Extended ML is a framework for the formal development of programs in the Standard ML programming language from high-level specifications of their required input/output behaviour. It strongly supports the development of modular programs consisting of an interconnected collection of generic and reusable units. The Extended ML framework includes a methodology for formal program development which establishes a number of ways of proceeding from a given specification of a programming task towards a program. Each such step gives rise to one or more proof obligations which must be proved in order to establish the correctness of that step. This paper is intended as a user-oriented summary of the Extended ML language and methodology. Theoretical technicalities are avoided whenever possible, with emphasis placed on the practical aspects of formal program development. An extended example of a complete program development in Extended ML is included.

An overview of past, present and future work on the Extended ML formal program development framework is given, with emphasis on two topics of current active research: the semantics of the Extended ML specification language, and tools to support formal program development.

Functional programming languages have traditionally lacked complete, flexible, and yet referentially transparent I/O mechanisms. Previous proposals for I/O have used either the notion of lazy streams or continuations to model interaction with the external world. We discuss and generalize these models and introduce a third, which we call the systems model, to perform I/O. The expressiveness of the styles are compared by means of an example. We then give a series of surprisingly simple translations between the three models, demonstrating that they are not as different as their programming styles suggest, and implying that the styles could be mixed within a single program. The need to express non-deterministic behavior in a functional language is well recognized. So is the problem of doing so without destroying referential transparency. We survey past approaches to this problem, and suggest a solution in the context of the I/O models described. The I/O system of the purely func...

This thesis presents and justifies a framework for programming real-time signal processing systems. The framework extends the existing "block-diagram" programming model; it has three components: a very high-level textual language, a visual language, and the dataflow process network model of computation. The dataflow process network model, although widely-used, lacks a formal description, and I provide a semantics for it. The formal work leads into a new form of actor. Having established the semantics of dataflow processes, the functional language Haskell is layered above this model, providing powerful features---notably polymorphism, higher-order functions, and algebraic program transformation---absent in block-diagram systems. A visual equivalent notation for Haskell, Visual Haskell, ensures that this power does not exclude the "intuitive" appeal of visual interfaces; with some intelligent layout and suggestive icons, a Visual Haskell program can be made to look very like a block dia...

This paper presents the Visual Haskell language. Visual Haskell is intended as i) a means of visualising Haskell programs, and ii) as a complementary programming notation to standard Haskell. The syntax of Visual Haskell is specified by first giving a translation from Haskell into an intermediate, textual form; the visual syntax is then specified as a direct translation from the intermediate form into visual representations. Visual Haskell is kept as close to Haskell as possible, in the hope that it could be used in a "two-view" programming system. Several examples of function definitions illustrate how Visual Haskell looks and is used. Visual Haskell is incomplete, lacking syntax for modules, type declarations, type classes and instances, arrays, and user-defined operators. These are seen as temporary omissions rather than insurmountable drawbacks. 1 Introduction This paper presents Visual Haskell, my attempt to develop a visual equivalent for the Haskell functional language [4]. Vis...

This paper describes a computer architecture for execution of lazy functional languages. The architecture is based on graph reduction of the -calculus, but is extended to handle real programs. It is not another abstract machine, but instead a proposal for how actual hardware could be designed. The machine uses very large memory words. This makes it possible for a single instruction to do a lot (akin to VLIW and superscalar machines), and also to construct and scrutinize large objects with few memory operations. Since construction of suspensions is a very common operation during graph reduction this is beneficial. The machine is built around a stack and a multiplexor, not around an arithmetic unit as most stock processors. The reason for this is that this machine is not aimed at number crunching, but at manipulating data. As with modern RISC processors the interaction between the compiler and the processor is crucial; the "hardware" has several shortcomings that the compiler has to know...

We describe the design and use of monadic I/O in Haskell 1.3, the latest revision of the lazy functional programming language Haskell. Haskell 1.3 standardises the monadic I/O mechanisms now available in many Haskell systems. The new facilities allow fairly sophisticated text-based application programs to be written portably in Haskell. The standard provides implementors with a flexible framework for extending Haskell to incorporate new language features. Apart from the use of monads, the main advances over the previous standard are: character I/O based on handles (analogous to ANSI C file pointers), an error handling mechanism, terminal interrupt handling and a POSIX interface. Apart from a tutorial description of the new facilities we include a worked example: a derived monad for combinator parsing. 1 Introduction Haskell 1.3 improves on previous versions of Haskell [12] by adopting an I/O mechanism based on monads [19]. This paper explains the structure of this monadic I/O mechanis...

I declare that this thesis is my own account of my research and contains as its main content work which has not previously been submitted for a degree at any tertiary education institution. Joel Kelso ii The purported advantages of Visual Programming, as applied to general purpose programming languages, have remained largely unfulfilled. The essence of this thesis is that functional programming languages have at least one natural visual representation, and that a useful programming environment can be based upon this representation. This thesis describes the implementation of a Visual Functional Programming Environment (VFPE). The programming environment has several significant features. • The environment includes a program editor that is inherently

DataTypes : : : : : : : : : : : : : : : : : : : : : : : : : 40 4.2 PolymorphicDataTypes : : : : : : : : : : : : : : : : : : : : : : : 40 vi 4.3 Existential DataTypes : : : : : : : : : : : : : : : : : : : : : : : : 41 4.4 DynamicTypes : : : : : : : : : : : : : : : : : : : : : : : : : : : : 43 4.5 Dynamic Semantics : : : : : : : : : : : : : : : : : : : : : : : : : : 45 5 A Tiny Programming Language 48 5.1 Tiny Layout Conventions : : : : : : : : : : : : : : : : : : : : : : 48 5.2 Existential Type Variables : : : : : : : : : : : : : : : : : : : : : : 50 5.3 Type Signatures withHoles : : : : : : : : : : : : : : : : : : : : : 50 5.4 PolymorphicAbstractions : : : : : : : : : : : : : : : : : : : : : : 51 5.5 Top-Level Function Signatures : : : : : : : : : : : : : : : : : : : : 53 5.6 AlgebraicDataTypes : : : : : : : : : : : : : : : : : : : : : : : : 54 5.7 Restricted Type Synonyms and Newtype : : : : : : : : : : : : : : 55 5.8 Summary of Type System : : : : : : : : : : : : : : : : : : : : : : 56 5.9 DynamicTypes : : : : : : : : : : : : : : : : : : : : : : : : : : : : 57 6 Systems Programming with Dynamic Types 59 6.1 Error Handling : : : : : : : : : : : : : : : : : : : : : : : : : : : : 59 6.2 Inter-Process Communication : : : : : : : : : : : : : : : : : : : : 62 6.3 A Simple Address Server : : : : : : : : : : : : : : : : : : : : : : : 64 6.4 A Simple File Server : : : : : : : : : : : : : : : : : : : : : : : : : 66 6.5 A Capability System : : : : : : : : : : : : : : : : : : : : : : : : : 69 6.6 Distributed Inter-Process Communication : : : : : : : : : : : : : 75 6.7 A Compiler Interface : : : : : : : : : : : : : : : : : : : : : : : : : 78 6.8 AFunctional Compiler Interface : : : : : : : : : : : : : : : : : : 81 7 Dynamic Overloading 83 7.1 Dynamically Resolved Overloading : : ...

This thesis presents and justi es a framework for programming real-time signal process-ing systems. The framework extends the existing \block-diagram " programming model� it has three components: a very high-level textual language, a visual language, and the data ow process network model of computation. The data ow process network model, although widely-used, lacks a formal description, and I provide a semantics for it. The formal work leads into a new form of actor. Having established the semantics of data ow processes, the functional language Haskell is layered above this model, providing powerful features|notably polymorphism, higher-order func-tions, and algebraic program transformation|absent in block-diagram systems. A visual equivalent notation for Haskell, Visual Haskell, ensures that this power does not exclude the \intuitive " appeal of visual interfaces � with some intelligent layout and suggestive icons, a Visual Haskell program can be made to look very like ablock diagram program. Finally, the functional language is used to further extend data ow process networks, by simulating timed and dynamically-varying networks.