This survey presents information concerning the use of functional languages (both strict and non-strict) for teaching in higher education. It lists the languages used by over 70 different institutions, the years in which the courses are given, and the recommended textbooks.

This paper provides a formal treatment of isomorphic types for languages equipped with an ML style polymorphic type inference mechanism. The results obtained make less justified the commonplace feeling that (the core of) ML is a subset of second order λ-calculus: we can provide an isomorphism of types that holds in the core ML language, but not in second order λ-calculus. This new isomorphism allows to provide a complete (and decidable) axiomatization of all the types isomorphic in ML style languages, a relevant issue for the type as specifications paradigm in library searches. This work is a very extended version of Di Cosmo (1992): we provide both a thorough theoretical treatment of the topic and describe a practical implementation of a library search system so that the paper can be used as a reference both by those interested in the formal theory of ML style languages, and by those simply concerned with implementation issues. The new isomorphism can also be used to extend the usual ML type-inference algorithm, as suggested by Di Cosmo (1992). Building on that proposal, we introduce a better type-inference algorithm that behaves well in the presence of non-functional primitives like references and exceptions. The algorithm described here has been implemented easily as a variation to the Caml-Light 0.4 system.

List terminators are discussed as a new form of qualifier in list comprehensions for early termination of a list. The semantics of list terminators is expressed in terms of an optimal translation of list comprehensions (cf. Wadler, 1987) because it makes direct use of a continuation list.

In this paper we describe an implementation of an interactive version of the purely functional programming language Lazy ML (LML). The most remarkable fact about the interactive system is that it is written in a pure functional style using LML, yet the efficiency still compares favourably to other conventional interpretative systems.

We describe how the system is designed, and also the exception mechanism that was added to facilitate the handling of errors in the system.

We describe the Edinburgh SML Library and draw lessons from its development. These lessons are of two kinds. The first concerns how to use SML to write a library, and shows some of the design choices that have to be considered. Most of the paper concerns this topic. The second kind of lesson concerns ways in which the language hinders the construction of a library. We suggest some changes to the language as a result of this experience, the most important being the addition of higher-order functors. We also suggest that language designers should consider the needs of libraries early on in the design of a language.

Most programming environments for functional languages offer a single tool used to evaluate programs – either a batch compiler or an interpreter with a read-eval-print loop. This paper presents a programming environment that supports not only evaluation, but also a range of other programming activities including transformation. The environment is designed to encourage working in an incremental and exploratory style, avoiding constraints on the order in which things must be done yet guarenteeing security. What has already been done towards the development of a program automatically persists, as does information about what has yet to be done. For instance, new laws can be introduced as conjectures and used in program transformation, but full details of proof obligations and dependencies are maintained.

The paper outlines the functional language supported by the environment, and uses an extended example to illustrate program construction, execution, tracing, modification and transformation.