The Common Gateway Interface (CGI) for generating dynamic documents on web servers imposes much accidental complexity on the programmer. The Haskell/CGI library documented in this paper hides all this unpleasantness by using the common sense ‘design pattern’ of separating model and presentation. Low-level query string requests are represented by association lists, and primitive HTTP responses are easily constructed using a set of HTML generating combinators. The CGI programmer only needs to write a worker function that maps an abstract request into an abstract response. A (higher-order) wrapper function then transmutes the worker into a real low-level CGI script that deals with the exact format of concrete requests and responses as required by the CGI standard.

Kleisli is a modern data integration system that has made a significant impact on bioinformatics data integration. This paper contains a brief introduction to the Kleisli system and an example to illustrate its uses in the bioinformatics arena. The primary query language provided by Kleisli is called CPL, which is a functional query language whose surface syntax is based on the comprehension syntax. Kleisli is itself implemented using the functional language SML. So this paper also describes the influence of functional programming research that benefits the Kleisli system, especially the less obvious ones at the implementation level.

Availability. Kleisli has been commercialized under the name “KRIS”. It is available from Kris Technology Inc., 713 Santa Cruz Ave, #2, Menlo Park, CA 94025, USA. Direct email to info@kris-inc.com and web browser to http://www.kris-inc.com.

The understanding of polymorphic typechecking and type errors is poorly supported by contemporary functional language implementations. Here, a novel visualisation of functions and their types is presented based on the generation of function specific icons with graphical type representations which change dynamically as functions are applied. This visualisation has been implemented for a Standard ML subset within a graphical environment in which function combinations are constrained by type matching.

We present a short proof of a folklore result: the Girard translation from the simply typed lambda calculus to the linear lambda calculus is fully complete. The proof makes use of a notion of logical predicates for intuitionistic linear logic. While the main result is of independent interest, this paper can be read as a tutorial on this proof technique for reasoning about relations between type theories.

We present our experience in implementing a group communication toolkit in Objective Caml, a dialect of the ML family of programming languages. We compare the toolkit both quantitatively and qualitatively to a predecessor toolkit which was implemented in C. Our experience shows that using the high-level abstraction features of ML gives substantial advantages. Some of these features, such as automatic memory management and message marshalling, allowed us to concentrate on those pieces of the implementation which required careful attention in order to achieve good performance. We conclude with a set of suggested changes to ML implementations.

It is well known that there is an isomorphism between natural deduction derivations and typed lambda terms. Moreover, normalising these terms corresponds to eliminating cuts in the equivalent sequent calculus derivations. Several papers have been written on this topic. The correspondence between sequent calculus derivations and natural deduction derivations is, however, not a one-one map, which causes some syntactic technicalities. The correspondence is best explained by two extensionally equivalent type assignment systems for untyped lambda terms, one corresponding to natural deduction (λN) and the other to sequent calculus (λL). These two systems constitute different grammars for generating the same (type assignment relation for untyped) lambda terms. The second grammar is ambiguous, but the first one is not. This fact explains the many-one correspondence mentioned above. Moreover, the second type assignment system has a ‘cut-free’ fragment (λLcf). This fragment generates exactly the typeable lambda terms in normal form. The cut elimination theorem becomes a simple consequence of the fact that typed lambda terms possess a normal form.

Logical frameworks and meta-languages are intended as a common substrate for representing and implementing a wide variety of logics and formal systems. Their definition and implementation have been the focus of considerable work over the last decade. At the heart of this work is a quest for generality: A logical framework provides a basis for capturing uniformities across deductive systems and support for implementing particular systems. Similarly a meta-language supports reasoning about and using languages.

Logical frameworks have been based on a variety of different languages including higher-order logics, type theories with dependent types, linear logic, and modal logic. Techniques of representation of logics include higher-order abstract syntax, inductive definitions or some form of equational or rewriting logic in which substitution is explicitly encoded.

Examples of systems that implement logical frameworks include Alf, Coq, NuPrl, HOL, Isabelle, Maude, lambda-Prolog and Twelf. An active area of research in such systems is the study of automated reasoning techniques. Current work includes the development of various automated procedures as well as the investigation of rewriting tools that use reflection or make use of links with systems that already have sophisticated rewriting systems. Program extraction and optimization are additional topics of ongoing work.