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From Alex Heneveld <>
Subject Re: [PROPOSAL] Brooklyn DSL in YAML using custom YAML types
Date Sat, 30 Jul 2016 11:07:02 GMT

Hi Thomas-

 > I get that it could be handy to use our YAML as JSON. Do you have any 
examples of this
 > kind of use within the Brooklyn ecosystem?

There are quite a few places this is done including when you deploy, the 
first-pass parse at the Brooklyn server.  It's a second pass interprets 
$brooklyn:... as strings within the "jsonable" object (where I use that 
term to describe a primitive, string, null, or list of jsonables, or map 
with string keys and jsonable values).

There are also some graphical renderers/editors of blueprints which do 
this -- with limited support for $brooklyn DSL strings/maps, but because 
tools can simply treat them as jsonable objects it isn't a problem.  
Svet describes some he has done, and I'd like to keep it easy for others.

While I like the ! capability of YAML to express types I worry that (a) 
it is not widely understood and would make the blueprints harder for 
people to read, and (b) it implies some knowledge of the type implied by 
! in order to represent the object even on a first parse.

In short by preserving `$brooklyn:...` and `type: xxx` as stings on a 
first class parse -- in other words by sticking with the JSON-isomorphic 
subset -- the first-pass parse model becomes much simpler and easier for 
external tools to work with.

I also question your claim that our YAML is hacky or non-compliant.  The 
YAML spec 7.3.3 says:

 > Plain scalars must never contain the “: ” and “ #” character 
combinations. Such combinations would cause
 > ambiguity with mapping key: value pairs and comments. In addition, 
inside flow collections, or when used as
 > implicit keys, plain scalars must not contain [127] [128] [129] [130] 
the “[”, “]”, “{”, “}” and “,” characters.

By my reading there is no restriction on an initial $ or intermediate 
commas or quotes (as long as you aren't in a bracketed list) so the 
example you give is valid YAML whether plain or single quoted, or double 
quoted with double quotes escaped.  The YML spec example 7.10 includes 
as examples:

- Up up, and away!

Re wrapping it in quotes, you write:

 > this is an issue for the Brooklyn parser as the value will be treated 
as a `String`
 > and not as a `DslCommand` object.

Pretty certain this is not that case.  You can wrap in quotes fine (or 
indeed supply JSON which does this).  The server expects '$brooklyn:...' 
as a string, with the type conversion handled as a second pass.  A 
client does not need to know anything about the "DslCommand" library.

I know that some parsers eagerly quote but most will also generously 
parse if the input is unambiguous, but that isn't often an issue and 
where it is I think we can work around that by requesting that the 
Brooklyn server return strict JSON rather than YAML (or try to patch the 
buggy YAML library).

If you've got some specific parser issues share them -- that will be 
interesting -- but I've had good experiences YAML-parsing with Node, Go, 
and Ruby (although the Ruby one is a bit idiosyncratic).


On 29/07/2016 16:03, Thomas Bouron wrote:
> @Alex, @Svet, @Andrew: I get that it could be handy to use our YAML as
> JSON. Do you have any examples of this kind of use within the Brooklyn
> ecosystem?
> If not, this is not a compelling argument to me because again, our YAML is
> currently not valid: we shouldn't use any `$brooklyn:(.+)` as key if it is
> unwrapped. The example given by Andrew is the perfect example this issue:
> Brooklyn will not complain and process the blueprint whereas any other
> parser will reject it (which was why I made this proposal in the first
> place)
> On Fri, 29 Jul 2016, 13:52 Svetoslav Neykov, <
>> wrote:
>> Agree with that. Something I wrote a couple of hours ago while offline, so
>> didn't see Alex's email:
>> Something to have in mind when discussing this - YAML is a superset of
>> JSON as all of you are well aware. Today we can express the Brooklyn CAMP
>> spec completely in JSON and it will just work. I've actually taken
>> advantage of this in browser clients, using the built-in JSON support to
>> convert objects in memory to markup, without needing to pull in any
>> external libraries.
>> Svet.
>>> On 29.07.2016 г., at 9:54, Alex Heneveld <
>>> wrote:
>>> The ability to switch between json and yaml (so we only use the
>>> json-isomorphic subset) is nice for working with models eg is js in the
>>> browser, and feels less intimidating to new people. I'd like anywhere we
>>> use !! to be optional. (if it were a more widely used part of yaml I
>> might
>>> think differently).
>>> Best
>>> Alex
>>> On 29 Jul 2016 03:35, "Andrew Kennedy" <
>>> wrote:
>>>> Hi.
>>>> The 'formatString' example you quote would normally be written like
>> this,
>>>> though:
>>>>   brooklyn.config:
>>>>     brooklyn.example.db.url:
>>>>       $brooklyn:formatString:
>>>>         - "jdbc:%s%s?user=%s\\&password=%s"
>>>>         - $brooklyn:component("db").attributeWhenReady("datastore.url")
>>>>         - "visitors"
>>>>         - "brooklyn"
>>>>         - "br00k11n"
>>>> So, I'm not sure what we gain here? I'll have a proper look at the YAML
>>>> spec, though, and see if I can understand it better.
>>>> Cheers,
>>>> Andrew.
>>>> On Wed, 13 Jul 2016 at 13:35 Thomas Bouron <
>>>> wrote:
>>>>> Hi All
>>>>> The YAML spec[1] has a very nice and standard way of defining custom
>>>> types
>>>>> by prefixing any value or object by a `!!<type_name>`. This seems
>> a
>>>>> perfect feature for the Brooklyn DSL instead of the
>>>> `$brooklyn:<command>`.
>>>>> Let's me explain why.
>>>>> Right now, a Brooklyn DSL command needs to be written as a string such
>>>> as:
>>>>> $brooklyn:formatString("jdbc:%s%s?user=%s\\&password=%s",
>>>>> component("db").attributeWhenReady("datastore.url"),
>>>>> "visitors", "brooklyn", "br00k11n")
>>>>> However, any good YAML library (such as js-yaml[2]) to parse and dump
>>>> YAML
>>>>> <--> JSON would wrap this string in quotes because it contains
>> or
>>>>> reserved characters. That is the expected behaviour based on the
>>>>> specification[3]. But this is an issue for the Brooklyn parser as the
>>>> value
>>>>> will be treated as a `String` and not as a `DslCommand` object.
>>>>> So my proposal is as follow: support the Brooklyn DSL as a standard
>>>> custom
>>>>> YAML type. We obviously need to avoid any quote or reserved characters.
>>>>> That is relatively simple for commands that takes only one parameter,
>> for
>>>>> instance:
>>>>>    - $brooklyn:component('my-id') could become
>>>>>       - !brooklyn:component my-id
>>>>>    - $brooklyn:entitySpec would become
>>>>>       - !brooklyn:spec
>>>>> For the more complex ones, I created a gist[4] that illustrates how
>> this
>>>>> could work. It is more verbose than the current version but we get a
>> rid
>>>> of
>>>>> the hacky `$brooklyn` and comply fully to the YAML specification.
>>>>> Best.
>>>>> [1]
>>>>> [2]
>>>>> [3]
>>>>> [4]
>>>>> --
>>>>> Thomas Bouron • Software Engineer @ Cloudsoft Corporation •
>>>>> Github:
>>>>> Twitter:
>>>> --
>>>> Andrew Kennedy ; Founder project ; @grkvlt ; Cloudsoft
>> --
> Thomas Bouron • Software Engineer @ Cloudsoft Corporation •
> Github:
> Twitter:

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