[lmm]

As an industrial engineer, monads are the best solution I've ever found to the cross-cutting concern problem. I need to be able to put custom cross-cutting concerns on my functions - things like must-happen-in-database-transaction, record-in-audit-log, must-have-this-authorisation-level, record-these-statistics. If your language doesn't have monads, you end up using reflective proxies, metaclasses, decorators, bytecode modification, macros, or something equally incomprehensible.

I'd love to have a better alternative. Maybe one day one of these "effect systems" will actually get a production-quality implementation. But until then monads are the least-bad option out of everything that I've seen tried.

[johnday]

Absolutely. It's worth noting that every single effect system implementation that currently exists also leverages monads at the user level, even if they're doing exciting type-theoretic things underneath.