Thanks for your question. I should have been more careful. I meant Agda used as a prover, not Agda used as a 'conventional' programming language (Indeed in years of usage, I've never executed an Agda program, I've only ever used the type checker). In other words, Agda, the proof calculus for Martin-Loef type theory.

That said, I was talking about effects in general, including non-termination, exceptions, concurrency ...