FPML lacks range iteration

[kozlovana]

Need to add numeric/range iteration support in FPML (similar to JUTE’s $ range()):

While translating a working JUTE mapping medication-batch-create-extract to FPML, a hard blocker was encountered:
FPML’s {% for %} requires an array to iterate over, while this mapping needs to iterate N times based on an integer input (items-number).

The JUTE mapping medication-batch-create-extract uses $map: $ range(0, itemsNumber, 1) to create multiple Medication resources.
FPML currently has no equivalent — {% for %} only works with arrays, not integers.
As a result, this mapping cannot be translated to FPML.

[ruscoder]

I though about different syntaxes:

1. Liquid style {% for i in (0..1) %} - it conflict with fhirpath expression that also might be wrapped into parentheses.
2. Magic collection {% for i in %n %} - same construction, but magic implicit behaviour with number as collection. Error-prone
3. New keyword instead of in {% for i times %n %} - hard to read, not common
4. New construction {% repeat %n %} and {% repeat %n as index %} - I really like it, but it introduces new construction. But it's explicit and handles this specific case.
5. Fhirpath custom function/factory {% for i in range(5) %} or {% for i in %factory.range(5) %} - clean solution, requires custom function/factory. But out of spec for now

@ir4y what do you think?