Fhir mapping language examples

My team is interested in implementing the fhir mapping language, but we can’t find clear examples of language semantics. I also can’t get the java validate_cli.jar to work; it keeps throwing exceptions.

To implement the language, we need to be able to execute simple maps with a reference implementation to validate our assumptions.

For example, I expect this map

map "http://hl7.org/fhir/StructureMap/test" = test
group main(source src, target tgt) {
  src.ls as sls -> tgt.ls as tls;

applied to this input

    ls: [1, 2, 3],

To output

ls: [{}, {}, {}]

But I have no way of validating this. Could anyone shed light on this, or kindly point me in the right direction? Thanks!