[erlang-questions] Erlang documentation -- a modest proposal

Joe Armstrong <>
Fri Sep 23 10:13:38 CEST 2016

I have a few comments about the documentation:

This answers a few question that keep arising, and has a few of my own

Q: Who was the documentation written for?

A: Ericsson Internal usage

   The original documentation made the following assumptions

   - The readers would be internal Ericsson programmers who knew Erlang
   - If the programmers had a problem understanding things they would ask
     us directly

   So we favored a terse declarative style

Q: How is the documentation structured
A: It's all in XML

   The idea was that all documentation would be generated from the XML
   There are current about 1000 XML files containing about 10MB of text

   The XML sources are in the distribution source tree.
   So for example the documentation for lists.erl is in the file
   <Dir>/lib/stdlib/doc/src/lists.xml (<Dir> is where the system was unpacked)

Q: How is the documentation produced
A: Programmatically

   Various programs munge the XML inputs (and the sources) trying to make
   web-sites and PDF

   We could use some help here - really - the PDF is produced with
some XSLT magic
   and the web site with goodness knows what.

So what's wrong and what could we do?

1) Things are not beautiful

   I agree - the documentation is not typographically beautiful

   Personally I like PDF - I took a look and found this:


   It would be nice to transform the documentation into this form
   for printing and reading

2) The HTML documentation could be improved and made more interactive

   I have at various times written 'erl_to_html' that makes HTML pages out of
   erlang - it would be nice to browse your own code, clicking on function names
   to follow the code or to unfold the documentation.

   On-line documentation can have things like type spec in hidden folds
   which open in place when you click on them. Or possibly a tiddly-wiki like

   http://tiddlywiki.com/ might inspire a new interface

3) There is no official proof-reading quality control mechanism

   I tried on several occasions to hire a technical author - management always
   views this as a waste of money - so this never happened.

   Most of the documentation is written by people who are not
   native English speakers. They could use some help.

   By contract my Erlang book had

     - Me (who wrote it)
     - Dave Thomas (my editor) (he was great)
     - A Proof Reader (By proof reader I mead one of these super-human beings
       who can spot a spelling error at 10,000 meters from your text,
       while reading upside down by candle light
     - An Indexer (did you know there were professional Indexers?)
     - A typographer (who worried about

   Have you every heard *anybody* complaining about widows and orphans
   in the Erlang printed documentation? I had to rephrase several
   paragraphs to avoid nasty widows and orphans.

4) There are no examples

   I agree there should be zillions of examples.

   Rather than adding them to the existing XML tree I'd propose a new
   DTD for examples which could be cross-linked into the

5) There are no construction examples

   Examples show "the finished work" but not "how you got there"

   In my book I often shown really short functions in 10 lines or so
   of code.  But I don't discuss how I got to those ten lines.

   I show the 10 lines and explain what each lines does.

   I do not explain how I wrote the first line - I might have googled
   a bit done some research. In a 50 line program I'll probably have
   tested it as I grew it - testing 10 lines at a time.

   How we grow programs from small seeds is not explained.

6) The barrier for entry for fixing a typo is HUGE

   If I see a typo (a simple spelling error) in the on-line documentation
   the barrier of entry for fixing it is HUGE (sorry for SHOUTING).

   Download the entire distribution - unpack (240 MBytes) find the
   typo (where the heck is it?) - fix it - make a push request ....

   Do I really have to download hundreds of Megabytes to fix a one
   character typo?

   I keep pointing people to the web site for "real world Haskell"

   The barrier for entry to fixing a mistake in the text is minimal.
   I actually like the RWH model - the reader adds a comment, the author fixes
   the bug.

   When writing books I would not like other people fixing my typos, I
   want many eyes to help be find the typos - then I'll fix them? Why
   is this? Because I'm ultimately responsible for what I write -
   Sometimes (not often) I might want to totally rewrite a section
   based on a single typo.

   If somebody could figure out how to automate fixing typos it would be great.
   [the problem is to find the XML that needs to be edited, given that the error
    was found in a generated document - I guess if each paragraph has
a hidden GUID
    <<WHICH I'VE BEEN RANTING ON ABOUT FOR YEARS>> it would be trivial]

   <aside>All paragraphs should have GUIDs and be stored in a global content
   adressable store (why GUIDs? - we could use the SHA as a key but
they we could not
   edit the paragraph :-) </aside>

7) The erlang mailing list has loads of examples

   The erlang mailing list has thousands of useful examples
   but they are not extracted, edited sorted and classified.

   There are issues of copyright and attribution here - but I think
   it would be useful to extract some of the better postings to this list
   and move them into the documentation tree.

Making beautiful readable useful documentation is very difficult and
needs love care and attention to detail - it's an unappreciated form
of literature.

On Fri, Sep 23, 2016 at 8:40 AM, Loïc Hoguin <> wrote:
> On 09/23/2016 05:18 AM, Kenneth Lakin wrote:
>> Speaking of the User's Guide... -ideally- someone with no Erlang
>> experience should first be reading the Reference Manual User's Guide
>> along with the Getting Started Guide (or LYSE or something) to pick up
>> the fundamentals, rather than the various module Reference Manuals. In
>> my experience, reference manuals exist to quickly provide useful
>> information to people who are already familiar with a language. They
>> shouldn't be language primers, as primers serve another purpose and
>> should be in another document.
> That's the thing: you have no control over what document people will read
> first. You also have no control over what people will *remember*.
> When first coming to the language, most people will
> forget/misremember/misunderstand most of what they read until they get some
> practice; and that's when a good function reference with all details and
> examples is helpful.
> --
> Loïc Hoguin
> http://ninenines.eu
> Author of The Erlanger Playbook,
> A book about software development using Erlang
> _______________________________________________
> erlang-questions mailing list
> http://erlang.org/mailman/listinfo/erlang-questions

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