diff --git a/src/errors.cpp b/src/errors.cpp
index 139286c..54bd83c 100644
--- a/src/errors.cpp
+++ b/src/errors.cpp
@@ -35,6 +35,7 @@ string UserError::get_message(void) const {
         case ErrorType::ModuloByZero: return "Modulo by 0";
         case ErrorType::BreakNotWithinLoop: return "Break statement not within loop";
         case ErrorType::ContinueNotWithinLoop: return "Continue statement not within loop";
+        case ErrorType::ControlReachesEndOfNonVoidFn: return "Control reaches end of non-void function";
         default: return "Unknown error type";
     }
 }
diff --git a/src/include/errors.h b/src/include/errors.h
index 04c7c5a..91438cc 100644
--- a/src/include/errors.h
+++ b/src/include/errors.h
@@ -45,6 +45,7 @@ enum class ErrorType {
     ModuloByZero,
     BreakNotWithinLoop,
     ContinueNotWithinLoop,
+    ControlReachesEndOfNonVoidFn
 };
 
 using ErrorData = variant<monostate, string>;
diff --git a/src/include/interpreter.h b/src/include/interpreter.h
index 49eff90..3f7ca87 100644
--- a/src/include/interpreter.h
+++ b/src/include/interpreter.h
@@ -25,4 +25,12 @@ public:
         : InternalError(pos) {}
 };
 
+class ReturnException : public InternalError {
+public:
+    EvalResult val;
+
+    explicit ReturnException(EvalResult val)
+        : InternalError(), val(val) {}
+};
+
 #endif
\ No newline at end of file
diff --git a/src/include/memory.h b/src/include/memory.h
index 0f56a75..5175fc5 100644
--- a/src/include/memory.h
+++ b/src/include/memory.h
@@ -17,7 +17,7 @@ class Memory {
 
         MemoryVar& get(string identifier);
         Scope& get_function_scope(void);
-        void declare(string identifier, Type type, CodePosition pos);
+        void declare(string identifier, Type type, CodePosition pos = { });
         void update(string identifier, EvalResult value);
 
         Scope& _debug_top(void);
diff --git a/src/interpreter.cpp b/src/interpreter.cpp
index 84107ef..5c30bb4 100644
--- a/src/interpreter.cpp
+++ b/src/interpreter.cpp
@@ -42,6 +42,16 @@ double double_cast(EvalResult value) {
     }
 }
 
+EvalResult cast_from_type(Type type, EvalResult val) {
+    switch (type.type) {
+        case TypeType::Int: return int_cast(val);
+        case TypeType::Double: return double_cast(val);
+        case TypeType::Void: return {};
+        default:
+            throw exception();
+    }
+}
+
 EvalResult eval(Node &ast, Memory &memory) {
     if (holds_alternative<InnerNode>(ast)) {
         InnerNode node = get<InnerNode>(ast);
@@ -139,12 +149,12 @@ EvalResult eval(Node &ast, Memory &memory) {
             } break;
             case NodeType::FunctionPrototype: {
                 Token retTypeTok = get<Token>(node.children[0]);
-                Token fnIdentifierTok = get<Token>(node.children[1]);
-                string fnIdentifier = get<string>(fnIdentifierTok.data);
+                Token identifierTok = get<Token>(node.children[1]);
+                string identifier = get<string>(identifierTok.data);
 
                 FunctionPrototype prototype = make_fn_prototype(node);
 
-                memory.declare(fnIdentifier, {
+                memory.declare(identifier, {
                     .type = TypeType::Function,
                     .data = prototype
                 }, retTypeTok.pos);
@@ -153,25 +163,61 @@ EvalResult eval(Node &ast, Memory &memory) {
             } break;
             case NodeType::FunctionDeclaration: {
                 Token retTypeTok = get<Token>(node.children[0]);
-                Token fnIdentifierTok = get<Token>(node.children[1]);
-                string fnIdentifier = get<string>(fnIdentifierTok.data);
+                Token identifierTok = get<Token>(node.children[1]);
+                string identifier = get<string>(identifierTok.data);
 
                 FunctionPrototype prototype = make_fn_prototype(node);
 
-                memory.declare(fnIdentifier, {
+                memory.declare(identifier, {
                     .type = TypeType::Function,
                     .data = prototype
                 }, retTypeTok.pos);
 
-                memory.update(fnIdentifier, node.children[3]);
+                memory.update(identifier, node.children[3]);
 
                 return {};
             } break;
             case NodeType::FunctionCall: {
-                memory.add_scope(ScopeType::Function);
+                Token identifierTok = get<Token>(node.children[0]);
+                string identifier = get<string>(identifierTok.data);
+                vector<Node> args = get<InnerNode>(node.children[1]).children;
+
+                MemoryVar& var = memory.get(identifier);
+
+                if (!var.initialized)
+                    throw RuntimeError(ErrorType::UninitializedIdentifier, identifierTok.pos, identifier);
+
+                vector<EvalResult> argValues = {};
+                for (Node arg : args) {
+                    argValues.push_back(eval(arg, memory));
+                }
+
+                FunctionPrototype prototype = get<FunctionPrototype>(var.type.data);
+
+                EvalResult res = {};
+
+                memory.add_scope(ScopeType::Function, identifierTok.pos, &var);
 
                 try {
-                    
+                    for (size_t i = 1; i < prototype.size(); i++) {
+                        tuple<Type, string> argDef = prototype[i];
+                        Type argType = get<0>(argDef);
+                        string argName = get<1>(argDef); 
+                        memory.declare(argName, argType);
+                        memory.update(argName, cast_from_type(argType, argValues[i - 1]));
+                    }
+
+                    try {
+                        eval(get<Node>(var.value), memory);
+
+                        // Tmp: no flow control
+                        if (get<0>(prototype[0]).type != TypeType::Void) {
+                            throw RuntimeError(ErrorType::ControlReachesEndOfNonVoidFn, identifierTok.pos);
+                        }
+                    }
+                    catch (const ReturnException& e) {
+                        res = e.val;
+                    }
 
                     memory.remove_scope();
                 }
@@ -181,6 +227,11 @@ EvalResult eval(Node &ast, Memory &memory) {
                     exception_ptr e = current_exception();
                     if (e) rethrow_exception(e);
                 }
+
+                return cast_from_type(get<0>(prototype[0]), res);
+            } break;
+            case NodeType::Return: {
+                throw ReturnException(eval(node.children[0], memory));
             } break;
             case NodeType::Eq: {
                 EvalResult e1 = eval(node.children[0], memory);
diff --git a/src/memory.cpp b/src/memory.cpp
index 053bd00..bb6c306 100644
--- a/src/memory.cpp
+++ b/src/memory.cpp
@@ -50,6 +50,7 @@ Scope& Memory::get_function_scope(void) {
         if (scope.type == ScopeType::Function) return scope;
     }
     
+    // Tmp: no flow control
     throw InternalError();
 }