←
Build the decisionSaved automatically
Tutorial · Grade 212. Mind the Offline Provider

Route payments to Provider B because Provider A is offline.

Scenario

Provider A has a cheaper fee listed, but it is currently offline. Provider B is online.

Problem statement

The starter rule attempts to route every transaction to Provider A because its fee is lower. However, Provider A is currently offline, so every attempt fails!

A low fee is useless if the provider is offline. Verify provider availability first: route transactions to Provider B while Provider B is online.

The provider status shows Provider A as offline. The naive rule `WHEN hasTransaction -> DO route-a` fails.

Change the rule to: WHEN onlineB -> DO route-b to bypass the offline provider cleanly.

What this teaches

Check availability constraints (onlineB) before evaluating price or fees.

Scroll down to build and test your solution.

Active controller

Apply & Run executes only the selected controller.

How a rule works

A rule has two parts:

WHEN <something is true> → DO <this action>

  • WHEN is a question about what is happening right now. For example: "Is it raining?" or "Is there a wall ahead?"
  • DO is what happens when the answer is yes.
  • The simulation runs one step at a time.
  • On each step, the rules are checked from top to bottom.
  • The first rule that is true wins. The rules below it are skipped for that step.
  • To change which rule wins, move it up or down the list.
  • If no rule is true, nothing happens on that step.
  • Some actions have more than one step, like "turn right, then move". You build these in the Functions tab.
  • Once a multi-step action starts, it finishes all its steps before the rules are checked again. It only stops early if the next step is not safe.
See an example

Two rules for deciding about an umbrella:

1  WHEN isRaining  → take an umbrella
2  WHEN always     → leave the umbrella at home
  • It is raining. Rule 1 is true, so you take an umbrella. Rule 2 is skipped.
  • It is sunny. Rule 1 is false, so rule 2 is checked next. Rule 2 is always true, so you leave the umbrella at home.
  • Order matters. If rule 2 were on top, it would be true every day, and you would never take an umbrella.

Rule folders

Categorise cards without changing their global execution order.

⋮⋮1
Folder
WHEN
DO