub fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let args = std::env::args().skip(1).collect::<Vec<String>>().join(" ");
+
+    println!("{}", evalexpr::eval(&args)?);
+
+    Ok(())
+}
diff --git a/src/context/mod.rs b/src/context/mod.rs
index 8d562c0..0cf7d84 100644
--- a/src/context/mod.rs
+++ b/src/context/mod.rs
@@ -4,7 +4,7 @@
 //! This crate implements two basic variants, the `EmptyContext`, that returns `None` for each identifier and cannot be manipulated, and the `HashMapContext`, that stores its mappings in hash maps.
 //! The HashMapContext is type-safe and returns an error if the user tries to assign a value of a different type than before to an identifier.
 
-use std::{collections::HashMap, iter};
+use std::collections::BTreeMap;
 
 use crate::{
     function::Function,
@@ -27,7 +27,7 @@ pub trait Context {
 /// A context that allows to assign to variables.
 pub trait ContextWithMutableVariables: Context {
     /// Sets the variable with the given identifier to the given value.
-    fn set_value(&mut self, _identifier: String, _value: Value) -> EvalexprResult<()> {
+    fn set_value(&mut self, _identifier: &str, _value: Value) -> EvalexprResult<()> {
         Err(EvalexprError::ContextNotMutable)
     }
 }
@@ -40,105 +40,81 @@ pub trait ContextWithMutableFunctions: Context {
     }
 }
 
-/// A context that allows to iterate over its variable names with their values.
-///
-/// **Note:** this trait will change after GATs are stabilised, because then we can get rid of the lifetime in the trait definition.
-pub trait IterateVariablesContext {
-    /// The iterator type for iterating over variable name-value pairs.
-    type VariableIterator<'a>: Iterator<Item = (String, Value)>
-    where
-        Self: 'a;
-    /// The iterator type for iterating over variable names.
-    type VariableNameIterator<'a>: Iterator<Item = String>
-    where
-        Self: 'a;
-
-    /// Returns an iterator over pairs of variable names and values.
-    fn iter_variables(&self) -> Self::VariableIterator<'_>;
-
-    /// Returns an iterator over variable names.
-    fn iter_variable_names(&self) -> Self::VariableNameIterator<'_>;
-}
-
 /// A context that stores its mappings in hash maps.
-///
-/// *Value and function mappings are stored independently, meaning that there can be a function and a value with the same identifier.*
-///
-/// This context is type-safe, meaning that an identifier that is assigned a value of some type once cannot be assigned a value of another type.
 #[derive(Clone, Debug, Default)]
-pub struct ContextData {
-    map_name: String,
-
-    variables: HashMap<String, Value>,
-
-    functions: HashMap<String, Function>,
+pub struct VariableMap {
+    variables: BTreeMap<String, Value>,
 }
 
-impl ContextData {
-    /// Constructs a `HashMapContext` with no mappings.
+impl PartialEq for VariableMap {
+    fn eq(&self, other: &Self) -> bool {
+        if self.variables.len() != other.variables.len() {
+            return false;
+        }
+
+        for variable in &self.variables {
+            for other in &other.variables {
+                if variable != other {
+                    return false;
+                }
+            }
+        }
+
+        true
+    }
+}
+
+impl VariableMap {
+    /// Create a new instace.
     pub fn new() -> Self {
         Default::default()
     }
 }
 
-impl Context for ContextData {
+impl Context for VariableMap {
     fn get_value(&self, identifier: &str) -> Option<&Value> {
         self.variables.get(identifier)
     }
 
     fn call_function(&self, identifier: &str, argument: &Value) -> EvalexprResult<Value> {
         match identifier {
-            "map" => {
-                let map = Value::Map(self.variables.clone());
-                self.variables.insert(identifier.to_string(), map);
-                Ok(Value::Empty)
-            },
             _ => todo!(),
         }
     }
-
 }
 
-impl ContextWithMutableVariables for ContextData {
-    fn set_value(&mut self, identifier: String, value: Value) -> EvalexprResult<()> {
-        if let Some(existing_value) = self.variables.get_mut(&identifier) {
-            if ValueType::from(&existing_value) == ValueType::from(&value) {
-                *existing_value = value;
-                return Ok(());
+impl ContextWithMutableVariables for VariableMap {
+    fn set_value(&mut self, identifier: &str, value: Value) -> EvalexprResult<()> {
+        println!("{:#?}", self);
+        println!("{}", identifier);
+
+        let split = identifier.split_once(".");
+        if let Some((map_name, next_identifier)) = split {
+            if let Some(map_value) = self.variables.get_mut(map_name) {
+                if let Value::Map(map) = map_value {
+                    map.set_value(next_identifier, value)?;
+                } else {
+                    return Err(EvalexprError::ExpectedMap {
+                        actual: map_value.clone(),
+                    });
+                }
             } else {
-                return Err(EvalexprError::expected_type(existing_value, value));
+                let mut new_map = BTreeMap::new();
+                new_map.insert(next_identifier.to_string(), value);
+                let map_var = Value::Map(VariableMap { variables: new_map });
+                self.variables.insert(map_name.to_string(), map_var);
             }
+        } else {
+            self.variables.insert(identifier.to_string(), value);
         }
 
-        // Implicit else, because `self.variables` and `identifier` are not unborrowed in else
-        self.variables.insert(identifier, value);
         Ok(())
     }
 }
 
-impl ContextWithMutableFunctions for ContextData {
+impl ContextWithMutableFunctions for VariableMap {
     fn set_function(&mut self, identifier: String, function: Function) -> EvalexprResult<()> {
-        self.functions.insert(identifier, function);
-        Ok(())
-    }
-}
-
-impl IterateVariablesContext for ContextData {
-    type VariableIterator<'a> = std::iter::Map<
-        std::collections::hash_map::Iter<'a, String, Value>,
-        fn((&String, &Value)) -> (String, Value),
-    >;
-    type VariableNameIterator<'a> =
-        std::iter::Cloned<std::collections::hash_map::Keys<'a, String, Value>>;
-
-    fn iter_variables(&self) -> Self::VariableIterator<'_> {
-        self.variables
-            .iter()
-            .map(|(string, value)| (string.clone(), value.clone()))
-    }
-
-    fn iter_variable_names(&self) -> Self::VariableNameIterator<'_> {
-        self.variables.keys().cloned()
+        todo!()
     }
 }
 
@@ -179,7 +155,7 @@ macro_rules! context_map {
 
     // Create a context, then recurse to add the values in it
     ( $($tt:tt)* ) => {{
-        let mut context = $crate::HashMapContext::new();
+        let mut context = $crate::VariableMap::new();
         $crate::context_map!((&mut context) $($tt)*)
             .map(|_| context)
     }};
diff --git a/src/function/builtin.rs b/src/function/builtin.rs
index fb64060..9fc66b7 100644
--- a/src/function/builtin.rs
+++ b/src/function/builtin.rs
@@ -5,7 +5,10 @@ use crate::{
     value::{FloatType, IntType},
     EvalexprError, Function, Value, ValueType,
 };
-use std::ops::{BitAnd, BitOr, BitXor, Not, Shl, Shr};
+use std::{
+    collections::HashSet,
+    ops::{BitAnd, BitOr, BitXor, Not, Shl, Shr},
+};
 
 macro_rules! simple_math {
     ($func:ident) => {
diff --git a/src/interface/mod.rs b/src/interface/mod.rs
index 3650255..b64f8cf 100644
--- a/src/interface/mod.rs
+++ b/src/interface/mod.rs
@@ -1,6 +1,6 @@
 use crate::{
     token, tree, value::TupleType, Context, ContextWithMutableVariables, EmptyType, EvalexprError,
-    EvalexprResult, FloatType, ContextData, IntType, Node, Value, EMPTY_VALUE,
+    EvalexprResult, FloatType, IntType, Node, Value, VariableMap, EMPTY_VALUE,
 };
 
 /// Evaluate the given expression string.
@@ -15,7 +15,7 @@ use crate::{
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval(string: &str) -> EvalexprResult<Value> {
-    eval_with_context_mut(string, &mut ContextData::new())
+    eval_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string with the given context.
@@ -91,21 +91,21 @@ pub fn build_operator_tree(string: &str) -> EvalexprResult<Node> {
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_string(string: &str) -> EvalexprResult<String> {
-    eval_string_with_context_mut(string, &mut ContextData::new())
+    eval_string_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into an integer.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_int(string: &str) -> EvalexprResult<IntType> {
-    eval_int_with_context_mut(string, &mut ContextData::new())
+    eval_int_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into a float.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_float(string: &str) -> EvalexprResult<FloatType> {
-    eval_float_with_context_mut(string, &mut ContextData::new())
+    eval_float_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into a float.
@@ -113,28 +113,28 @@ pub fn eval_float(string: &str) -> EvalexprResult<FloatType> {
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_number(string: &str) -> EvalexprResult<FloatType> {
-    eval_number_with_context_mut(string, &mut ContextData::new())
+    eval_number_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into a boolean.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_boolean(string: &str) -> EvalexprResult<bool> {
-    eval_boolean_with_context_mut(string, &mut ContextData::new())
+    eval_boolean_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into a tuple.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_tuple(string: &str) -> EvalexprResult<TupleType> {
-    eval_tuple_with_context_mut(string, &mut ContextData::new())
+    eval_tuple_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into an empty value.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
 pub fn eval_empty(string: &str) -> EvalexprResult<EmptyType> {
-    eval_empty_with_context_mut(string, &mut ContextData::new())
+    eval_empty_with_context_mut(string, &mut VariableMap::new())
 }
 
 /// Evaluate the given expression string into a string with the given context.
diff --git a/src/lib.rs b/src/lib.rs
index e352b4a..2bf53a5 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -560,9 +560,7 @@ extern crate serde;
 extern crate serde_derive;
 
 pub use crate::{
-    context::{
-        Context, ContextWithMutableFunctions, ContextWithMutableVariables, ContextData, IterateVariablesContext,
-    },
+    context::{Context, ContextWithMutableFunctions, ContextWithMutableVariables, VariableMap},
     error::{EvalexprError, EvalexprResult},
     function::Function,
     interface::*,
diff --git a/src/operator/mod.rs b/src/operator/mod.rs
index 31f13b2..9c8825d 100644
--- a/src/operator/mod.rs
+++ b/src/operator/mod.rs
@@ -459,8 +459,7 @@ impl Operator {
                 let arguments = &arguments[0];
 
                 match context.call_function(identifier, arguments) {
-                    Err(EvalexprError::FunctionIdentifierNotFound(_)) =>
-                    {
+                    Err(EvalexprError::FunctionIdentifierNotFound(_)) => {
                         if let Some(builtin_function) = builtin_function(identifier) {
                             builtin_function.call(arguments)
                         } else {
@@ -486,7 +485,7 @@ impl Operator {
             Assign => {
                 expect_operator_argument_amount(arguments.len(), 2)?;
                 let target = arguments[0].as_string()?;
-                context.set_value(target, arguments[1].clone())?;
+                context.set_value(&target, arguments[1].clone())?;
 
                 Ok(Value::Empty)
             },
@@ -515,7 +514,7 @@ impl Operator {
                         self
                     ),
                 }?;
-                context.set_value(target, result)?;
+                context.set_value(&target, result)?;
 
                 Ok(Value::Empty)
             },
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index 5422305..8c13bc4 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -1,7 +1,7 @@
 use crate::{
     token::Token,
     value::{TupleType, EMPTY_VALUE},
-    Context, ContextWithMutableVariables, EmptyType, FloatType, ContextData, IntType,
+    Context, ContextWithMutableVariables, EmptyType, FloatType, IntType, VariableMap,
 };
 
 use crate::{
@@ -346,7 +346,7 @@ impl Node {
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval(&self) -> EvalexprResult<Value> {
-        self.eval_with_context_mut(&mut ContextData::new())
+        self.eval_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into a string with an the given context.
@@ -532,21 +532,21 @@ impl Node {
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_string(&self) -> EvalexprResult<String> {
-        self.eval_string_with_context_mut(&mut ContextData::new())
+        self.eval_string_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into a float.
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_float(&self) -> EvalexprResult<FloatType> {
-        self.eval_float_with_context_mut(&mut ContextData::new())
+        self.eval_float_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into an integer.
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_int(&self) -> EvalexprResult<IntType> {
-        self.eval_int_with_context_mut(&mut ContextData::new())
+        self.eval_int_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into a float.
@@ -554,28 +554,28 @@ impl Node {
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_number(&self) -> EvalexprResult<FloatType> {
-        self.eval_number_with_context_mut(&mut ContextData::new())
+        self.eval_number_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into a boolean.
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_boolean(&self) -> EvalexprResult<bool> {
-        self.eval_boolean_with_context_mut(&mut ContextData::new())
+        self.eval_boolean_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into a tuple.
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_tuple(&self) -> EvalexprResult<TupleType> {
-        self.eval_tuple_with_context_mut(&mut ContextData::new())
+        self.eval_tuple_with_context_mut(&mut VariableMap::new())
     }
 
     /// Evaluates the operator tree rooted at this node into an empty value.
     ///
     /// Fails, if one of the operators in the expression tree fails.
     pub fn eval_empty(&self) -> EvalexprResult<EmptyType> {
-        self.eval_empty_with_context_mut(&mut ContextData::new())
+        self.eval_empty_with_context_mut(&mut VariableMap::new())
     }
 
     /// Returns the children of this node as a slice.
diff --git a/src/value/mod.rs b/src/value/mod.rs
index d598557..4e5f986 100644
--- a/src/value/mod.rs
+++ b/src/value/mod.rs
@@ -1,5 +1,11 @@
-use crate::error::{EvalexprError, EvalexprResult};
-use std::{convert::TryFrom, collections::HashMap};
+use crate::{
+    error::{EvalexprError, EvalexprResult},
+    VariableMap,
+};
+use std::{
+    collections::{BTreeMap, HashMap},
+    convert::TryFrom,
+};
 
 mod display;
 pub mod value_type;
@@ -37,7 +43,7 @@ pub enum Value {
     /// An empty value.
     Empty,
     /// Collection of key-value pairs.
-    Map(HashMap<String, Value>),
+    Map(VariableMap),
 }
 
 impl Value {
diff --git a/tests/integration.rs b/tests/integration.rs
index f43761e..82b99c0 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -110,7 +110,7 @@ fn test_boolean_examples() {
 
 #[test]
 fn test_with_context() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     context
         .set_value("tr".into(), Value::Boolean(true))
         .unwrap();
@@ -144,7 +144,7 @@ fn test_with_context() {
 
 #[test]
 fn test_functions() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     context
         .set_function(
             "sub2".to_string(),
@@ -175,7 +175,7 @@ fn test_functions() {
 
 #[test]
 fn test_n_ary_functions() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     context
         .set_function(
             "sub2".into(),
@@ -282,7 +282,7 @@ fn test_n_ary_functions() {
 
 #[test]
 fn test_capturing_functions() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     // this variable is captured by the function
     let three = 3;
     context
@@ -601,7 +601,7 @@ fn test_no_panic() {
 
 #[test]
 fn test_shortcut_functions() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     context
         .set_value("string".into(), Value::from("a string"))
         .unwrap();
@@ -1284,7 +1284,7 @@ fn test_whitespace() {
 
 #[test]
 fn test_assignment() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     assert_eq!(
         eval_empty_with_context_mut("int = 3", &mut context),
         Ok(EMPTY_VALUE)
@@ -1324,7 +1324,7 @@ fn test_assignment() {
 
 #[test]
 fn test_expression_chaining() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     assert_eq!(
         eval_int_with_context_mut("a = 5; a = a + 2; a", &mut context),
         Ok(7)
@@ -1333,7 +1333,7 @@ fn test_expression_chaining() {
 
 #[test]
 fn test_strings() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     assert_eq!(eval("\"string\""), Ok(Value::from("string")));
     assert_eq!(
         eval_with_context_mut("a = \"a string\"", &mut context),
@@ -1441,7 +1441,7 @@ fn test_implicit_context() {
 
 #[test]
 fn test_operator_assignments() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     assert_eq!(eval_empty_with_context_mut("a = 5", &mut context), Ok(()));
     assert_eq!(eval_empty_with_context_mut("a += 5", &mut context), Ok(()));
     assert_eq!(eval_empty_with_context_mut("a -= 5", &mut context), Ok(()));
@@ -1463,7 +1463,7 @@ fn test_operator_assignments() {
         Ok(())
     );
 
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     assert_eq!(eval_int_with_context_mut("a = 5; a", &mut context), Ok(5));
     assert_eq!(eval_int_with_context_mut("a += 3; a", &mut context), Ok(8));
     assert_eq!(eval_int_with_context_mut("a -= 5; a", &mut context), Ok(3));
@@ -1643,7 +1643,7 @@ fn test_hashmap_context_type_safety() {
 
 #[test]
 fn test_hashmap_context_clone_debug() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     // this variable is captured by the function
     let three = 3;
     context
@@ -2228,7 +2228,7 @@ fn assignment_lhs_is_identifier() {
     let tree = build_operator_tree("a = 1").unwrap();
     let operators: Vec<_> = tree.iter().map(|node| node.operator().clone()).collect();
 
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     tree.eval_with_context_mut(&mut context).unwrap();
     assert_eq!(context.get_value("a"), Some(&Value::Int(1)));
 
@@ -2250,7 +2250,7 @@ fn assignment_lhs_is_identifier() {
 
 #[test]
 fn test_variable_assignment_and_iteration() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     eval_with_context_mut("a = 5; b = 5.0", &mut context).unwrap();
 
     let mut variables: Vec<_> = context.iter_variables().collect();
@@ -2278,7 +2278,7 @@ fn test_negative_power() {
 
 #[test]
 fn test_builtin_functions_context() {
-    let mut context = ContextData::new();
+    let mut context = VariableMap::new();
     // Builtin functions are enabled by default for HashMapContext.
     assert_eq!(eval_with_context("max(1,3)", &context), Ok(Value::from(3)));
     // Disabling builtin function in Context.