Pattern builder interface similar to ExtensionGenerator.xtend

Although we don't consider it as a public API at the moment, it would be nice to have a concise way of creating patterns from code. I think this could work similarly to the ExtensionGenerator used by the generator fragments.

Syntax ideas:

val pattern = patternBuilder.pattern("myRuntimePackage.myRuntimePattern")[
  patternBuilder.parameter("MyParam", EcorePackage::eInstance.EClass)
  patternBuilder.eClassifierConstraint("MyVar", EcorePackage::eInstance.EReference)
  patternBuilder.pathExpression("MyParam", "MyVar", EcorePackage::eInstance.EClass_EAttributes)
  patternBuilder.patternCall("someOtherPackage.otherPattern", "MyVar")
]
if(patternBuilder.validate(pattern)){
  val fact = MatcherFactoryRegistry::getOrCreateMatcherFactory(pattern)
  fact.getMatcher(resourceSet).forEachMatch[
    println(prettyPrintMatch())
  ] 
}

Of course, it allows for nice tricks like:

path expressions and pattern calls can have their last parameter as EStructuralFeature... and String... to enable longer paths and unnamed variables
allow internal pattern definitions: patternBuilder.negPatternCall([...])[ patternBuilder.pathExpression()...]

While it also brings up questions like:

is it possible to support check expressions? Maybe we can just point it to a method definition that returns a boolean value?

The above examples didn't cover equality checks, count find, and annotations (although the later is probably not needed).

viatra / EMF-IncQuery

Pattern builder interface similar to ExtensionGenerator.xtend #363