High-Level Views On Low-Level Representations

This paper explains how the high-level treatment of datatypes in functional languages-using features like constructor functions and pattern matching-can be made to coexist with bitdata. We use this term to describe the bit-level representations of data that are required in the construction of many different applications, including operating systems, device drivers, and assemblers. We explain our approach as a combination of two language extensions, each of which could potentially be adapted to any modem functional language. The first adds simple and elegant constructs for manipulating raw bitfield values, while the second provides a view-like mechanism for defining distinct new bitdata types with fine-control over the underlying representation. Our design leverages polymorphic type inference, as well as techniques for improvement of qualified types, to track both the type and the width of bitdata structures. We have implemented our extensions in a small functional language interpreter, and used it to show that our approach can handle a wide range of practical bitdata types.