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From: Matt DeBoard
Subject: Re: SMIE
Date: Thu, 10 Jul 2014 00:22:44 -0400

One final question. In the case of e.g.

> Can't resolve the precedence cycle: .do < else:. < .do

What does the placement of the dots (left of "do", right of "else:") mean?

On Wed, Jul 9, 2014 at 11:02 PM, Stefan Monnier
<address@hidden> wrote:
>> Hi there. As the subject line says I’m writing for help with SMIE.
> Cool!
>> I am currently working on elixir-mode
>> <https://github.com/elixir-lang/emacs-elixir>, having (apparently) taking
>> over the mode as the latest in a line of contributors.
> I'd love to include this in GNU ELPA.  Interested?
>> Specifically I’m having trouble understanding the mental model for how
>> tokenisation & indentation works.  For example, in this
>> <https://github.com/elixir-lang/emacs-elixir/issues/18> issue, indentation
>> errors seem to crop up only after separating lines of code with blank
>> lines.
>> I have spent, seriously, hundreds of hours trying to sort out what’s
>> happening here and I am at my wits’ end.
> IIUC, Elixir syntax does not treat all whitespace as "irrelevant",
> contrary to the default tokenizer of SMIE.
>> Does this issue ring any bells with issues you’ve dealt with in
>> the past?
> Yes, indeed.  Octave and sh are two other languages that use SMIE and
> where some whitespace is syntactically significant.
> What you need to do is to change the tokenizer so that instead of
> skipping all whitespace, it turns the syntactically-significant
> whitespace into a token (you can name it any way you like; in the above
> languages, it turns out to be syntactically equivalent to a semi-colon,
> so we call it ";").
> I know absolutely nothing about Elixir or its syntax, so I can't give
> you specific details, but you can look at octave.el and sh-script.el
> for examples.  Feel free to email me back with more details if you need
> further help.
>> Final question, how is it determined if a token is a :list-intro token?
> Not sure I understand the question.  The issue is for the indentation
> rules, when it sees two (or more) concatenated expressions (e.g. "exp1
> exp2"), should it assume that exp2 is something like an argument to the
> exp1 function (and hence exp2 (and exp3, ...) should be indented like
> a function argument) or are all those "expressions" just a list, where
> the first is not more special than the second?
> This usually depends on the context.  E.g. in a situation like
>    fun x1 x2 x3 =>
> x2 is not an argument passed to the function x1;  Instead x1, x2, and x3
> are "siblings" and should be indented to the same level.  So to decide
> how to indent x2 and x3 w.r.t x1, SMIE calls the smie-rule-function with
> (:list-intro . "fun") so smie-rule-function can tell it that "fun"
> introduces a *list* of "things" rather than being followed by a "normal
> expression".
> Does that make more sense?
>> I have read the SMIE manual ten times, at least, but I’m really
>> struggling.  I would truly appreciate your help.
> I'm not very good at writing manuals, sorry.  But I promise to do my
> best to help you get SMIE working well.  In return, I would appreciate
> if you could help me improve the doc by giving, if not actual patches,
> at least suggestions of how to rewrite the doc, or what to add to it
> (usually, you can only make such suggestions after you finally
> understand what's going on, and at the same time it's
> important/necessary/useful to try and remember what it was that you
> didn't understand).
>         Stefan

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