Dependent types reflect the fact that validity of data is often a relative notion by allowing prior data to affect the types of subsequent data. Not only does this make for a precise type system, but also a highly generic one: both the type and the program for each instance of a family of operations can be computed from the data which codes for that instance. Recent experimental extensions to the Haskell type class mechanism give us strong tools to relativize types to other types. We may simulate some aspects of dependent typing by making counterfeit type-level copies of data, with type constructors simulating data constructors and type classes simulating datatypes. This paper gives examples of the technique and discusses its potential. 1

Abstract. It is commonly believed that in dependently typed programming languages, the blurring of the distinction between types and values means that no type erasure is possible at run-time. In this paper, however, we propose an alternative phase distinction. Rather than distinguishing types and values in the compilation of EPIGRAM, we distinguish compile-time and run-time evaluation, and show by a series of program transformations that values which are not required at run-time can be erased. 1

1.1 An overview of the specification language Gallina.................... 5