ex

warning: ex is experimental at this point

Yet another exception library with support for ex-info.

So we have qbits.ex/try+, which supports vanilla catch/finally clauses.

If you specify a catch-data clause with a keyword as first argument things get interesting.

I thought leveraging a clojure hierarchy could make sense in that context too (I like these lately), other than that it's largely inspired by catch-data, the implementation is slightly different, we dont catch Throwable, we instead generate a catch clause on clj.exinfo and generate a cond that tries to match ex-data with the :type key, which arguably is closer to what you (or I?) would write by hand in that case.

We start with the assumption that the ex-data map contains a :type key, as we think it's generally a good practice to do so. That key should contain a keyword (namespaced or not) and we should be able to match the right clause from it, or just throw the ex-info if there's no match.

(require '[qbits.ex :as ex])

(ex/try+

  (throw (ex-info "Argh" {:type ::bar :foo "a foo"}))

  (catch-data ::foo data
    (prn :got-ex-data data))

  (catch-data ::bar {:as data :keys [foo]}
    ;; in that case it would hit this one
    (prn :got-ex-data-again foo))

  (catch ExceptionInfo e
   ;; this would match an ex-info that didn't get a hit with catch-ex-info)

  (catch Exception e (prn :boring))

  (finally (prn :boring-too)))

Then we have an internal hierarchy, so you can do things like that:

;; so bar is a foo

(ex/derive ::bar ::foo)

(ex/try+
  (throw (ex-info "I am a bar" {:type ::bar})
  (catch-data ::foo d
    (prn "got a foo with data" d)
    (prn "Original exception instance is " (-> d meta ::ex/exception))))

You can also get the full exception instance via the metadata on the ex-data we extract, it's under the :qbits.ex/exception key.

License

Copyright © 2018 Max Penet

Distributed under the Eclipse Public License, the same as Clojure.