A Typeful Integration of SQL into Curry

Abstract

We present an extension of the declarative programming language Curry to support the access to data stored in relational databases via SQL. Since Curry is statically typed, our emphasis on this SQL integration is on type safety. Our extension respects the type system of Curry so that run-time errors due to ill-typed data are avoided. This is obtained by preprocessing SQL statements at compile time and translating them into type-safe database access operations. As a consequence, the type checker of the Curry system can spot type errors in SQL statements at compile time. To generate appropriately typed access operations, the preprocessor uses an entity-relationship (ER) model describing the structure of the relational data. In addition to standard SQL, SQL statements embedded in Curry can include program expressions and also relationships specified in the ER model. The latter feature is useful to avoid the error-prone use of foreign keys. As a result, our SQL integration supports a high-level and type-safe access to databases in Curry programs.Comment: In Proceedings WLP'15/'16/WFLP'16, arXiv:1701.0014

Fifty Years of Prolog and Beyond

“…Curry is based on the technique of narrowing, which is also the basis of other functional logic programming work (Antoy and Hanus 2010). The language has recently been used for typesafe SQL queries (Hanus and Krone 2017), for research and for teaching both the logic and the functional paradigm (Hanus 1997).…”