Improved type system checks

src/core/ExpressionToRegister.go

@@ -24,17 +24,21 @@ func (f *Function) ExpressionToRegister(node *expression.Expression, register cp
 	}
 
 	if ast.IsFunctionCall(node) {
-		fn, err := f.CompileCall(node)
+		types, err := f.CompileCall(node)
+
+		if err != nil {
+			return nil, err
+		}
 
 		if register != f.CPU.Output[0] {
 			f.RegisterRegister(asm.MOVE, register, f.CPU.Output[0])
 		}
 
-		if fn == nil || len(fn.Output) == 0 {
-			return nil, err
+		if len(types) == 0 {
+			return nil, nil
 		}
 
-		return fn.Output[0].Type, err
+		return types[0], err
 	}
 
 	if node.Token.Kind == token.Array {