[grumpyprole]

Java has always had checked exceptions, a weak form of type-checked effect. They were controversial because developers didn't like being forced to handle them, but I always thought they were a great idea. Algebraic effect handlers just generalise the idea of an exception, by providing a continuation that can be called to resume execution.

[infogulch]

The problem with Java exceptions is that they are used to paper over the lack of multiple return values for totally mundane situations where there are genuinely multiple possible outcomes. "tried to open file that doesn't exist", "tried to open a socket to a domain that couldn't be resolved", "user doesn't have permission to perform that action", etc, are normal failures not exceptional. But all of these totally normal outcomes are mediated by the same language feature that also deals with indexing past the end of an array or dereferencing null, both of which are clearly program bugs. That's why checked exceptions were controversial: they were a noisy workaround for proper language tool to manage multiple outcomes. Go takes a small step towards fixing this by making packing and unpacking tuples easy and normalizing returning an error as the last tuple value; rust and other languages with discriminated unions and an integrated match actually solves this.

I guess if it helps you understand typed effects if you describe it as "java checked exceptions with an option to resume" then I'm glad that works for you, but for me, Java exceptions have so much other baggage surrounding their design that I would prefer describing it from the other direction: "typed effects would enable you to implement a host of cross-stack features, including a checked exception system like Java's".

[grumpyprole]

I am not advocating Java the language and it's shortcomings are really the topic of another thread. I am also not seeking to understand algebraic effects starting from Java, I've read the original Eff paper and would encourage others to do so. I raised them only as an example of a form of type checked effect that is already in widespread use.