Control Flow

if: — conditional execution

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

# Single-step condition
- if: count > 0
  $notify:
    invoke: email.send
    with: { To: "${alert}", Subject: "Data arrived" }

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

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.

# 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}"
    do:
      - $row:
          invoke: transform.run
          with: { Data: "${item}" }

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).

# Value mode
- switch:
    on: "${order.status}"
    case:
      paid:
        - $ship:
            invoke: warehouse.create-shipment
      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"

halt: — stopping execution

- halt: true                 # exit the current loop
- halt: { global: true }     # terminate the whole flow

Use halt: true to break out of a for-each:; use halt: { global: true } to stop the entire invocation without producing output (contrast with return:, which produces the typed output and ends).