<html><head><meta http-equiv="Content-Type" content="text/html charset=windows-1252"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Along with <% %> syntax here are some other alternatives that I checked for YAML friendliness with my short comments:<div class=""><br class=""></div><div class=""><div class="">p1: ${1 + $.var} <span class="Apple-tab-span" style="white-space:pre"> </span># Here it’s bad that $ sign is used for two different things</div><div class="">p2: ~{1 + $.var} <span class="Apple-tab-span" style="white-space:pre"> </span># ~ is easy to miss in a text</div><div class="">p3: ^{1 + $.var} <span class="Apple-tab-span" style="white-space:pre"> </span># For someone may be associated with regular expressions</div><div class="">p4: ?{1 + $.var}<span class="Apple-tab-span" style="white-space:pre"> </span></div><div class="">p5: <{1 + $.var}><span class="Apple-tab-span" style="white-space:pre"> </span># This is kinda crazy</div><div class="">p6: e{1 + $.var}<span class="Apple-tab-span" style="white-space:pre"> </span># That looks a pretty interesting option to me, “e” could mean “expression” here.</div><div class="">p7: yaql{1 + $.var}<span class="Apple-tab-span" style="white-space:pre"> </span># 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</div><div class="">p8: y{1 + $.var}<span class="Apple-tab-span" style="white-space:pre"> </span># “y” here is just shortened “yaql"</div><div class=""><br class=""></div><div class=""><br class=""></div><div class="">Any ideas and thoughts would be really appreciated!</div><div class=""><br class=""></div><div class="">
<div class="">Renat Akhmerov</div><div class="">@ Mirantis Inc.</div><div class=""><br class=""></div><br class="Apple-interchange-newline">
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<br class=""><div><blockquote type="cite" class=""><div class="">On 17 Feb 2015, at 12:53, Renat Akhmerov <<a href="mailto:rakhmerov@mirantis.com" class="">rakhmerov@mirantis.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=windows-1252" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Dmitri,<div class=""><br class=""></div><div class="">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).</div><div class=""><br class=""></div><div class="">Just a general note about all changes happening now: <b class="">Once we release kilo stable release our API, DSL of version 2 must be 100% stable</b>. 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.</div><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class="">I would be good if we could here more feedback on this, especially from people who started using Mistral.</div><div class=""><br class=""></div><div class="">Thanks</div><div class=""><br class=""><div class="">
<div class="">Renat Akhmerov</div><div class="">@ Mirantis Inc.</div><div class=""><br class=""></div><br class="Apple-interchange-newline">
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<br class=""><div class=""><blockquote type="cite" class=""><div class="">On 17 Feb 2015, at 03:06, Dmitri Zimine <<a href="mailto:dzimine@stackstorm.com" class="">dzimine@stackstorm.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="Content-Type" content="text/html charset=windows-1252" class=""><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div class="">SUMMARY: </div><div class="">----------------</div><div class=""><br class=""></div>We are changing the syntax for inlining YAQL expressions in Mistral YAML from {1+$.my.var} (or “{1+$.my.var}”) to <% 1+$.my.var %><div class=""><br class=""></div><div class="">Below I explain the rationale and the criteria for the choice. Comments and suggestions welcome.</div><div class=""><div class=""><br class=""></div><div class="">DETAILS: </div><div class="">-------------</div><div class=""><br class=""></div><div class="">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:</div><div class=""><br class=""></div><div class=""><div class=""> publish:<br class=""> intvalue1: "{1+1}” # Confusing: you expect quotes to be string.<br class=""> intvalue2: "{int(1+1)}” # Even this doestn’ clean the confusion<br class=""> whatisthis:"{$.x + $.y}” # What type would this return? </div></div><div class=""><br class=""></div><div class="">We got a very strong push back from users in the filed on this syntax. </div><div class=""><br class=""></div><div class="">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.</div><div class=""><br class=""></div><div class=""><div class="">Criteria for selecting best alternative are: </div><div class="">1) Consistently applies to to all cases of using YAML in DSL</div><div class="">2) Complies with YAML </div><div class="">3) Familiar to target user audience - openstack and devops</div></div><div class=""><br class=""></div><div class="">We prefer using two-char delimiters to avoid requiring extra escaping within the expressions.</div><div class=""><br class=""></div><div class=""><div class="">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]):</div></div><div class=""><br class=""></div><div class=""><div class="">ALTERNATIVES considered:</div><div class="">--------------------------------------------------</div><div class=""><br class=""></div><div class="">1) Use Ansible-like syntax: <a href="http://docs.ansible.com/YAMLSyntax.html#gotchas" class="">http://docs.ansible.com/YAMLSyntax.html#gotchas</a></div><div class="">Rejected for confusion around types. See above.</div><div class=""><br class=""></div><div class="">2) Use functions, like Heat HOT or TOSCA:</div><div class=""><br class=""></div><div class="">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:</div><div class=""><br class=""></div><div class=""> publish:</div><div class=""> - bool_var: { yaql: “1+1+$.my.var < 100” } </div><div class=""><br class=""></div><div class="">Not bad, but currently rejected as it reads worse than delimiter-based syntax, especially in simplified one-line action invocation.</div><div class=""><br class=""></div><div class="">3) < > paired with other symbols: php-styoe <? ..?></div><div class=""><br class=""></div></div><div class=""><br class=""></div><div class=""><b class="">REFERENCES: </b></div><div class="">----------------------</div><div class=""><br class=""></div><div class="">[1] Allow arbitrary YAQL expressions, not just ones started with $ : <a href="https://github.com/stackforge/mistral/commit/5c10fb4b773cd60d81ed93aec33345c0bf8f58fd" class="">https://github.com/stackforge/mistral/commit/5c10fb4b773cd60d81ed93aec33345c0bf8f58fd</a></div><div class="">[2] Use Ansible-like syntax to make YAQL expressions YAML complient <a href="https://github.com/stackforge/mistral/commit/d9517333b1fc9697d4847df33d3b774f881a111b" class="">https://github.com/stackforge/mistral/commit/d9517333b1fc9697d4847df33d3b774f881a111b</a></div><div class="">[3] Preserving types in YAQL <a href="https://github.com/stackforge/mistral/blob/d9517333b1fc9697d4847df33d3b774f881a111b/mistral/tests/unit/test_expressions.py#L152-L184" class="">https://github.com/stackforge/mistral/blob/d9517333b1fc9697d4847df33d3b774f881a111b/mistral/tests/unit/test_expressions.py#L152-L184</a></div><div class="">[4]Using <% %> in Puppet <a href="https://docs.puppetlabs.com/guides/templating.html#erb-is-plain-text-with-embedded-ruby" style="font-family: 'Helvetica Neue'; font-size: 13px;" class="">https://docs.puppetlabs.com/guides/templating.html#erb-is-plain-text-with-embedded-ruby</a> </div><div class="">[5] Etherpad with discussion <a href="https://etherpad.openstack.org/p/mistral-YAQL-delimiters" class="">https://etherpad.openstack.org/p/mistral-YAQL-delimiters</a></div><div class=""><div class="">[6] Blueprint <a href="https://blueprints.launchpad.net/mistral/+spec/yaql-delimiters" class="">https://blueprints.launchpad.net/mistral/+spec/yaql-delimiters</a></div></div></div><div class=""><br class=""></div></div></div></blockquote></div><br class=""></div></div></div></blockquote></div><br class=""></div></body></html>