diff --git a/src/context/mod.rs b/src/context/mod.rs
index d79cd4e..8cff836 100644
--- a/src/context/mod.rs
+++ b/src/context/mod.rs
@@ -1,33 +1,50 @@
+//! A context defines methods to retrieve variable values and call functions for literals in an expression tree.
+//! If mutable, it also allows to assign to variables.
+//!
+//! 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;
 
 use crate::{function::Function, value::value_type::ValueType, EvalexprError, EvalexprResult};
 
 use crate::value::Value;
 
-/// A mutable context for an expression tree.
-///
-/// A context defines methods to retrieve values and functions for literals in an expression tree.
-/// In addition, it also allows the manipulation of values and functions.
-/// 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.
+/// An immutable context.
 pub trait Context {
     /// Returns the value that is linked to the given identifier.
     fn get_value(&self, identifier: &str) -> Option<&Value>;
 
-    /// Returns the function that is linked to the given identifier.
-    fn get_function(&self, identifier: &str) -> Option<&Function>;
+    /// Calls the function that is linked to the given identifier with the given argument.
+    /// If no function with the given identifier is found, this method returns `EvalexprError::FunctionIdentifierNotFound`.
+    fn call_function(&self, identifier: &str, argument: &Value) -> EvalexprResult<Value>;
+}
 
-    /// Links the given value to the given identifier.
+/// 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<()> {
-        Err(EvalexprError::ContextNotManipulable)
-    }
-
-    /// Links the given function to the given identifier.
-    fn set_function(&mut self, _identifier: String, _function: Function) -> EvalexprResult<()> {
-        Err(EvalexprError::ContextNotManipulable)
+        Err(EvalexprError::ContextNotMutable)
     }
 }
 
+/// A context that allows to assign to function identifiers.
+pub trait ContextWithMutableFunctions: Context {
+    /// Sets the function with the given identifier to the given function.
+    fn set_function(&mut self, _identifier: String, _function: Function) -> EvalexprResult<()> {
+        Err(EvalexprError::ContextNotMutable)
+    }
+}
+
+/*/// A context that allows to retrieve functions programmatically.
+pub trait GetFunctionContext: Context {
+    /// Returns the function that is linked to the given identifier.
+    ///
+    /// This might not be possible for all functions, as some might be hard-coded.
+    /// In this case, a special error variant should be returned (Not yet implemented).
+    fn get_function(&self, identifier: &str) -> Option<&Function>;
+}*/
+
 /// A context that returns `None` for each identifier.
 pub struct EmptyContext;
 
@@ -36,8 +53,10 @@ impl Context for EmptyContext {
         None
     }
 
-    fn get_function(&self, _identifier: &str) -> Option<&Function> {
-        None
+    fn call_function(&self, identifier: &str, _argument: &Value) -> EvalexprResult<Value> {
+        Err(EvalexprError::FunctionIdentifierNotFound(
+            identifier.to_string(),
+        ))
     }
 }
 
@@ -66,10 +85,18 @@ impl Context for HashMapContext {
         self.variables.get(identifier)
     }
 
-    fn get_function(&self, identifier: &str) -> Option<&Function> {
-        self.functions.get(identifier)
+    fn call_function(&self, identifier: &str, argument: &Value) -> EvalexprResult<Value> {
+        if let Some(function) = self.functions.get(identifier) {
+            function.call(argument)
+        } else {
+            Err(EvalexprError::FunctionIdentifierNotFound(
+                identifier.to_string(),
+            ))
+        }
     }
+}
 
+impl ContextWithMutableVariables for HashMapContext {
     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) {
@@ -84,7 +111,9 @@ impl Context for HashMapContext {
         self.variables.insert(identifier, value);
         Ok(())
     }
+}
 
+impl ContextWithMutableFunctions for HashMapContext {
     fn set_function(&mut self, identifier: String, function: Function) -> EvalexprResult<()> {
         self.functions.insert(identifier, function);
         Ok(())
diff --git a/src/error/display.rs b/src/error/display.rs
index 47f4993..3de998f 100644
--- a/src/error/display.rs
+++ b/src/error/display.rs
@@ -106,7 +106,7 @@ impl fmt::Display for EvalexprError {
                 "Regular expression {:?} is invalid: {:?}",
                 regex, message
             ),
-            ContextNotManipulable => write!(f, "Cannot manipulate context"),
+            ContextNotMutable => write!(f, "Cannot manipulate context"),
             IllegalEscapeSequence(string) => write!(f, "Illegal escape sequence: {}", string),
             CustomMessage(message) => write!(f, "Error: {}", message),
         }
diff --git a/src/error/mod.rs b/src/error/mod.rs
index cf008a3..5c1a0df 100644
--- a/src/error/mod.rs
+++ b/src/error/mod.rs
@@ -191,7 +191,7 @@ pub enum EvalexprError {
     },
 
     /// A modification was attempted on a `Context` that does not allow modifications.
-    ContextNotManipulable,
+    ContextNotMutable,
 
     /// An escape sequence within a string literal is illegal.
     IllegalEscapeSequence(String),
diff --git a/src/interface/mod.rs b/src/interface/mod.rs
index 73dfefa..9147d2c 100644
--- a/src/interface/mod.rs
+++ b/src/interface/mod.rs
@@ -1,6 +1,6 @@
 use crate::{
-    token, tree, value::TupleType, Context, EmptyType, EvalexprError, EvalexprResult, FloatType,
-    HashMapContext, IntType, Node, Value, EMPTY_VALUE,
+    token, tree, value::TupleType, Context, ContextWithMutableVariables, EmptyType, EvalexprError,
+    EvalexprResult, FloatType, HashMapContext, IntType, Node, Value, EMPTY_VALUE,
 };
 
 /// Evaluate the given expression string.
@@ -33,7 +33,7 @@ pub fn eval(string: &str) -> EvalexprResult<Value> {
 /// ```
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_with_context(string: &str, context: &dyn Context) -> EvalexprResult<Value> {
+pub fn eval_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<Value> {
     tree::tokens_to_operator_tree(token::tokenize(string)?)?.eval_with_context(context)
 }
 
@@ -52,7 +52,10 @@ pub fn eval_with_context(string: &str, context: &dyn Context) -> EvalexprResult<
 /// ```
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_with_context_mut(string: &str, context: &mut dyn Context) -> EvalexprResult<Value> {
+pub fn eval_with_context_mut<C: ContextWithMutableVariables>(
+    string: &str,
+    context: &mut C,
+) -> EvalexprResult<Value> {
     tree::tokens_to_operator_tree(token::tokenize(string)?)?.eval_with_context_mut(context)
 }
 
@@ -137,7 +140,7 @@ pub fn eval_empty(string: &str) -> EvalexprResult<EmptyType> {
 /// Evaluate the given expression string into a string with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_string_with_context(string: &str, context: &dyn Context) -> EvalexprResult<String> {
+pub fn eval_string_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<String> {
     match eval_with_context(string, context) {
         Ok(Value::String(string)) => Ok(string),
         Ok(value) => Err(EvalexprError::expected_string(value)),
@@ -148,7 +151,7 @@ pub fn eval_string_with_context(string: &str, context: &dyn Context) -> Evalexpr
 /// Evaluate the given expression string into an integer with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_int_with_context(string: &str, context: &dyn Context) -> EvalexprResult<IntType> {
+pub fn eval_int_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<IntType> {
     match eval_with_context(string, context) {
         Ok(Value::Int(int)) => Ok(int),
         Ok(value) => Err(EvalexprError::expected_int(value)),
@@ -159,7 +162,7 @@ pub fn eval_int_with_context(string: &str, context: &dyn Context) -> EvalexprRes
 /// Evaluate the given expression string into a float with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_float_with_context(string: &str, context: &dyn Context) -> EvalexprResult<FloatType> {
+pub fn eval_float_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<FloatType> {
     match eval_with_context(string, context) {
         Ok(Value::Float(float)) => Ok(float),
         Ok(value) => Err(EvalexprError::expected_float(value)),
@@ -171,7 +174,10 @@ pub fn eval_float_with_context(string: &str, context: &dyn Context) -> EvalexprR
 /// If the result of the expression is an integer, it is silently converted into a float.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_number_with_context(string: &str, context: &dyn Context) -> EvalexprResult<FloatType> {
+pub fn eval_number_with_context<C: Context>(
+    string: &str,
+    context: &C,
+) -> EvalexprResult<FloatType> {
     match eval_with_context(string, context) {
         Ok(Value::Float(float)) => Ok(float),
         Ok(Value::Int(int)) => Ok(int as FloatType),
@@ -183,7 +189,7 @@ pub fn eval_number_with_context(string: &str, context: &dyn Context) -> Evalexpr
 /// Evaluate the given expression string into a boolean with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_boolean_with_context(string: &str, context: &dyn Context) -> EvalexprResult<bool> {
+pub fn eval_boolean_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<bool> {
     match eval_with_context(string, context) {
         Ok(Value::Boolean(boolean)) => Ok(boolean),
         Ok(value) => Err(EvalexprError::expected_boolean(value)),
@@ -194,7 +200,7 @@ pub fn eval_boolean_with_context(string: &str, context: &dyn Context) -> Evalexp
 /// Evaluate the given expression string into a tuple with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_tuple_with_context(string: &str, context: &dyn Context) -> EvalexprResult<TupleType> {
+pub fn eval_tuple_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<TupleType> {
     match eval_with_context(string, context) {
         Ok(Value::Tuple(tuple)) => Ok(tuple),
         Ok(value) => Err(EvalexprError::expected_tuple(value)),
@@ -205,7 +211,7 @@ pub fn eval_tuple_with_context(string: &str, context: &dyn Context) -> EvalexprR
 /// Evaluate the given expression string into an empty value with the given context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_empty_with_context(string: &str, context: &dyn Context) -> EvalexprResult<EmptyType> {
+pub fn eval_empty_with_context<C: Context>(string: &str, context: &C) -> EvalexprResult<EmptyType> {
     match eval_with_context(string, context) {
         Ok(Value::Empty) => Ok(EMPTY_VALUE),
         Ok(value) => Err(EvalexprError::expected_empty(value)),
@@ -216,9 +222,9 @@ pub fn eval_empty_with_context(string: &str, context: &dyn Context) -> EvalexprR
 /// Evaluate the given expression string into a string with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_string_with_context_mut(
+pub fn eval_string_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<String> {
     match eval_with_context_mut(string, context) {
         Ok(Value::String(string)) => Ok(string),
@@ -230,9 +236,9 @@ pub fn eval_string_with_context_mut(
 /// Evaluate the given expression string into an integer with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_int_with_context_mut(
+pub fn eval_int_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<IntType> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Int(int)) => Ok(int),
@@ -244,9 +250,9 @@ pub fn eval_int_with_context_mut(
 /// Evaluate the given expression string into a float with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_float_with_context_mut(
+pub fn eval_float_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<FloatType> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Float(float)) => Ok(float),
@@ -259,9 +265,9 @@ pub fn eval_float_with_context_mut(
 /// If the result of the expression is an integer, it is silently converted into a float.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_number_with_context_mut(
+pub fn eval_number_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<FloatType> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Float(float)) => Ok(float),
@@ -274,9 +280,9 @@ pub fn eval_number_with_context_mut(
 /// Evaluate the given expression string into a boolean with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_boolean_with_context_mut(
+pub fn eval_boolean_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<bool> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Boolean(boolean)) => Ok(boolean),
@@ -288,9 +294,9 @@ pub fn eval_boolean_with_context_mut(
 /// Evaluate the given expression string into a tuple with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_tuple_with_context_mut(
+pub fn eval_tuple_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<TupleType> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Tuple(tuple)) => Ok(tuple),
@@ -302,9 +308,9 @@ pub fn eval_tuple_with_context_mut(
 /// Evaluate the given expression string into an empty value with the given mutable context.
 ///
 /// *See the [crate doc](index.html) for more examples and explanations of the expression format.*
-pub fn eval_empty_with_context_mut(
+pub fn eval_empty_with_context_mut<C: ContextWithMutableVariables>(
     string: &str,
-    context: &mut dyn Context,
+    context: &mut C,
 ) -> EvalexprResult<EmptyType> {
     match eval_with_context_mut(string, context) {
         Ok(Value::Empty) => Ok(EMPTY_VALUE),
diff --git a/src/lib.rs b/src/lib.rs
index f86ffc9..b9c48a3 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -196,7 +196,7 @@
 //! use evalexpr::*;
 //!
 //! let mut context = HashMapContext::new();
-//! assert_eq!(eval_with_context("a = 5", &context), Err(EvalexprError::ContextNotManipulable));
+//! assert_eq!(eval_with_context("a = 5", &context), Err(EvalexprError::ContextNotMutable));
 //! assert_eq!(eval_empty_with_context_mut("a = 5", &mut context), Ok(EMPTY_VALUE));
 //! assert_eq!(eval_empty_with_context_mut("a = 5.0", &mut context),
 //!            Err(EvalexprError::expected_int(5.0.into())));
@@ -259,7 +259,7 @@
 //! let mut context = HashMapContext::new();
 //! assert_eq!(eval_with_context_mut("a = 5;", &mut context), Ok(Value::from(())));
 //! // Assignments require mutable contexts
-//! assert_eq!(eval_with_context("a = 6", &context), Err(EvalexprError::ContextNotManipulable));
+//! assert_eq!(eval_with_context("a = 6", &context), Err(EvalexprError::ContextNotMutable));
 //! // The HashMapContext is type safe
 //! assert_eq!(eval_with_context_mut("a = 5.5", &mut context),
 //!            Err(EvalexprError::ExpectedInt { actual: Value::from(5.5) }));
@@ -488,7 +488,10 @@ extern crate serde;
 extern crate serde_derive;
 
 pub use crate::{
-    context::{Context, EmptyContext, HashMapContext},
+    context::{
+        Context, ContextWithMutableFunctions, ContextWithMutableVariables, EmptyContext,
+        HashMapContext,
+    },
     error::{EvalexprError, EvalexprResult},
     function::Function,
     interface::*,
diff --git a/src/operator/mod.rs b/src/operator/mod.rs
index e4cf713..95c64e4 100644
--- a/src/operator/mod.rs
+++ b/src/operator/mod.rs
@@ -1,6 +1,6 @@
 use crate::function::builtin::builtin_function;
 
-use crate::{context::Context, error::*, value::Value};
+use crate::{context::Context, error::*, value::Value, ContextWithMutableVariables};
 use std::borrow::Borrow;
 
 mod display;
@@ -169,7 +169,11 @@ impl Operator {
     }
 
     /// Evaluates the operator with the given arguments and context.
-    pub(crate) fn eval(&self, arguments: &[Value], context: &dyn Context) -> EvalexprResult<Value> {
+    pub(crate) fn eval<C: Context>(
+        &self,
+        arguments: &[Value],
+        context: &C,
+    ) -> EvalexprResult<Value> {
         use crate::operator::Operator::*;
         match self {
             RootNode => {
@@ -408,7 +412,7 @@ impl Operator {
                 Ok(Value::Boolean(!a))
             },
             Assign | AddAssign | SubAssign | MulAssign | DivAssign | ModAssign | ExpAssign
-            | AndAssign | OrAssign => Err(EvalexprError::ContextNotManipulable),
+            | AndAssign | OrAssign => Err(EvalexprError::ContextNotMutable),
             Tuple => Ok(Value::Tuple(arguments.into())),
             Chain => {
                 if arguments.is_empty() {
@@ -437,24 +441,27 @@ impl Operator {
                 expect_operator_argument_amount(arguments.len(), 1)?;
                 let arguments = &arguments[0];
 
-                if let Some(function) = context.get_function(&identifier) {
-                    function.call(arguments)
-                } else if let Some(builtin_function) = builtin_function(&identifier) {
-                    builtin_function.call(arguments)
-                } else {
-                    Err(EvalexprError::FunctionIdentifierNotFound(
-                        identifier.clone(),
-                    ))
+                match context.call_function(&identifier, arguments) {
+                    Err(EvalexprError::FunctionIdentifierNotFound(_)) => {
+                        if let Some(builtin_function) = builtin_function(&identifier) {
+                            builtin_function.call(arguments)
+                        } else {
+                            Err(EvalexprError::FunctionIdentifierNotFound(
+                                identifier.clone(),
+                            ))
+                        }
+                    },
+                    result => result,
                 }
             },
         }
     }
 
     /// Evaluates the operator with the given arguments and mutable context.
-    pub(crate) fn eval_mut(
+    pub(crate) fn eval_mut<C: ContextWithMutableVariables>(
         &self,
         arguments: &[Value],
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<Value> {
         use crate::operator::Operator::*;
         match self {
diff --git a/src/tree/mod.rs b/src/tree/mod.rs
index e128312..d5f2527 100644
--- a/src/tree/mod.rs
+++ b/src/tree/mod.rs
@@ -1,11 +1,10 @@
 use crate::{
     token::Token,
     value::{TupleType, EMPTY_VALUE},
-    EmptyType, FloatType, HashMapContext, IntType,
+    Context, ContextWithMutableVariables, EmptyType, FloatType, HashMapContext, IntType,
 };
 
 use crate::{
-    context::Context,
     error::{EvalexprError, EvalexprResult},
     operator::*,
     value::Value,
@@ -119,7 +118,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node with the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_with_context(&self, context: &dyn Context) -> EvalexprResult<Value> {
+    pub fn eval_with_context<C: Context>(&self, context: &C) -> EvalexprResult<Value> {
         let mut arguments = Vec::new();
         for child in self.children() {
             arguments.push(child.eval_with_context(context)?);
@@ -130,7 +129,10 @@ impl Node {
     /// Evaluates the operator tree rooted at this node with the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_with_context_mut(&self, context: &mut dyn Context) -> EvalexprResult<Value> {
+    pub fn eval_with_context_mut<C: ContextWithMutableVariables>(
+        &self,
+        context: &mut C,
+    ) -> EvalexprResult<Value> {
         let mut arguments = Vec::new();
         for child in self.children() {
             arguments.push(child.eval_with_context_mut(context)?);
@@ -148,7 +150,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a string with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_string_with_context(&self, context: &dyn Context) -> EvalexprResult<String> {
+    pub fn eval_string_with_context<C: Context>(&self, context: &C) -> EvalexprResult<String> {
         match self.eval_with_context(context) {
             Ok(Value::String(string)) => Ok(string),
             Ok(value) => Err(EvalexprError::expected_string(value)),
@@ -159,7 +161,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a float with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_float_with_context(&self, context: &dyn Context) -> EvalexprResult<FloatType> {
+    pub fn eval_float_with_context<C: Context>(&self, context: &C) -> EvalexprResult<FloatType> {
         match self.eval_with_context(context) {
             Ok(Value::Float(float)) => Ok(float),
             Ok(value) => Err(EvalexprError::expected_float(value)),
@@ -170,7 +172,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into an integer with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_int_with_context(&self, context: &dyn Context) -> EvalexprResult<IntType> {
+    pub fn eval_int_with_context<C: Context>(&self, context: &C) -> EvalexprResult<IntType> {
         match self.eval_with_context(context) {
             Ok(Value::Int(int)) => Ok(int),
             Ok(value) => Err(EvalexprError::expected_int(value)),
@@ -182,7 +184,7 @@ impl Node {
     /// If the result of the expression is an integer, it is silently converted into a float.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_number_with_context(&self, context: &dyn Context) -> EvalexprResult<FloatType> {
+    pub fn eval_number_with_context<C: Context>(&self, context: &C) -> EvalexprResult<FloatType> {
         match self.eval_with_context(context) {
             Ok(Value::Int(int)) => Ok(int as FloatType),
             Ok(Value::Float(float)) => Ok(float),
@@ -194,7 +196,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a boolean with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_boolean_with_context(&self, context: &dyn Context) -> EvalexprResult<bool> {
+    pub fn eval_boolean_with_context<C: Context>(&self, context: &C) -> EvalexprResult<bool> {
         match self.eval_with_context(context) {
             Ok(Value::Boolean(boolean)) => Ok(boolean),
             Ok(value) => Err(EvalexprError::expected_boolean(value)),
@@ -205,7 +207,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a tuple with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_tuple_with_context(&self, context: &dyn Context) -> EvalexprResult<TupleType> {
+    pub fn eval_tuple_with_context<C: Context>(&self, context: &C) -> EvalexprResult<TupleType> {
         match self.eval_with_context(context) {
             Ok(Value::Tuple(tuple)) => Ok(tuple),
             Ok(value) => Err(EvalexprError::expected_tuple(value)),
@@ -216,7 +218,7 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into an empty value with an the given context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_empty_with_context(&self, context: &dyn Context) -> EvalexprResult<EmptyType> {
+    pub fn eval_empty_with_context<C: Context>(&self, context: &C) -> EvalexprResult<EmptyType> {
         match self.eval_with_context(context) {
             Ok(Value::Empty) => Ok(EMPTY_VALUE),
             Ok(value) => Err(EvalexprError::expected_empty(value)),
@@ -227,9 +229,9 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a string with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_string_with_context_mut(
+    pub fn eval_string_with_context_mut<C: ContextWithMutableVariables>(
         &self,
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<String> {
         match self.eval_with_context_mut(context) {
             Ok(Value::String(string)) => Ok(string),
@@ -241,9 +243,9 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a float with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_float_with_context_mut(
+    pub fn eval_float_with_context_mut<C: ContextWithMutableVariables>(
         &self,
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<FloatType> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Float(float)) => Ok(float),
@@ -255,7 +257,10 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into an integer with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_int_with_context_mut(&self, context: &mut dyn Context) -> EvalexprResult<IntType> {
+    pub fn eval_int_with_context_mut<C: ContextWithMutableVariables>(
+        &self,
+        context: &mut C,
+    ) -> EvalexprResult<IntType> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Int(int)) => Ok(int),
             Ok(value) => Err(EvalexprError::expected_int(value)),
@@ -267,9 +272,9 @@ impl Node {
     /// If the result of the expression is an integer, it is silently converted into a float.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_number_with_context_mut(
+    pub fn eval_number_with_context_mut<C: ContextWithMutableVariables>(
         &self,
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<FloatType> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Int(int)) => Ok(int as FloatType),
@@ -282,7 +287,10 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a boolean with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_boolean_with_context_mut(&self, context: &mut dyn Context) -> EvalexprResult<bool> {
+    pub fn eval_boolean_with_context_mut<C: ContextWithMutableVariables>(
+        &self,
+        context: &mut C,
+    ) -> EvalexprResult<bool> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Boolean(boolean)) => Ok(boolean),
             Ok(value) => Err(EvalexprError::expected_boolean(value)),
@@ -293,9 +301,9 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into a tuple with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_tuple_with_context_mut(
+    pub fn eval_tuple_with_context_mut<C: ContextWithMutableVariables>(
         &self,
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<TupleType> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Tuple(tuple)) => Ok(tuple),
@@ -307,9 +315,9 @@ impl Node {
     /// Evaluates the operator tree rooted at this node into an empty value with an the given mutable context.
     ///
     /// Fails, if one of the operators in the expression tree fails.
-    pub fn eval_empty_with_context_mut(
+    pub fn eval_empty_with_context_mut<C: ContextWithMutableVariables>(
         &self,
-        context: &mut dyn Context,
+        context: &mut C,
     ) -> EvalexprResult<EmptyType> {
         match self.eval_with_context_mut(context) {
             Ok(Value::Empty) => Ok(EMPTY_VALUE),