CodeSystem as first-class type

[JSRankins]

ValueSetRef and CodeSystemRef were added as first-class types in CQL 1.5. Refer to http://www.hl7.org/dstucomments/showdetail_comment.cfm?commentid=1908. Some issues are being fixed with CQL 1.5.2 and have been addressed in the 1.5.6 CQL-to-ELM Translator. Capability needs to be added to the execution engine to support this 1.5 feature. This is a request to add capability for CodeSystemRef. Issue 226 is about adding ValueSetRef capability.

[IrickNcqa]

Adding a note of support for this feature from NCQA.

[cmoesel]

The CQL CodeSystem type represents a reference to a code system, allowing that code system to be passed into CQL functions.

To demonstrate how this might work, consider the following example:

library MyLibrary version '0.0.2'
codesystem MyCS: 'http://example.org/cs/mycs'
code Foo: 'Foo' from "MyCS" display 'Foo'

define function FooInCS(cs CodeSystem):
  Foo in cs

define IsFooInMyCVS:
  FooInCS(MyCS)

Much like the case for ValueSet (#226), the ELM representation of a function that takes a CodeSystem argument would be invoked with a CodeSystemRef.