From the viewpoint of adaptability, we classify software systems as being nonreflexive, introspective and adaptive. Introducing a simple example of LL(1) languages for expressions, we present its nonreflexive and adaptive implementation using Haskell functional language. Multiple metalevel concepts are an essential demand for a systematic language approach, to build up adaptable software systems dynamically, i.e. to evolve them. A feedback reflection loop from data to code through metalevel data is the basic implementation requirement and the proposition for semi-automatic evolution of software systems. In this sense, practical experiment introduced in this paper is related to the base level of language, but it illustrates the ability for extensions primarily in horizontal but also in vertical direction of an adaptive system.