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/categoryaims 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.