Library $evaluate unable to handle returned sets

[Capt-Mac]

Problem:

When running Library $evaluate for specific expression return types it appears that the operation is unable to render the results into a FHIR parameter component.

This is a problem because the operation is fully unusable without these types of scenarios.

example CQL:

define "Related Encounters":
  from
   [Encounter] Encounter,
    [Condition] Pregnancy
        where AC.ActiveDiagnosisPeriod(Encounter, Condition) overlaps Encounter.period
            and AgeInYearsAt(start of Encounter.period) between 14 and 50
    return { condition: Condition, ed: Encounter }

Error returned when evaluating CQL with this type of expression within it:

{
    "resourceType": "Parameters",
    "parameter": [
        {
            "name": "evaluation error",
            "resource": {
                "resourceType": "OperationOutcome",
                "issue": [
                    {
                        "severity": "error",
                        "code": "exception",
                        "diagnostics": "unknown type when trying to convert to parameters: ParametersParameterComponent"
                    }
                ]
            }
        }
    ]
}

Scope:

Allow the output of sets of resources like the example above to populate in a parameter component. Choose a format that would indicate the expression the result is sourced from and the alias related to the displayed result

[JPercival]

CQL is able to represent a broader of set of types than FHIR (since CQL is not FHIR-specific). The Using CQL with FHIR IG specifies the set of types that can be used in FHIR-based CQL (and, transitively, with operations such as $evaluate):

https://build.fhir.org/ig/HL7/cql-ig/conformance.html#conformance-requirement-4-3

Essentially, even though you can write the CQL above it's not valid for FHIR use-cases.

IOW, this is something to take up as standards feedback.