Loop: repeat, while, break, and continue

Goal

Use the other two loop modes and leave a loop early. Time: 15 minutes.

repeat: a fixed count

- id: poll
  kind: loop
  repeat: 3
  body:
    - id: ping
      kind: http
      url: "mock://status/{{ loop.index }}"

while: repeat while a condition holds

The condition is checked before each pass. The body must change the value it tests, otherwise the loop only stops at max.

schema: 1
name: Countdown
id: countdown
blocks:
  - id: start
    kind: code
    language: python
    body: |
      import json; print(json.dumps({"more": True}))
    outputs:
      type: object
      properties:
        more: { type: boolean }
  - id: drain
    kind: loop
    while: steps.start.more == true
    max: 5
    body:
      - id: work
        kind: code
        language: python
        uses: [loop.index]
        body: |
          import json, os
          i = json.load(open(os.environ["TERMORQ_INPUT"], encoding="utf-8"))["loop"]["index"]
          print(json.dumps({"done_at": i}))
        outputs:
          type: object
          properties:
            done_at: { type: number }
        then: break

repeat and while loops don’t have loop.item, so leave it out of uses.

break and continue

Inside a loop body, then accepts two special targets:

`then:`	Effect
`break`	Leave the loop. The run continues after the loop
`continue`	Skip the rest of this pass and start the next one

Outside a loop, the run fails: ‘break’ is only valid inside a loop.

A common pattern is a Decision inside the body whose branches end in then: continue or then: break:

body:
  - id: check
    kind: decision
    branches:
      - when: loop.item == "stop"
        goto: halt
      - else: true
        goto: process
  - id: halt
    kind: http
    url: mock://halt
    then: break
  - id: process
    kind: http
    url: "mock://item/{{ loop.index }}"
    then: continue

Check your run

Countdown runs work once (done_at: 1), then leaves the loop because of then: break. Without break, it would stop at max: 5, because steps.start.more never changes.

Exercise

Set max: 101 on any loop, then save and run it. What happens? Then try a loop of 60 nested inside another loop of 2.

Details

Save accepts it (it’s a number), but the run fails with The loop maximum is 101, and the ceiling is 100. The nested 2 × 60 = 120 passes goes over the 100-passes-per-run limit, so the run fails with This run reached 100 passes. or The loop would run … passes, and this run allows 100.