We've come to be pretty leery of exceptions at Jane Street, and we've had some experience trying to control their use  Some quick observations on the current proposal:
  1. Banning exceptions outright seems too strict.  Our tendency has been to have two versions of the function, e.g., Map.find and Map.find_exn.  (Our previous approach would have been to use Map.find_opt for the one that returns and option and Map.find for the exception-throwing one, but we're slowly migrating to the first proposal.)  The goal is to make the user aware that an exception is reasonably likely, rather than ban exceptions.
  2. We've played around with monadic error systems that combine errors into a big polymorphic variant.  The key practical problem we hit were obscenely complicated error messages.  Still, in some cases, monads are very nice.
  3. Having a variant type other than option so you can specify various different errors (ours is Ok of 'a | Error of 'b) is a good idea.  And I think it's common enough that you should define it in your core library as an ordinary variant and make it available everywhere.
y



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