Title:EEP Purpose and Guidelines
Last-Modified:2007-01-31 17:14:17 +0100 (Wed, 31 Jan 2007)
Author:Per Gustafsson <pergu at>


What is a EEP?

EEP stands for Erlang Enhancement Proposal. It is a concept borrowed from the Python language [1] to facilitate community involvement in developing Erlang. This document is heavily based on PEP 1 [2]. An EEP is a design document providing information to the Erlang community, or describing a new feature for Erlang or its processes or environment. The EEP should provide a concise technical specification of the feature and a rationale for the feature.

We intend EEPs to be the primary mechanisms for proposing new features, for collecting community input on an issue, and for documenting the design decisions that have gone into Erlang. The EEP author is responsible for building consensus within the community and documenting dissenting opinions.

Because the EEPs are maintained as text files in a versioned repository, their revision history is the historical record of the feature proposal [3].

EEP Types

There are three kinds of EEP:

  1. A Standards Track EEP describes a new feature or implementation for Erlang.
  2. An Informational EEP describes a Erlang design issue, or provides general guidelines or information to the Erlang community, but does not propose a new feature. Informational EEPs do not necessarily represent a Erlang community consensus or recommendation, so users and implementors are free to ignore Informational EEPs or follow their advice.
  3. A Process EEP describes a process surrounding Erlang, or proposes a change to (or an event in) a process. Process EEPs are like Standards Track EEPs but apply to areas other than the Erlang language itself. They may propose an implementation, but not to Erlang's codebase; they often require community consensus; unlike Informational EEPs, they are more than recommendations, and users are typically not free to ignore them. Examples include release schedules, procedures, guidelines, changes to the decision-making process, and changes to the tools or environment used in Erlang development.

EEP Work Flow

The EEP editors assign EEP numbers and change their status. The current EEP editors are XX and YY. Please send all EEP-related email to <>.

The EEP process begins with a new idea for Erlang. It is highly recommended that a single EEP contain a single key proposal or new idea. The more focused the EEP, the more successful it tends to be. The EEP editor reserves the right to reject EEP proposals if they appear too unfocused or too broad. If in doubt, split your EEP into several well-focused ones.

Each EEP must have a champion -- someone who writes the EEP using the style and format described below, shepherds the discussions in the appropriate forums, and attempts to build community consensus around the idea. The EEP champion (a.k.a. Author) should first attempt to ascertain whether the idea is EEP-able. Posting to the mailing list is recommended. Small enhancements or patches often don't need a EEP and can be injected into the Erlang development work flow by sending a patch to

The EEP champion then emails the EEP editor <> with a proposed title and a rough, but fleshed out, draft of the EEP. This draft must be written in EEP style as described below.

If the EEP editor approves, he will assign the EEP a number, label it as Standards Track, Informational, or Process, give it status "Draft", and create and check-in the initial draft of the EEP. The EEP editor will not unreasonably deny a EEP. Reasons for denying EEP status include duplication of effort, being technically unsound, not providing proper motivation or addressing backwards compatibility, or not in keeping with the Erlang philosophy.

If a pre-EEP is rejected, the author may elect to take the pre-EEP to the mailing list to help flesh it out, gain feedback and consensus from the community at large, and improve the EEP for re-submission.

The author of the EEP is then responsible for posting the EEP to the community forums, and marshaling community support for it. As updates are necessary, the EEP author can check in new versions if they have SVN commit permissions, or can email new EEP versions to the EEP editor for committing.

Standards Track EEPs consist of two parts, a design document and a reference implementation. The EEP should be reviewed and accepted before a reference implementation is begun, unless a reference implementation will aid people in studying the EEP. Standards Track EEPs must include an implementation -- in the form of code, a patch, or a URL to same -- before it can be considered Final.

EEP authors are responsible for collecting community feedback on a EEP before submitting it for review. A EEP that has not been discussed on the erlang mailing list will not be accepted. However, wherever possible, long open-ended discussions on public mailing lists should be avoided. Strategies to keep the discussions efficient include: setting up a separate SIG mailing list for the topic, having the EEP author accept private comments in the early design phases, setting up a wiki page, etc. EEP authors should use their discretion here.

Once the authors have completed a EEP, they must inform the EEP editor that it is ready for review. EEPs are reviewed by the Erlang/OTP team and their chosen consultants, who may accept or reject a EEP or send it back to the author(s) for revision. For a EEP that is pre-determined to be acceptable (e.g., it is an obvious win as-is and/or its implementation has already been checked in) the Erlang/OTP team may also initiate a EEP review, first notifying the EEP author(s) and giving them a chance to make revisions.

For a EEP to be accepted it must meet certain minimum criteria. It must be a clear and complete description of the proposed enhancement. The enhancement must represent a net improvement. The proposed implementation, if applicable, must be solid and must not complicate the interpreter unduly. Finally, a proposed enhancement must be compatible with the Erlang philosophy in order to be accepted.

Once a EEP has been accepted, the reference implementation must be completed. When the reference implementation is complete and accepted, the status will be changed to "Final".

A EEP can also be assigned status "Deferred". The EEP author or editor can assign the EEP this status when no progress is being made on the EEP. Once a EEP is deferred, the EEP editor can re-assign it to draft status.

A EEP can also be "Rejected". Perhaps after all is said and done it was not a good idea. It is still important to have a record of this fact.

EEPs can also be replaced by a different EEP, rendering the original obsolete. This is intended for Informational EEPs, where version 2 of an API can replace version 1.

EEP work flow is as follows:


Some Informational and Process EEPs may also have a status of "Active" if they are never meant to be completed. E.g. EEP 1 (this EEP).

What belongs in a successful EEP?

Each EEP should have the following parts:

  1. Preamble -- RFC 822 style headers containing meta-data about the EEP, including the EEP number, a short descriptive title (limited to a maximum of 44 characters), the names, and optionally the contact info for each author, etc.

  2. Abstract -- a short (~200 word) description of the technical issue being addressed.

  3. Copyright/public domain -- Each EEP must either be explicitly labelled as placed in the public domain (see this EEP as an example) or licensed under the Open Publication License [7].

  4. Specification -- The technical specification should describe the syntax and semantics of any new language feature. The specification should be detailed enough to allow competing, interoperable implementations.

  5. Motivation -- The motivation is critical for EEPs that want to change the Erlang language. It should clearly explain why the existing language specification is inadequate to address the problem that the EEP solves. EEP submissions without sufficient motivation may be rejected outright.

  6. Rationale -- The rationale fleshes out the specification by describing what motivated the design and why particular design decisions were made. It should describe alternate designs that were considered and related work, e.g. how the feature is supported in other languages.

    The rationale should provide evidence of consensus within the community and discuss important objections or concerns raised during discussion.

  7. Backwards Compatibility -- All EEPs that introduce backwards incompatibilities must include a section describing these incompatibilities and their severity. The EEP must explain how the author proposes to deal with these incompatibilities. EEP submissions without a sufficient backwards compatibility treatise may be rejected outright.

  8. Reference Implementation -- The reference implementation must be completed before any EEP is given status "Final", but it need not be completed before the EEP is accepted. It is better to finish the specification and rationale first and reach consensus on it before writing code.

    The final implementation must include test code and documentation appropriate for either the Erlang language reference or the standard library reference.

EEP Formats and Templates

There are two EEP formats available to authors: plaintext and reStructuredText [8]. Both are UTF-8-encoded text files.

Plaintext EEPs are written with minimal structural markup that adheres to a rigid style. EEP 2 contains a instructions and a template [4] you can use to get started writing your plaintext EEP.

ReStructuredText [8] EEPs allow for rich markup that is still quite easy to read, but results in much better-looking and more functional HTML. EEP 3 contains instructions and a template [5] for reStructuredText EEPs.

There is a Python script that converts both styles of EEPs to HTML for viewing on the web [6]. Parsing and conversion of plaintext EEPs is self-contained within the script. reStructuredText EEPs are parsed and converted by Docutils [9] code called from the script.

EEP Header Preamble

Each EEP must begin with an RFC 822 style header preamble. The headers must appear in the following order. Headers marked with "*" are optional and are described below. All other headers are required.

  EEP: <eep number>
  Title: <eep title>
  Version: <svn version string>
  Last-Modified: <svn date string>
  Author: <list of authors' real names and optionally, email addrs>
* Discussions-To: <email address>
  Status: <Draft | Active | Accepted | Deferred | Rejected |
           Final | Replaced>
  Type: <Standards Track | Informational | Process>
* Content-Type: <text/plain | text/x-rst>
* Requires: <eep numbers>
  Created: <date created on, in dd-mmm-yyyy format>
* Erlang-Version: <version number>
  Post-History: <dates of postings to erlang-questions>
* Replaces: <eep number>
* Replaced-By: <eep number>

The Author header lists the names, and optionally the email addresses of all the authors/owners of the EEP. The format of the Author header value must be

Random J. User <address@dom.ain>

if the email address is included, and just

Random J. User

if the address is not given.

If there are multiple authors, each should be on a separate line following RFC 2822 continuation line conventions. Note that personal email addresses in EEPs will be obscured as a defense against spam harvesters.

While a EEP is in private discussions (usually during the initial Draft phase), a Discussions-To header will indicate the mailing list or URL where the EEP is being discussed. No Discussions-To header is necessary if the EEP is being discussed privately with the author, or on the erlang mailing list. Note that email addresses in the Discussions-To header will not be obscured.

The Type header specifies the type of EEP: Standards Track, Informational, or Process.

The format of a EEP is specified with a Content-Type header. The acceptable values are "text/plain" for plaintext EEPs (see EEP 2 [3]) and "text/x-rst" for reStructuredText EEPs (see EEP 3 [4]). Plaintext ("text/plain") is the default if no Content-Type header is present.

The Created header records the date that the EEP was assigned a number, while Post-History is used to record the dates of when new versions of the EEP are posted to erlang-questions. Both headers should be in dd-mmm-yyyy format, e.g. 14-Aug-2006.

Standards Track EEPs must have a Erlang-Version header which indicates the version of Erlang that the feature will be released with. Informational and Process EEPs do not need a Erlang-Version header.

EEPs may have a Requires header, indicating the EEP numbers that this EEP depends on.

EEPs may also have a Replaced-By header indicating that a EEP has been rendered obsolete by a later document; the value is the number of the EEP that replaces the current document. The newer EEP must have a Replaces header containing the number of the EEP that it rendered obsolete.

Auxiliary Files

EEPs may include auxiliary files such as diagrams. Such files must be named eep-XXXX-Y.ext, where "XXXX" is the EEP number, "Y" is a serial number (starting at 1), and "ext" is replaced by the actual file extension (e.g. "png").

Reporting EEP Bugs, or Submitting EEP Updates

How you report a bug, or submit a EEP update depends on several factors, such as the maturity of the EEP, the preferences of the EEP author, and the nature of your comments. For the early draft stages of the EEP, it's probably best to send your comments and changes directly to the EEP author. For more mature, or finished EEPs you may want to submit corrections to the erlang-patches mailing list.

When in doubt about where to send your changes, please check first with the EEP author and/or EEP editor.

EEP authors can update EEPs by submitting new versions to the editors.

Transferring EEP Ownership

It occasionally becomes necessary to transfer ownership of EEPs to a new champion. In general, we'd like to retain the original author as a co-author of the transferred EEP, but that's really up to the original author. A good reason to transfer ownership is because the original author no longer has the time or interest in updating it or following through with the EEP process, or has fallen off the face of the 'net (i.e. is unreachable or not responding to email). A bad reason to transfer ownership is because you don't agree with the direction of the EEP. We try to build consensus around a EEP, but if that's not possible, you can always submit a competing EEP.

If you are interested in assuming ownership of a EEP, send a message asking to take over, addressed to both the original author and the EEP editor <>. If the original author doesn't respond to email in a timely manner, the EEP editor will make a unilateral decision (it's not like such decisions can't be reversed :).

References and Footnotes

[1]We are very grateful to the Python community for devising such a good process for language revisions and for placing their documents in the public domain.
[2]PEP 1, PEP Purpose and Guidelines, Goodger, Hylton, Warsaw (
[3](1, 2) This svn server has not been setup yet but should be setup
[4](1, 2) EEP 2, Sample Plaintext EEP Template, Gustafsson (
[5]EEP 3, Sample reStructuredText EEP Template, Gustafsson (
[6]The script referred to here, which is a hack we need someone to make good tool support for EEPs and we also need an address for EEPs on the web.
[8](1, 2)