Translating Specifications in a Dependently Typed Lambda Calculus into a Predicate Logic Form

Dependently typed lambda calculi such as the Edinburgh Logical Framework (LF) are a popular means for encoding rule-based specifications concerning formal syntactic objects. In these frameworks, relations over terms representing formal objects are naturally captured by making use of the dependent structure of types. We consider here the meaning-preserving translation of specifications written in this style into a predicate logic over simply typed λ-terms. Such a translation can provide the basis for efficient implementation and sophisticated capabilities for reasoning about specifications. We start with a previously described translation of LF specifications to formulas in the logic of higher-order hereditary Harrop (hohh) formulas. We show how this translation can be improved by recognizing and eliminating redundant type checking information contained in it. This benefits both the clarity of translated formulas, and reduces the effort which must be spent on type checking during execution. To allow this translation to be used to execute LF specifications, we describe an inverse transformation from hohhterms to LF expressions; thus computations can be carried out using the translated form and the results can then be exported back into LF. Execution based on LF specifications may also involve some forms of type reconstruction. We discuss the possibility of supporting such a capability using the translation under some reasonable restrictions on the structure of specifications.