Elm Supports Aggregrate Path should this CQL engine support aggagregate path

[vfrank66]

This is more a discussion as opposed to an issue, but I see that there are no public discussions on github and there is a private google repo where this probably occurs.

I see in the model.go // TODO: b/347346351 - In ELM it's modeled as an AggregateExpression, but for now we model it as an

CQL aggregrate functions look like in the spec look like

Sum([1, 2, 3])

ELM aggregate expressions support

Sum(Patient.observations.value)

Is this something desirable to support?

If yes this was my rough idea on howto add support

type IAggregateExpression interface {
    IExpression
    GetSource() IExpression
    GetPath() string
    IsDistinct() bool
    // To differentiate IAggregateExpression from other interfaces
    isAggregateExpression()
}

type AggregateExpression struct {
    *Expression
    Source   IExpression
    Path     string // Optional path to apply to each element
    Distinct bool   // Whether to apply distinct to the source before aggregation
}

func (a *AggregateExpression) GetSource() IExpression { return a.Source }
func (a *AggregateExpression) GetPath() string { return a.Path }
func (a *AggregateExpression) IsDistinct() bool { return a.Distinct }
func (a *AggregateExpression) isAggregateExpression() {}