A Domain-Specific Language for Regular Sets of Strings and Trees

We propose a new high-level programming notation, called FIDO, that we have designed to concisely express regular sets of strings or trees. In particular, it can be viewed as a domain-speci c language for the expression of nite-state automata on large alphabets (of sometimes astronomical size). FIDO is based on a combination of mathematical logic and programming language concepts. This combination shares no similarities with usual logic programming languages. FIDO compiles into nitestate string or tree automata, so there is no concept of run-time. It has already been applied to a variety of problems of considerable complexity and practical interest. In the present paper, we motivate the need for a language like FIDO, and discuss our design and its implementation. We show how recursive data types, uni cation, implicit coercions, and subtyping can be merged with a variation of predicate logic, called the Monadic Second-order Logic (M2L) on trees. FIDO is translated rst into pure M2L via suitable encodings, and nally into nite-state automata through the MONA tool.