> Defer is basically finally without block structure, triggered instead by the popping of the surrounding procedural call context. So instead of a block, you have to create a new function instead to unwind...how is the extra complexity of avoiding simple block structure worth it?

How is function structure any more complex than block structure?(I mean, visually, sure, there are potentially a few extra sigils, but structurally how is a block different than a nullary function?)

> And what is the equivalent of catch if we have an equivalent of finally?

Recover within a deferred function provides the ability to do the functionality of catch -- I wouldn't call it a one-for-one equivalent (the combination of features is equivalent, but there isn't a one-for-one correspondence between the individual features except between panic and raise/throw.)