One more:
p9: \{1 + $.var} # That’s pretty much what
https://review.openstack.org/#/c/155348/
<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 <[email protected]> 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 + $.var} # “y” here is just shortened “yaql"
>
>
> Any ideas and thoughts would be really appreciated!
>
> Renat Akhmerov
> @ Mirantis Inc.
>
>
>
>> On 17 Feb 2015, at 12:53, Renat Akhmerov <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> Dmitri,
>>
>> I agree with all your reasonings and fully support the idea of changing the
>> syntax now as well as changing system’s API a little bit due to recently
>> found issues in the current engine design that don’t allow us, for example,
>> to fully implement ‘with-items’ (although that’s a little bit different
>> story).
>>
>> Just a general note about all changes happening now: Once we release kilo
>> stable release our API, DSL of version 2 must be 100% stable. I was hoping
>> to stabilize it much earlier but the start of production use revealed a
>> number of things (I think this is normal) which we need to address, but not
>> later than the end of Kilo.
>>
>> As far as <% %> syntax. I see that it would solve a number of problems (YAML
>> friendliness, type ambiguity) but my only not strong argument is that it
>> doesn’t look that elegant in YAML as it looks, for example, in ERB
>> templates. It really reminds me XML/HTML and looks like a bear in a grocery
>> store (tried to make it close to one old russian saying :) ). So just for
>> this only reason I’d suggest we think about other alternatives, maybe not so
>> familiar to Ruby/Chef/Puppet users but looking better with YAML and at the
>> same time being YAML friendly.
>>
>> I would be good if we could here more feedback on this, especially from
>> people who started using Mistral.
>>
>> Thanks
>>
>> Renat Akhmerov
>> @ Mirantis Inc.
>>
>>
>>
>>> On 17 Feb 2015, at 03:06, Dmitri Zimine <[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>> SUMMARY:
>>> ----------------
>>>
>>> We are changing the syntax for inlining YAQL expressions in Mistral YAML
>>> from {1+$.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 + $.y}” # What type would this return?
>>>
>>> We got a very strong push back from users in the filed on this syntax.
>>>
>>> The crux of the problem is using { } as delimiters YAML. It is plain wrong
>>> to use the reserved character. The clean solution is to find a delimiter
>>> that won’t conflict with YAML.
>>>
>>> Criteria for selecting best alternative are:
>>> 1) Consistently applies to to all cases of using YAML in DSL
>>> 2) Complies with YAML
>>> 3) Familiar to target user audience - openstack and devops
>>>
>>> We prefer using two-char delimiters to avoid requiring extra escaping
>>> within the expressions.
>>>
>>> The current winner is <% %>. It fits YAML well. It is familiar to
>>> openstack/devops as this is used for embedding Ruby expressions in Puppet
>>> and Chef (for instance, [4]). It plays relatively well across all cases of
>>> using expressions in Mistral (see examples in [5]):
>>>
>>> ALTERNATIVES considered:
>>> --------------------------------------------------
>>>
>>> 1) Use Ansible-like syntax: http://docs.ansible.com/YAMLSyntax.html#gotchas
>>> <http://docs.ansible.com/YAMLSyntax.html#gotchas>
>>> Rejected for confusion around types. See above.
>>>
>>> 2) Use functions, like Heat HOT or TOSCA:
>>>
>>> HOT templates and TOSCA doesn’t seem to have a concept of typed variables
>>> to borrow from (please correct me if I missed it). But they have functions:
>>> function: { function_name: {foo: [parameter1, parameter 2], bar:"xxx”}}.
>>> Applied to Mistral, it would look like:
>>>
>>> publish:
>>> - bool_var: { yaql: “1+1+$.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
>>>
>>> <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
>>>
>>> <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
>>>
>>> <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
>>>
>>> <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
>>> <https://etherpad.openstack.org/p/mistral-YAQL-delimiters>
>>> [6] Blueprint
>>> https://blueprints.launchpad.net/mistral/+spec/yaql-delimiters
>>> <https://blueprints.launchpad.net/mistral/+spec/yaql-delimiters>
>>>
>>
>
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