arXiv subjects

John Whitington

Publications and source records attributed to John Whitington.

4 recordsLinked to original sources

arXiv2024

Visualizing the Evaluation of Functional Programs for Debugging

In this position paper, we present a prototype of a visualizer for functional programs. Such programs, whose evaluation model is the reduction of an expression to a value through repeated application of rewriting rules, and which tend to make little or no use of mutable state, are amenable to visualization in the same fashion as simple mathematical expressions, with which every schoolchild is familiar. We show how such visualizations may be produced for the strict functional language OCaml, by direct interpretation of the abstract syntax tree and appropriate pretty-printing. We describe (and begin to address) the challenges of presenting such program traces in limited space and of identifying their essential elements, so that our methods will one day be practical for more than toy programs. We consider the problems posed by the parts of modern functional programming which are not purely functional such as mutable state, input/output and exceptions. We describe initial work on the use of such visualizations to address the problem of program debugging, which is our ultimate aim.

cs.PL↗

arXiv2024

Debugging Functional Programs by Interpretation

Motivated by experience in programming and in the teaching of programming, we make another assault on the longstanding problem of debugging. Having explored why debuggers are not used as widely as one might expect, especially in functional programming environments, we define the characteristics of a debugger which make it usable and thus likely to be widely used. We present work on a new debugger for the functional programming language OCaml which operates by direct interpretation of the program source, allowing the printing out of individual steps of the program's evaluation, and discuss its technical implementation and practical use. It has two parts: a stand-alone debugger which can run OCaml programs by interpretation and so allow their behaviour to be inspected; and an OCaml syntax extension, which allows the part of a program under scrutiny to be interpreted in the same fashion as the stand-alone debugger whilst the rest of the program runs natively. We show how this latter mechanism can create a source-level debugging system that has the characteristics of a usable debugger and so may eventually be expected to be suitable for widespread adoption.

cs.PL↗

arXiv2024

Two Dimensional Hidden Surface Removal with Frame-to-frame Coherence

We describe a hidden surface removal algorithm for two-dimensional layered scenes built from arbitrary primitives, particularly suited to interaction and animation in rich scenes (for example, in illustration). The method makes use of a set-based raster representation to implement a front-to-back rendering model which analyses and dramatically reduces the amount of rasterization and composition required to render a scene. The method is extended to add frame-to-frame coherence analysis and caching for interactive or animated scenes. A powerful system of primitive-combiners called filters is described, which preserves the efficiencies of the algorithm in highly complicated scenes. The set representation is extended to solve the problem of correlated mattes, leading to an efficient solution for high quality antialiasing. A prototype implementation has been prepared.

cs.GR↗

arXiv2019

Direct Interpretation of Functional Programs for Debugging

We make another assault on the longstanding problem of debugging. After exploring why debuggers are not used as widely as one might expect, especially in functional programming environments, we define the characteristics of a debugger which make it usable and thus widely used. We present initial work towards a new debugger for OCaml which operates by direct interpretation of the program source, allowing the printing out of individual steps of the program's evaluation. We present OCamli, a standalone interpreter, and propose a mechanism by which the interpreter could be integrated into compiled executables, allowing part of a program to be interpreted in the same fashion as OCamli whilst the rest of the program runs natively. We show how such a mechanism might create a source-level debugging system that has the characteristics of a usable debugger (such as being independent of its environment) and so may eventually be expected to be suitable for widespread adoption.

cs.PL↗