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Row Polymorphic Programming
Sometimes, especially when dealing with business logic, we have to deal with data that comes in from the real world, or elsewhere, naturally very messily typed, leading to nasty type signatures and messes of macros or code generation to build data structures from a schema. Row polymorphism can help us by abstracting over the fields contained in a record type in the type signature, letting us define records based on data, concatenate records together, and define functions that are generic across any record containing the required fields, all without macros.
Two columns in two different tables having the same names and types doesn't always mean that they are semantically equivalent, but its often a pretty good bet, especially when they are coming from related sources. Other tasks like frontend work, business logic, and video games quite frequently deal with extremely messy data that has only loosely defined shape and doesn't want to fit neatly into a type hierarchy, leaving you with a lot to gain from row polymorphism. In this specific context, we do have to explicitly provide the schema to the area function to disambiguate, but this can be avoided with more careful design and should be considered more of an artifact of the limited implementation in this article then an intrinsic ergonomics concern with this approach to programming in Idris.
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