Logic Programming for the Real World

1 The objective Logic programming languages have been around for more than twenty years. Despite their theoretical advantages over conventional programming languages, they have not had signiicant impact on the computer industry. Most of the 500 applications on the Prolog 1000 list 1 are small by industrial standards (fewer than ten exceed 100,000 lines of code), and very few have a user base exceeding a hundred people. We believe that changing this situation and establishing logic programming as a major paradigm in the non-academic world is an appropriate objective for a successor to Prolog. Convincing programmers to switch to a new language from the languages they are currently using requires the new language to meet two criteria. First, the new language must be demonstrably superior to the user's current language in at least one aspect, and this superiority must be realizable as an economic advantage. Second, the new language must not lack any of the qualities that the programmer values in his or her current language. To meet the rst criterion, a new logic programming language need only realize the advantages that have been promised by logic programming advocates since the inception of the eld. These advantages include the following. Logic programming languages are very expressive, high level languages that allow programmers to concentrate on what must be done, rather than how it should be done. By automating some of their more mundane tasks, logic programming allows programmers to spend their time on more productive endeavors. Automatic memory management, automatic management of searches, and transparent interfaces to relational and deductive databases are three examples. (The last two are unique to logic programming; they are not shared by functional languages.) Logic programming languages have much more useful formal semantics. This makes the automatic analysis and transformation of logic programs much simpler and therefore much more eeective than the analysis and transformation of imperative programs. In theory, this should allow programmers to worry less about eeciency, which again makes them more productive. The semantics of logic programming languages need not prescribe an order of evaluation, which makes it much easier for a compiler to emit parallel code. By comparison, the automatic parallelization of code written in an imperative language requires extensive non-local analysis of the program, and for many programs acceptable results require signiicant user intervention 2]. Logic programming languages have the potential to make debugging much easier, since one can implement …