Awesome

cognitect.anomalies

Rationale

Anomalies capture errors as information that is simple, actionable, generic, and extensible.

Simple: Anomalies contain only information about the error, not e.g. flow control or causality.
Actionable: the ::anom/category aims to be a top-level partitioning of all kinds of errors, allowing many programs that need to branch during error-handling to branch only on this keyword.
Generic: Anomalies are represented as ordinary maps, and can be created and consumed without any special API.
Extensible: As maps are open, applications can add their own context via namespaced keywords. That said, try to do as much as possible by dispatching only via ::anom/category.

Anomalies overlap in purpose with e.g. Java exceptions and HTTP responses. The differences are instructive:

Java exceptions are not simple, as they combine error information with a flow control mechanism. This is a problem in e.g. async applications and transductions. Both of these contexts need to talk about errors, but do not want to utilize exceptions' flow control by stack unwinding.

HTTP responses provide useful partitioning via status codes. But since status codes appear inside a server response they cannot possibly cover e.g. failure to get a response at all.

The Categories

The category column contains the name of an anomaly category within the cognitect.anomalies namespace.

The retry column is "yes" if a replay of the same activity might reasonably lead to a different outcome. When a program encounters a retryable anomaly, it may be reasonable to back off and try again.

The "fix" column provides an example of how a programmer or operator might fix problems in this category.

The "song" column contains a Hall and Oates song. The idea that Hall and Oates are software gurus is controversial in some circles, so you can treat this as flavortext.

category	retryable?	fix	song
:unavailable	yes	make sure callee healthy	Out of Touch
:interrupted	maybe	stop interrupting	It Doesn't Matter Anymore
:busy	yes	backoff and retry	Wait For Me
:incorrect	no	fix caller bug	You'll Never Learn
:forbidden	no	fix caller creds	I Can't Go For That
:unsupported	no	fix caller verb	Your Imagination
:not-found	no	fix caller noun	She's Gone
:conflict	no	coordinate with callee	Give It Up
:fault	maybe	fix callee bug	Falling

Using cognitect.anomalies

Leiningen dependency information:

[com.cognitect/anomalies "0.1.12"]

Maven dependency information:

<dependency>
  <groupId>com.cognitect</groupId>
  <artifactId>anomalies</artifactId>
  <version>0.1.12</version>
</dependency>

Developer Information

Please submit feedback via GitHub issues.

Please do not submit pull requests or patches.

Copyright and License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

 http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS-IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.