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Tutorial · Grade 111. Route the Payment

Process every transaction by picking the cheaper online provider.

Scenario

Two providers are available. Provider B offers lower fees than Provider A.

Problem statement

Welcome to YamusaPay's Payment Routing Switch!

Incoming transactions arrive in a queue. Both Provider A and Provider B are online, but Provider B charges a lower fee per transaction.

Your task is to create your very first routing rule: whenever Provider B is online, route transactions through Provider B to minimize fees!

The starter brain has no rules.

Since Provider B is cheaper and online, add a rule: WHEN onlineB -> DO route-b. This clears the payment queue at minimum cost.

What this teaches

Read provider facts and choose the lowest-cost route.

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.

No rules yet. Nothing will happen until you add at least one rule.