Multi-tier programming?

Kalen Delaney recently passed on some interesting details about a conversation she had with Phil Wadler, an academian in Edinburgh. Phil has proposed a new language called Links that brings together front-end client programming, middle-tier programming, and back-end programming.  Details and some demos for the language proposal are available at

Here is an overview:


e-Commerce, e-Government, e-Science --- the coining of such words reflects the growing importance of the World Wide Web in all aspects of our lives. Consumer spending on the web in Britain exceeds 12 billion pounds a year.

A typical web program involves three tiers. The front-end is the browser running on your computer. The middle-tier is a server, executing the logic that controls your interaction with the web site. The back-end is a database, providing the information you wish to access, such as a catalog of items for purchase, a collection of government records, or a store of scientific data.

The programmer must master a myriad of languages: the logic is written in a mixture of Java, Python, and Perl; the forms in HTML, XML, and Javascript; and the queries are written in SQL or XQuery. There is no easy way to link these --- to be sure that a form in HTML or a query in SQL produces data of a type that the logic in Java expects. This is called the impedance mismatch problem.

Links will solve the impedance mismatch problem by providing a single language for all three tiers. The system will be responsible for distributing tasks among tiers and translating into suitable languages for each tier --- for instance, translating part of a program into Javascript to run in the browser, Java to run on the server, and SQL to run on the database. Links will incorporate ideas proven in other programming languages: support for database programming from Kleisli, for XML programming from Xduce, for web interaction from PLT Scheme, and for distribution from Erlang. It will be developed by a consortium, as were ML and Haskell. Like all of these languages, it will be functional.

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