Language and program design for functional dependencies

Abstract

Eight years ago, functional dependencies, a concept from the theory of relational databases, were proposed as a mechanism for avoiding common problems with multiple parameter type classes in Haskell. In this context, functional dependencies give programmers a means to specify the semantics of a type class more precisely, and to obtain more accurate inferred types as a result. As time passed, however, several issues were uncovered - both in the design of a language to support functional dependencies, and in the ways that programmers use them - that led some to search for new, better alternatives.