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Out of those three I still prefer <% %>.  The main reason I like it is
familiarity.  Also the question mark makes me think of a wildcard, and I
don't want to use curly braces because of all the aforementioned reasons
(already has a meaning in YAML).

On Wed, Feb 18, 2015 at 3:07 PM, Dmitri Zimine <dzimine at stackstorm.com>
wrote:

> *Syntax options that we’d like to discuss **further *
>
> <% 1 + 1 %> # pro- ruby/js/puppet/chef familiarity con - spaces, and % is
> too large symbol
> <{1 + 1}>  # pro - less spaces, con - no familiarity
> <? 1 + 1 ?>  # php familiarity, need spaces
>
> The primary criteria to select these 3 options is that they are YAML
> compatible. Technically they all would solve our problems (primarily no
> embracing quotes needed like in Ansible so no ambiguity on data types).
>
> The secondary criteria is syntax symmetry. After all I agree with
> Patrick's point about better readability when we have opening and closing
> sequences alike.
>
>
> To me, another critical criteria is familiarity: target users - openstack
> developers and devops, familiar with the delimiters.
>
> That is why of the three above I prefer <% %> .
>
> It is commonly used in Puppet/Chef [1], Ruby, Javascript. One won’t be
> surprised to see it and won’t need to change the muscle memory to type
> open/closed characters especially when working on say Puppet and Mistral at
> the same time (not unlikely).
>
>
> [1]
> https://docs.puppetlabs.com/guides/templating.html#erb-is-plain-text-with-embedded-ruby
>
>
>
> On Feb 18, 2015, at 3:20 AM, Renat Akhmerov <rakhmerov at mirantis.com>
> wrote:
>
> Hi again,
>
> Sorry, I started writing this email before Angus replied so I will shoot
> it as is and then we can continue…
>
>
> So after discussing all the options again with a small group of team
> members we came to the following things:
>
> *Syntax options that we’d like to discuss **further *
>
> <% 1 + 1 %> # pro- ruby/js/puppet/chef familiarity con - spaces, and % is
> too large symbol
> <{1 + 1}>  # pro - less spaces, con - no familiarity
> <? 1 + 1 ?>  # php familiarity, need spaces
>
> The primary criteria to select these 3 options is that they are YAML
> compatible. Technically they all would solve our problems (primarily no
> embracing quotes needed like in Ansible so no ambiguity on data types).
>
> The secondary criteria is syntax symmetry. After all I agree with
> Patrick's point about better readability when we have opening and closing
> sequences alike.
>
> Some additional details can be found in [0]
>
>
> [0] https://etherpad.openstack.org/p/mistral-YAQL-delimiters
>
> Renat Akhmerov
> @ Mirantis Inc.
>
>
> On 18 Feb 2015, at 07:37, Patrick Hoolboom <patrick at stackstorm.com> wrote:
>
>  My main concern with the {} delimiters in YAQL is that the curly brace
> already has a defined use within YAML.  We most definitely will eventually
> run in to parsing errors with whatever delimiter we choose but I don't feel
> that it should conflict with the markup language it is directly embedded
> in.  It gets quite difficult to, at a glance, identify YAQL expressions.
>  <% %> may appear ugly to some but I feel that it works as a clear
> delimiter of both the beginning AND the end of the YAQL query. The options
> that only escape the beginning look fine in small examples like this but
> the workflows that we have written or seen in the wild tend to have some
> fairly large expressions.  If the opening and closing delimiters don't
> match, it gets quite difficult to read.
>
>>
>> *From: *Anastasia Kuznetsova <akuznetsova at mirantis.com>
>> *Subject: **Re: [openstack-dev] [Mistral] Changing "expression"
>> delimiters in Mistral DSL*
>> *Date: *February 17, 2015 at 8:28:27 AM PST
>> *To: *"OpenStack Development Mailing List (not for usage questions)" <
>> openstack-dev at lists.openstack.org>
>> *Reply-To: *"OpenStack Development Mailing List \(not for usage
>> questions\)" <openstack-dev at lists.openstack.org>
>>
>> As for me, I think that <% ... %> is not an elegant solution and looks
>> massive because of '%' sign. Also I agree with Renat, that <% ... %>
>> reminds HTML/Jinja2 syntax.
>>
>> I am not sure that similarity with something should be one of the main
>> criteria, because we don't know who will use Mistral.
>>
>> I like:
>> - <{1 + $.var}> Renat's example
>> - variant with using some functions (item 2 in Dmitry's list):  { yaql:
>> “1+1+$.my.var < 100” } or <yaql: 'Hello' + $.name >
>> - my two cents, maybe we can use something like: result: -< "Hello" +
>> $.name >-
>>
>>
>> Regards,
>> Anastasia Kuznetsova
>>
>> On Tue, Feb 17, 2015 at 1:17 PM, Nikolay Makhotkin <
>> nmakhotkin at mirantis.com> wrote:
>>
>>> Some suggestions from me:
>>>
>>> 1. <y 1 + $.var > # (short from yaql).
>>> 2. <{ 1 + $.var }>  # as for me, looks more elegant than <% %>. And
>>> visually it is more strong
>>>
>>> A also like p7 and p8 suggested by Renat.
>>>
>>> On Tue, Feb 17, 2015 at 11:43 AM, Renat Akhmerov <rakhmerov at mirantis.com
>>> > wrote:
>>>
>>>> One more:
>>>>
>>>> p9: \{1 + $.var} # That’s pretty much what
>>>> https://review.openstack.org/#/c/155348/ addresses but it’s not
>>>> exactly that. Note that we don’t have to put it in quotes in this case to
>>>> deal with YAML {} semantics, it’s just a string
>>>>
>>>>
>>>>
>>>> Renat Akhmerov
>>>> @ Mirantis Inc.
>>>>
>>>>
>>>>
>>>> On 17 Feb 2015, at 13:37, Renat Akhmerov <rakhmerov at mirantis.com>
>>>> wrote:
>>>>
>>>> Along with <% %> syntax here are some other alternatives that I checked
>>>> for YAML friendliness with my short comments:
>>>>
>>>> p1: ${1 + $.var}     # Here it’s bad that $ sign is used for two
>>>> different things
>>>> p2: ~{1 + $.var}     # ~ is easy to miss in a text
>>>> p3: ^{1 + $.var}     # For someone may be associated with regular
>>>> expressions
>>>> p4: ?{1 + $.var}
>>>> p5: <{1 + $.var}> # This is kinda crazy
>>>> p6: e{1 + $.var} # That looks a pretty interesting option to me, “e”
>>>> could mean “expression” here.
>>>> p7: yaql{1 + $.var} # This is interesting because it would give a
>>>> clear and easy mechanism to plug in other expression languages, “yaql” here
>>>> is a used dialect for the following expression
>>>> p8: y{1 + $.var} # “y” here is just shortened “yaql"
>>>>
>>>>
>>>> Any ideas and thoughts would be really appreciated!
>>>>
>>>> Renat Akhmerov
>>>> @ Mirantis Inc.
>>>>
>>>>
>>>>
>>>> On 17 Feb 2015, at 12:53, Renat Akhmerov <rakhmerov at mirantis.com>
>>>> wrote:
>>>>
>>>> Dmitri,
>>>>
>>>> I agree with all your reasonings and fully support the idea of changing
>>>> the syntax now as well as changing system’s API a little bit due to
>>>> recently found issues in the current engine design that don’t allow us, for
>>>> example, to fully implement ‘with-items’ (although that’s a little bit
>>>> different story).
>>>>
>>>> Just a general note about all changes happening now: *Once we release
>>>> kilo stable release our API, DSL of version 2 must be 100% stable*. I
>>>> was hoping to stabilize it much earlier but the start of production use
>>>> revealed a number of things (I think this is normal) which we need to
>>>> address, but not later than the end of Kilo.
>>>>
>>>> As far as <% %> syntax. I see that it would solve a number of problems
>>>> (YAML friendliness, type ambiguity) but my only not strong argument is that
>>>> it doesn’t look that elegant in YAML as it looks, for example, in ERB
>>>> templates. It really reminds me XML/HTML and looks like a bear in a grocery
>>>> store (tried to make it close to one old russian saying :) ). So just for
>>>> this only reason I’d suggest we think about other alternatives, maybe not
>>>> so familiar to Ruby/Chef/Puppet users but looking better with YAML and at
>>>> the same time being YAML friendly.
>>>>
>>>> I would be good if we could here more feedback on this, especially from
>>>> people who started using Mistral.
>>>>
>>>> Thanks
>>>>
>>>> Renat Akhmerov
>>>> @ Mirantis Inc.
>>>>
>>>>
>>>>
>>>> On 17 Feb 2015, at 03:06, Dmitri Zimine <dzimine at stackstorm.com> wrote:
>>>>
>>>> SUMMARY:
>>>> ----------------
>>>>
>>>> We are changing the syntax for inlining YAQL expressions in Mistral
>>>> YAML from {1+$.my.var} (or “{1+$.my.var}”) to <% 1+$.my.var %>
>>>>
>>>> Below I explain the rationale and the criteria for the choice. Comments
>>>> and suggestions welcome.
>>>>
>>>> DETAILS:
>>>> -------------
>>>>
>>>> We faced a number of problems with using YAQL expressions in Mistral
>>>> DSL: [1] must handle any YAQL, not only the ones started with $; [2] must
>>>> preserve types and [3] must comply with YAML. We fixed these problems by
>>>> applying Ansible style syntax, requiring quotes around delimiters (e.g.
>>>> “{1+$.my.yaql.var}”). However, it lead to unbearable confusion in DSL
>>>> readability, in regards to types:
>>>>
>>>>     publish:
>>>>        intvalue1: "{1+1}” # Confusing: you expect quotes to be string.
>>>>        intvalue2: "{int(1+1)}” # Even this doestn’ clean the confusion
>>>>        whatisthis:"{$.x + $.y}” # What type would this return?
>>>>
>>>> We got a very strong push back from users in the filed on this syntax.
>>>>
>>>> The crux of the problem is using { } as delimiters YAML. It is plain
>>>> wrong to use the reserved character. The clean solution is to find a
>>>> delimiter that won’t conflict with YAML.
>>>>
>>>> Criteria for selecting best alternative are:
>>>> 1) Consistently applies to to all cases of using YAML in DSL
>>>> 2) Complies with YAML
>>>> 3) Familiar to target user audience - openstack and devops
>>>>
>>>> We prefer using two-char delimiters to avoid requiring extra escaping
>>>> within the expressions.
>>>>
>>>> The current winner is <% %>. It fits YAML well. It is familiar to
>>>> openstack/devops as this is used for embedding Ruby expressions in Puppet
>>>> and Chef (for instance, [4]). It plays relatively well across all cases of
>>>> using expressions in Mistral (see examples in [5]):
>>>>
>>>> ALTERNATIVES considered:
>>>> --------------------------------------------------
>>>>
>>>> 1) Use Ansible-like syntax:
>>>> http://docs.ansible.com/YAMLSyntax.html#gotchas
>>>> Rejected for confusion around types. See above.
>>>>
>>>> 2) Use functions, like Heat HOT or TOSCA:
>>>>
>>>> HOT templates and TOSCA doesn’t seem to have a concept of typed
>>>> variables to borrow from (please correct me if I missed it). But they have
>>>> functions: function: { function_name: {foo: [parameter1, parameter 2],
>>>> bar:"xxx”}}. Applied to Mistral, it would look like:
>>>>
>>>>     publish:
>>>>      - bool_var: { yaql: “1+1+$.my.var < 100” }
>>>>
>>>> Not bad, but currently rejected as it reads worse than delimiter-based
>>>> syntax, especially in simplified one-line action invocation.
>>>>
>>>> 3) < > paired with other symbols: php-styoe  <? ..?>
>>>>
>>>>
>>>> *REFERENCES: *
>>>> ----------------------
>>>>
>>>> [1] Allow arbitrary YAQL expressions, not just ones started with $ :
>>>> https://github.com/stackforge/mistral/commit/5c10fb4b773cd60d81ed93aec33345c0bf8f58fd
>>>> [2] Use Ansible-like syntax to make YAQL expressions YAML complient
>>>> https://github.com/stackforge/mistral/commit/d9517333b1fc9697d4847df33d3b774f881a111b
>>>> [3] Preserving types in YAQL
>>>> https://github.com/stackforge/mistral/blob/d9517333b1fc9697d4847df33d3b774f881a111b/mistral/tests/unit/test_expressions.py#L152-L184
>>>> [4]Using <% %> in Puppet
>>>> https://docs.puppetlabs.com/guides/templating.html#erb-is-plain-text-with-embedded-ruby
>>>>
>>>> [5] Etherpad with discussion
>>>> https://etherpad.openstack.org/p/mistral-YAQL-delimiters
>>>> [6] Blueprint
>>>> https://blueprints.launchpad.net/mistral/+spec/yaql-delimiters
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
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>>>>
>>>
>>>
>>> --
>>> Best Regards,
>>> Nikolay
>>>
>>>
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