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src/cognitect for ClojureScript Oct 11, 2018
README.md category table Jul 24, 2017

README.md

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 retry fix song
:unavailable yes make sure callee healthy Out of Touch
:interrupted yes stop interrupting It Doesn't Matter Anymore
: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 no fix callee bug Falling
:busy yes backoff and retry Wait For Me

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

Copyright (c) Cognitect, Inc. All rights reserved.

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.