A Meta Lambda Calculus with Cross-Level Computation

We propose meta lambda calculus Lambda-* as a basic model of textual substitution via metavariables. The most important feature of the calculus is that every beta-redex can be reduced regardless of whether the beta-redex contains meta-level variables or not. Such a meta lambda calculus has never been achieved before due to difficulty to manage binding structure consistently with alpha-renaming in the presence of meta-level variables. We overcome the difficulty by introducing a new mechanism to deal with substitution and binding structure in a systematic way without the notion of free variables and alpha-renaming. Calculus Lambda-* enables us to investigate cross-level terms that include a certain type of level mismatch. Cross-level terms have been regarded as meaningless terms and left out of consideration thus far. We find that some cross-level terms behave as quotes and `eval' command in programming languages. With these terms, we show a procedural language as an application of the calculus, which sheds new light on the notions of stores and recursion via meta-level variables.