This paper reports research to define a set of interaction parameters that collaborative writers will find useful. Our approach is to provide parameters of interaction and to locate the decision of how to set the parameters with the users. What is new in this paper is the progress we have made outlining task management parameters, notification, scenarios of use, as well as some implementation architectures.

An important activity in collaborative writing is communicating about changes to texts,, This paper reports on a software system, ji'exible cliff, that finds and reports differences ("cliffs") between versions of texts.The system is flexible, allowing users to control several aspects of its operation including what changes are reported and how they are shown when they are reported.We argue that such flexibility is necessary to support users' different social and cognitive needs.

This paper reports on a project to develop a “work in preparation” editor, or PREP editor, to study co-authoring and commenting relationships. As part of the project, we have identified three issues in designing computer support for co-authoring and commenting: (1) support for social interaction among co-authors and commenters; (2) support for cognitive aspects of co-authoring and external commenting; and (3) support for practicality in both types of interaction. For each of these issues, the paper describes the approach the PREP editor takes to address them.

Experience using and implementing the language Poplar is described. The major conclusions are: Applicative programming can be made more natural through the use of built-in iterative operators and post-fix notation. Clever evaluation strategies, such as lazy evaluation, can make applicative programming more computationally efficient. Pattern matching can be performed in an applicative framework. Many problems remain.

An algorithm is presented which finds all occurrences of one given string within another, in running time proportional to the sum of the lengths of the strings. The constant of proportionality is low enough to make this algorithm of practical use, and the procedure can also be extended to deal with some more general pattern-matching problems. A theoretical application of the algorithm shows that the set of concatenations of even palindromes, i.e., the language $\{\alpha \alpha ^R\}^*$, can be recognized in linear time. Other algorithms which run even faster on the average are also considered.

A different way to execute pure LISP programs is presented. It delays the evaluation of parameters and list structures without ever having to perform more evaluation steps than the usual method. Although the central idea can be found in earlier work this paper is of interest since it treats a rather well-known language and works out an algorithm which avoids full substitution. A partial correctness proof using Scott-Strachey semantics is sketched in a later section.

The title is not a statement of fact, of course, but an opinion about how language designers should think about types. There has been a natural tendency to look to mathematics for a consistent, precise notion of what types are. The point of view there is extensional: a type is a subset of the universe of values. While this approach may have served its purpose quite adequately in mathematics, defining programming language types in this way ignores some vital ideas. Some interesting developments following the extensional approach are the ALGOL-68 type system [vW], Scott's theory [S], and Reynolds' system [R]. While each of these lend valuable insight to programming languages, I feel they miss an important aspect of types.Rather than worry about what types are I shall focus on the role of type checking. Type checking seems to serve two distinct purposes: authentication and secrecy. Both are useful when a programmer undertakes to implement a class of abstract objects to be used by many other programmers. He usually proceeds by choosing a representation for the objects in terms of other objects and then writes the required operations to manipulate them.

Scheme translation is used to compare the abilities of languages obtained by augmenting recursion schemes with lists, markers, and functional values. It is shown that the first two additions make orthogonal contributions to the language's power. Theorems 4 and 5 appear to be new results.