> It's also possible that you never have a real need to do these things.
What I don't have a real need for is the ability to destroy the internal invariants of other modules. :-p
> True, which is why I'm pretty confident that 15 years of Smalltalk development on many large code bases without running into a heterogeneous collection debugging conundrum is possibly a valid data point.
Who says homogeneous collections are the only use case for parametricity? Parametricity is useful whenever you need to make sure that unrelated parts of your program don't accidentally rely on (or, even worse, alter) each other's implementation details. “Modularity”, as they call it elsewhere. Of course, Smalltalk has none of this.
> My impression is that the damage caused by "hubris coding," or the gratuitous worship of "cleverness," far outweighs that caused by insufficient type information by 2 or 3 orders of magnitude.
I don't separate concerns to be “clever”. Au contraire! I separate concerns to deal with my own brain's limited ability to simultaneously process multiple pieces of information. (And I'll be perfectly honest: I also separate concerns because it's beautiful.)
“Hubris” is a term I would reserve for those who write large programs whose constituent parts don't have fixed structure, yet claim they understand what's going on in the code. (Or perhaps they claim “the tests do the understanding”?)
