Partway through, I recognized the function calling syntax as similar to Nix which I just started learning.

Turns out the implementation of the article is in Haskell, another declarative language.

At work. we use Power Query with it's M language - a declarative language with lazy evaluation.

Is there something about declarative languages that makes them especially suitable for data work?

I mean — the ideal of an SQL query is you say what you want, and it’s up to the engine to determine how to give it to you — that is, being declarative.

Part of it is there’s so many different ways to represent data, and even more ways to compute a given quantity — but the quantity itself often has a clear definition (sum this column from all rows where this holds, say)