Tuesday, 4 September 2012

Functional makes for an easier Agile

An "agile" approach is concerned with how we approach the management of resources in environments that contain risk factors that cannot be a-priori controlled. Specifically, it is about increasing the tolerance of systems and processes to unanticipated change.

"Functional" development is concerned with how we reason about problems, suggesting a perspective that values a decomposition of the problem into stateless declarative truths over a decomposition of the problem into stateful (albeit small and easy to understand) components (each a small simulacrum of some corner of the problem domain).

Here I am assuming that there is a close (identity?) relationship between a complete analysis of the problem and the solution to that problem - although this may simply be some little remnant of Prolog haunting what is left of my faculties.

It should be possible to behave in an agile manner with both functional and (well designed) OO models, but in my mind, the statelessness of pure functions makes it very much easier to reason about them, and the implications of using them, in unanticipated and rapidly changing situations.

In other words, functional programming is a human --> human communications mechanism, where the extra rigor that the statelessness requirement imposes reduces the number of possibilities that the reader must consider when attempting to modify a model to meet a changed (or novel) requirement.

In summary, "Agile" and "functional" programming are different beasts, but the "functional" approach is very well suited to agile development by virtue of it's enforced "discipline" of statelessness and corresponding reduction in degrees-of-freedom, resulting in reduced mental burden on the maintainer.

We can deduce something from this.

It appears that the more "disciplined" the modeling and programming paradigm, the easier it is to modify and manipulate those models, and to operate in an agile manner, so whilst disciplined programming techniques are not necessarily required for an agile approach to development, the ease with which the agile approach may be taken up benefits greatly from the adoption of highly disciplined programming techniques such as TDD and Functional programming.

If we want to push forwards the state-of-the-art, we should be looking for more ways that we can automatically enforce restrictions upon software models, as well as improve our ability to reason about them.

Hence my interest in TDD, formal methods, assertions and all forms of development automation as a mechanism to make agility easier to achieve.