[erlang-questions] Indentation of multiline strings

Bengt Kleberg <>
Mon Feb 10 08:01:12 CET 2014


Greetings,

One reason against a standalone formatter is that it could introduce
bugs in the code. That this is only a problem with a standalone
formatter is probably based upon that nobody would use a editor based
formatter and then not compile/test after wards.

To make a stand alone formatter with better level of confidence I
suggest using Erlang/OTP tools to create one of the intermediate level
formats (Core Erlang, "parse trees", the simplest/quickest/...) that
removes formatting. If this is done before and after the standalone
formatting, and the result is the same, then no bugs have been
introduced.


bengt

On Fri, 2014-02-07 at 17:19 +0100, Vlad Dumitrescu wrote:
> On Fri, Feb 7, 2014 at 4:27 PM, Steve Vinoski <> wrote:
> > First, let's assume there's general agreement in the community that emacs
> > erlang-mode is the de facto standard for erlang code formatting, and is thus
> > the starting point for developing a formatting specification. I believe
> > you're basing your work on this assumption, Vlad, and if so I agree with
> > that approach, but if not please correct me.
> 
> That's correct.
> 
> > Some might object to using
> > erlang-mode as the starting point on the basis that other editors sometimes
> > have a hard time formatting code the same way erlang-mode does, but I
> > believe most of the OTP team and most of the Erlang community uses emacs and
> > erlang-mode, so I view it as the most practical starting point.
> 
> Other editors will still have to implement a formatter/indenter. I
> think the issues they have today are mostly related to mixing tabs and
> spaces, but since Anthony said that his patches only have spaces and
> there were no issues, that would simplify it.
> 
> > To create a formatting specification, I recommend that if you haven't done
> > so already, start collecting cases like the multiline string and binary
> > cases where erlang-mode fails, and report them as bugs against erlang-mode.
> > Obviously this applies to anyone who wishes to help.
> 
> I think that I will start by specifying how erlang-mode indents today.
> That would be mostly a case of looking at the test file in the sources
> and extract the data by inspection. The vision is to not only specify
> an indenter, but even a pretty printer. Here I must credit Tuncer for
> starting a discussion with me for a couple of weeks ago.
> 
> > To resolve those bugs, we may need to form a small group that can decide how
> > erlang-mode should format the problematic cases. A good choice for
> > volunteers here are the primary erlang-mode maintainer and some willing
> > subset of those who have recently contributed code and patches to
> > erlang-mode. As one of those people, I'm willing to help with that, and also
> > willing to help resolve the bugs in erlang-mode so it conforms to the
> > specification you're putting together.
> 
> Great, thanks!
> 
> > I assume that during this effort someone -- probably you Vlad, but I know of
> > other parties also interested -- would be writing a new tool that also
> > conforms to the formatting specification. Having such a tool would give us
> > at least two independent implementations of the spec.
> 
> Yes, it would be useful to have an Erlang-based tool too. I can use it
> from erlide, so I don't need to write anything in Java.
>  /Vlad
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