I was recently reading about Exceptions in Java and discovered they aren't resumable. You can't pick-up from where an exception was thrown. I began wondering how this might be possible in Java, but it would require a change to Java's syntax--or the language. Why?
Java doesn't support code blocks as objects. New functionality can't be introduced to blocks of code without changing the language itself. try/catch/finally is implemented as part of the language and not as a feature of an object.
Also, because Java as statically typed it would be nearly impossible to resume with a new value anyway since the "throw" command would have to be able to return a value--but since throw is a command it doesn't return values--and even if it did it would have to return the amorphous "object" which would then require down casting to be made useful. Even then it may be impossible to resume processing with an alternative primitive value.
So Java programs have to run while{}s outside their try{}catch{}s to correct something--which makes the granularity of what can be retried fairly large. Meaning, if there are side effects inside try{} they will either need to be reexecutable without additional (bad) effects or whatever they did will require undoing (or inoculation) inside the catch{}.
In Smalltalk, however, interesting features can be added to blocks and exceptions because they're objects, and object's behavior can be extended without subclassing and is possible in the first place because they aren't "final" nor closed in the base library.
Smalltalk is even neater now than it was a few weeks ago.
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