Jonas's work-in-progress utility library
- bluebell.utils.dsl A tool to build DSLs explained here.
- bluebell.utils.render-test A DSL to render text with indentation.
- bluebell.utils.ebmd Example-based multiple dispatch explained here.
An error context is an, ehmm, mutable object to help with the control flow in case of error handling. It is normally constructed using the context function context. Internally, it tracks whether errors occur and, if that is the case, prevent computations from taking place.
It is practical for factoring out error-handling business and does not need macros to hide what is going on:
;; We can factor out the details about errors...
(defn stacked-ex-context []
(-> (context)
(maperr-when (partial instance? Exception)
(constantly :exception))
(maperr-when (partial instance? ArithmeticException)
(constantly :arithmetic-exception))))
;; ..and then reuse it.
(deftest maperr-when-test
(is (= 7 (with-export (stacked-ex-context)
7)))
(is (= :exception (with-export (stacked-ex-context)
(throw (ex-info "Kattskit" {})))))
(is (= :arithmetic-exception (with-export (stacked-ex-context)
(/ 8 0)))))See the unittests bluebell.utils.error-context-test for examples.
Why error context over exceptions?:
* Makes error handling more explicit by requiring the use of a context to control execution based on whether an error occurred, without cluttering the code with if-let forms.
* Isolate error handling to parts of the code and then wrap it up in the end, with a call to export.
* Handle situations where it would be a bit brutal to throw an exception, e.g. situations such as spec/conform returning spec/invalid.
* Factor out the details about error handling in functions.
* Decouple error values and control flow.
* Usecases: Trying to compute mean of an empty array
Copyright © 2018 Jonas Östlund
Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.