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 + $.var} # “y” here is just shortened “yaql"
Any ideas and thoughts would be really appreciated!
Renat Akhmerov
@ Mirantis Inc.
> On 17 Feb 2015, at 12:53, Renat Akhmerov <[email protected]> wrote:
>
> Dmitri,
>
> I agree with all your reasonings and fully support the idea of changing the
> syntax now as well as changing system’s API a little bit due to recently
> found issues in the current engine design that don’t allow us, for example,
> to fully implement ‘with-items’ (although that’s a little bit different
> story).
>
> Just a general note about all changes happening now: Once we release kilo
> stable release our API, DSL of version 2 must be 100% stable. I was hoping to
> stabilize it much earlier but the start of production use revealed a number
> of things (I think this is normal) which we need to address, but not later
> than the end of Kilo.
>
> As far as <% %> syntax. I see that it would solve a number of problems (YAML
> friendliness, type ambiguity) but my only not strong argument is that it
> doesn’t look that elegant in YAML as it looks, for example, in ERB templates.
> It really reminds me XML/HTML and looks like a bear in a grocery store (tried
> to make it close to one old russian saying :) ). So just for this only reason
> I’d suggest we think about other alternatives, maybe not so familiar to
> Ruby/Chef/Puppet users but looking better with YAML and at the same time
> being YAML friendly.
>
> I would be good if we could here more feedback on this, especially from
> people who started using Mistral.
>
> Thanks
>
> Renat Akhmerov
> @ Mirantis Inc.
>
>
>
>> On 17 Feb 2015, at 03:06, Dmitri Zimine <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> SUMMARY:
>> ----------------
>>
>> We are changing the syntax for inlining YAQL expressions in Mistral YAML
>> from {1+$.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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