The purpose of my remark is how they look like in terms of usage for the humble programmer.<p>They being similar how having a limited data structure (non extensible) with a set of functions that operate on it. Depending on the FP language ADTs can also partially hide their implementation like the Abstract Data Types in modular languages.<p>But I can also happily discuss the math theory and the denotational semantics about them across languages, but I don&#x27;t think it will help for many readers.