Greg Meredith
Here is an idea so obvious that someone else must have already thought of it and worked it all out. Consider the following grammar.
Hello! If I understand your basic idea correctly, it is to split a recursive data type into two parts, a non-recursive type constructor and a knot-tying recursive type. This idea has been christened "two-level types" by Tim Sheard and Emir Pasalic. 2004. Two-level types and parameterized modules. Journal of Functional Programming 14(5):547-587. The idea dates earlier, to initial-algebra semantics and "functional programming with bananas and lenses": Mark P. Jones. 1995. Functional programming with overloading and higher-order polymorphism. In Advanced functional programming: 1st international spring school on advanced functional programming techniques, ed. Johan Jeuring and Erik Meijer, 97-136. Lecture Notes in Computer Science 925. http://web.cecs.pdx.edu/~mpj/pubs/springschool.html Erik Meijer, Maarten Fokkinga, and Ross Paterson. 1991. Functional programming with bananas, lenses, envelopes and barbed wire. In Functional programming languages and computer architecture: 5th conference, ed. John Hughes, 124-144. Lecture Notes in Computer Science 523. http://research.microsoft.com/~emeijer/Papers/fpca91.pdf Cheers, Ken -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig Nevertheless, most cosmologists, including Dr. Guth and Dr. Linde, agree that the universe ultimately must come from somewhere, and that nothing is the leading candidate. Dennis Overbye, New York Times, May 22, 2001.