Type Classes with Functional Dependencies

摘要: Type classes in Haskell allow programmers to define functions that can be used on a set of different types, with potentially implementation each case. For example, type are support equality and numeric for monadic programming. A commonly requested extension 'multiple parameters' allows more general interpretation as relations has many useful applications. Unfortunately, these examples do not work well practice, leading ambiguities inaccuracies inferred types delaying the detection errors. This paper illustrates kind problems occur multiple parameter classes, explains how they resolved by allowing specify explicit dependencies between parameters. particular novelty this is application ideas from theory relational databases design systems.