Unfortunately, it conceals it behind some examples that - while they do a good job of illustrating the generality of its applicability - don’t show as well how to use this in your own code.
Most developers are not writing their own head method on the list primitive - they are trying to build a type that encapsulates a meaningful entity in their own domain. And, let’s be honest, most developers are also not using Haskell.
As a result I have not found this article a good one to share with junior developers to help them understand how to design types to capture the notion of validity, and to replace validation with narrowing type conversions (which amount to ‘parsing’ when the original type is something very loose like a string, a JSON blob, or a dictionary).
Even though absolutely those practices follow from what is described here.
Does anyone know of a good resource that better anchors these concepts in practical examples?