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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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