MF2 delimiters/sigils and YAML/Ruby on Rails

[duerst]

I have been thinking about, and working together with a student of mine, on trying to use MF2 with Ruby on Rails. One problematic area I have found is that there are some conflicts between currently used/planned syntax characters in MF2 and in YAML, in particular '#' and '{'.

This raises serious questions, at least for me, whether '{', '{{', and '#', are really good choices for our syntax. I have to admit that I can't propose any alternatives at the moment because I don't know YAML well enough. But I can easily check out other proposals.

TL;DR

Ruby on Rails uses YAML to store resource strings. See https://guides.rubyonrails.org/i18n.html for a general explanation, and e.g. https://github.com/redmine/redmine/blob/master/config/locales for examples.

In YAML, strings can be written bare, without any kinds of quotes,...
(see https://github.com/redmine/redmine/blob/master/config/locales/en.yml#L155).

On the other hand, YAML uses various characters to indicate constructs other than strings.

In particular, '#' introduces comments (as it does in many scripting languages including Python, Ruby, and various shell languages).

Also, '{' starts a hash/map/dictionary, similar again to Python, Ruby, JavaScript, JSON and so on.

Below are examples of some one-liners in YAML (between >>> and <<<) and the resulting objects on the next line (strings in "", which is what we would want; others like hash/map/dictionary (in {}) are not what we want). There are even some cases where an error is produced.

>>>--- foo #cdef<<<
"foo"

>>>--- {abc}<<<
{"abc"=>nil}

>>>--- {{abc}}<<<
{{"abc"=>nil}=>nil}

>>>--- abc {#def} ghi<<<
"abc {#def} ghi"

>>>--- abc #{def} ghi<<<
"abc"

>>>--- abc {$def} ghi<<<
"abc {$def} ghi"

>>>--- {{#match}}<<<
!!!!! This errors out!

And here's the Ruby program that generate the above, just for your reference (with comments for non-Rubyists):

require 'yaml'                    # use 'yaml' library, based on libyaml
examples = ["--- foo #cdef",      # array of YAML examples
            "--- {abc}",
            "--- {{abc}}",
            "--- abc {#def} ghi",
            '--- abc #{def} ghi',
            '--- abc {$def} ghi',
            "--- {{#match}}",
           ]
examples.each do |ex|             # iterate over 'examples' array
  puts ('>>>'+ex+'<<<')           # print example
  begin
    s = YAML.load(ex)             # parse as YAML
  rescue
    puts "!!!!! This errors out!" # handle error case
  else
    puts s.inspect                # print resulting object
  end
  puts                            # print empty line as separator
end

[aphillips]

Related to #521

[aphillips]

The syntax adopted . as the function starter and removed the {{/}} around the message. Does this address this issue?

[duerst]

The syntax adopted . as the function starter and removed the {{/}} around the message. Does this address this issue?

Yes. It does. Thanks, closing.