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Dependencies, Fragments, and Callbacks

Dependencies​

> requires: Request Name

Dependencies create a DAG so setup requests run before dependents. Dependency captures require the referenced request to be declared in > requires: so the planner can guarantee the upstream result exists.

Use dependencies when later requests need values or ordering guarantees from earlier requests.

Fragments​

<< ./fragments/common_schema_types.hen
[ FEATURE_ENABLED == true ] << ./fragments/extra_assertions.hen
  • << path.hen imports another Hen file before parsing
  • fragment paths resolve relative to the importing file
  • guards can skip a fragment import entirely
  • fragments can contribute reusable declarations or request-local snippets

Callbacks​

! callback code
! ./path/to/callback_file.sh
! some command -> $VARIABLE_NAME
  • callback assignments require whitespace around ->
  • assignment form suppresses stdout and exports the captured value
  • callbacks run after request execution

Callbacks are a good fit for side effects such as notifications, local file writes, or shell-based post-processing that should happen after a request completes.

Combined Pattern​

<< ./fragments/export_shapes.hen

---

Create export

POST {{ API_ORIGIN }}/exports

~~~json
{"format":"csv"}
~~~

^ & status == 202
& body.id -> $EXPORT_ID

---

Wait for export

> requires: Create export
GET {{ API_ORIGIN }}/exports/{{ EXPORT_ID }}

^ & status == 200
^ & body === ExportStatus

! ./scripts/notify_export_ready.sh

In that flow, the fragment can contribute shared variables or schema targets such as API_ORIGIN and ExportStatus, the first request captures $EXPORT_ID, the second request uses that capture through an explicit dependency, and the callback script runs after the dependent request completes.

Dependencies, fragments, and callbacks work well together when you want:

  • a reusable shared preamble
  • a setup request that exports values
  • a later request that consumes those values
  • a callback that ships the result elsewhere after the request completes