Control Flow

if: — conditional execution

Two forms. A single-step condition, or a multi-step branch with do: and an optional else:.

using:
  - zenvara/email
  - zenvara/noop

output:
  ok: !bool

steps:
  # Single-step condition
  - if: count > 0
    $notify:
      invoke: email.send
      with: { From: "alerts@example.com", To: "${alert}", Subject: "Data arrived", Body: "New data has arrived." }

  # Multi-step branch
  - if: "len(items) > 0"
    do:
      - log: "Processing ${= len(items)} items"
      - $result:
          transform: noop.invoke
          with: { Value: "${items}" }
    else:
      - log: "Nothing to process"

  - return:
      ok: true

Conditions are plain expressions — no ${= ... } wrapper. if: count > 0 is correct; if: "${= count > 0}" is not.

for-each: — iteration

Iterate a list or a map. Inner steps are sandboxed by default — they cannot modify the outer payload. Name the loop to collect outputs.

using:
  - zenvara/noop

output:
  batched: !obj-list

steps:
  # Side-effect-only loop (sandboxed)
  - for-each: $item in "${products.rows}"
    do:
      - log: "Row ${_index} of ${_count}: ${item.name}"

  # Named loop — collects each iteration's output
  - $batched:
      for-each: $item in "${products.rows}"
      collect:
        _value: "${row.Value}"
      do:
        - $row:
            transform: noop.invoke
            with: { Value: "${item}" }

  - return:
      batched: "${batched.items}"

Loop variables available inside do::

Variable	Meaning
$item (or your chosen name)	The current element.
_index	1-based position.
_count	Total number of elements.
_key	The current key (map iteration only).

switch: — multi-branch matching

Two modes: match a value against named cases, or evaluate boolean expressions in order (first match wins).

using:
  - environment/prod
  - zenvara/http

output:
  ok: !bool

steps:
  # Value mode
  - switch:
      on: "${order.status}"
      case:
        paid:
          - $ship:
              invoke: http.post
              on: warehouse
              with: { Hosts: ["https://warehouse.example.com"], Url: "/shipments", Body: { orderId: "${order.id}" } }
        cancelled:
          - log: "Skipping cancelled order ${order.id}"
        default:
          - log: "Unhandled status: ${order.status}"

  # Expression mode (first match wins)
  - switch:
      cases:
        "len(items) > 1000":
          - log: "Large batch — escalating"
        "len(items) > 0":
          - log: "Small batch"
        default:
          - log: "Empty batch"

  - return:
      ok: true

stop: / skip: — stopping execution

- stop: "no records to process"       # terminates the entire flow — reason is mandatory

- for-each: $row in "${products.rows}"
  do:
    - if: row.qty <= 0
      skip: "out-of-stock row"        # ends this iteration; loop continues
    - log: "Processing ${row.id}"

Use stop: "<reason>" to end the entire run without producing output (contrast with return:, which produces the typed output and ends). Use skip: "<reason>" inside a for-each:/stream: to move on to the next item — outside a loop it is a validation error. A bare stop: never runs compensation; pair it with the mapping form stop: { reason: "...", compensate: true } to roll back prior steps in a transactional flow.