Toward the end of his presentation Don’t fear the Monad, Brian Beckman makes an interesting observation. He says that early in the history of programming, languages split into two categories: those that start from the machine and add layers of abstraction, and those that start from mathematics and work their way down to the machine.

These two branches are roughly the descendants of Fortran and Lisp respectively. Or more theoretically, these are descendants of the Turing machine and the lambda calculus. By this classification, you could call C# a bottom-up language and Haskell a top-down language.

Programmers tend to write software in the opposite direction of their language’s history. That is, people using bottom-up languages tend to write their software top-down. And people using top-down languages tend to write their software bottom-up.

Programmers using bottom-up languages tend to approach software development analytically, breaking problems into smaller and smaller pieces. Programmers using top-down languages tend to build software synthetically. Lisp programmers in particular are fond of saying they grow the language up toward the problem being solved.

You can write software bottom-up in a bottom-up language or top-down in a top-down language. Some people do. Also, the ideas of bottom-up and top-down are not absolutes. Software development (and language design) is some mixture of both approaches. Still, as a sweeping generalization, I’d say that people tend to develop software top-down in bottom-up languages and bottom-up in top-down languages.

The main idea of Brian Beckman’s video is that algebraic structures like monoids and monads inspire programming models designed make composition easier. This could explain why top-down languages enable or even encourage bottom-up development. It’s not as clear to me why bottom-up languages lead to top-down development.

Related post: Functional in the small, OO in the large