diff --git a/src/analysis.cpp b/src/analysis.cpp
index b2bebc9..687991b 100644
--- a/src/analysis.cpp
+++ b/src/analysis.cpp
@@ -264,6 +264,55 @@ AnalysisResult analyze(Node &ast, Memory &memory) {
                 analyze(node.children[0], memory);
                 return analyze(node.children[1], memory);
             }
+            case NodeType::FunctionPrototype: {
+                Token return_type_token = get<Token>(node.children[0]);
+                string return_type_string = get<string>(return_type_token.data);
+                Type return_type = try_string_to_type(return_type_string, return_type_token.pos);
+
+                Token token = get<Token>(node.children[1]);
+                string function_name = get<string>(token.data);
+
+                try {
+                    memory.get_function_scope();
+                    throw RuntimeError(ErrorType::NestedFunction, token.pos, {});
+                } catch (const InternalError& _) {}
+
+                memory.declare(function_name, {
+                    .type = TypeType::Function,
+                    .data = make_fn_prototype(node)
+                }, return_type_token.pos);
+
+                return {};
+            } break;
+            case NodeType::FunctionDeclaration: {
+                Token return_type_token = get<Token>(node.children[0]);
+                string return_type_string = get<string>(return_type_token.data);
+                Type return_type = try_string_to_type(return_type_string, return_type_token.pos);
+
+                Token token = get<Token>(node.children[1]);
+                string function_name = get<string>(token.data);
+
+                try {
+                    memory.get_function_scope();
+                    throw RuntimeError(ErrorType::NestedFunction, token.pos, {});
+                } catch (const InternalError& _) {}
+
+                if (memory.contains(function_name) && memory.get(function_name).initialized)
+                    throw RuntimeError(ErrorType::FunctionRedefinition, token.pos, function_name);
+
+                memory.declare(function_name, {
+                    .type = TypeType::Function,
+                    .data = make_fn_prototype(node)
+                }, return_type_token.pos);
+
+                memory.update(function_name, node.children[3]);
+
+                memory.add_scope(ScopeType::Function, token.pos, &memory.get(function_name));
+                analyze(node.children[3], memory);
+                memory.remove_scope();
+
+                return {};
+            } break;
             default:
                 return {};
         }
diff --git a/src/errors.cpp b/src/errors.cpp
index ba55fd2..e0a1f22 100644
--- a/src/errors.cpp
+++ b/src/errors.cpp
@@ -25,6 +25,7 @@ string UserError::get_message(void) const {
         case ErrorType::TypesNotComparable: return "Types not comparable";
         case ErrorType::ExpectedIntegralType: return "Expression must have integral type";
         case ErrorType::NestedFunction: return "Function definition is not allowed here";
+        case ErrorType::FunctionRedefinition: return "Redefinition of '"+get<string>(this->data)+"'";
         case ErrorType::ExpectedArithmeticType: return "Expression must have arithmetic type";
         case ErrorType::UnknownIdentifier: return "Unknown identifier '"+get<string>(this->data)+"'";
         case ErrorType::AlreadyDeclaredIdentifier: return "Already declared identifier '"+get<string>(this->data)+"'";
diff --git a/src/include/errors.h b/src/include/errors.h
index 4f0f54e..b30abdb 100644
--- a/src/include/errors.h
+++ b/src/include/errors.h
@@ -34,6 +34,7 @@ enum class ErrorType {
     ExpectedIntegralType,
     ExpectedArithmeticType,
     NestedFunction,
+    FunctionRedefinition,
 
     // Runtime
     UnknownIdentifier,