FHIRPath Lab API should group on each context element

[johngrimes]

There is an optional field in FHIRPath Lab called "Context Expression".

The way this works for other implementations is that the main expression is executed for each element returned by the context expression.

The Pathling FHIRPath Lab server doesn't currently work this way, it simply returns a single collection.

[piotrszul]

Example: Expression execute response with context and trace

Context: name
Expression: trace('trc').given.join(' ').combine(family).join(', ')

The JSON below shows only the entries relevant to the evaluation result. Each result part corresponds to one context element (name[0], name[1], name[2]), and includes both the evaluated string result and the trace output capturing the intermediate value at the trace() call site.

{
    "name": "result",
    "part": [
        {
            "name": "string",
            "valueString": "Peter James, Chalmers"
        },
        {
            "name": "trace",
            "valueString": "trc",
            "part": [
                {
                    "name": "HumanName",
                    "valueHumanName": {
                        "use": "official",
                        "family": "Chalmers",
                        "given": [
                            "Peter",
                            "James"
                        ]
                    }
                }
            ]
        }
    ],
    "valueString": "name[0]"
},
{
    "name": "result",
    "part": [
        {
            "name": "string",
            "valueString": "Jim"
        },
        {
            "name": "trace",
            "valueString": "trc",
            "part": [
                {
                    "name": "HumanName",
                    "valueHumanName": {
                        "use": "usual",
                        "given": [
                            "Jim"
                        ]
                    }
                }
            ]
        }
    ],
    "valueString": "name[1]"
},
{
    "name": "result",
    "part": [
        {
            "name": "string",
            "valueString": "Peter James, Windsor"
        },
        {
            "name": "trace",
            "valueString": "trc",
            "part": [
                {
                    "name": "HumanName",
                    "valueHumanName": {
                        "use": "maiden",
                        "family": "Windsor",
                        "given": [
                            "Peter",
                            "James"
                        ],
                        "period": {
                            "end": "2002"
                        }
                    }
                }
            ]
        }
    ],
    "valueString": "name[2]"
}