State machine

It is possible to design the smart contract as a state machine which is convenient for ease of read.

In this exercise, the machine has 4 states and 3 transitions as illustrated in the shcema below:

Transitions have conditions:

• goes in InProgress state if balance is greater than 3tz
• complete if internal value is strictly greater than 1 (requires calls to inc_value)

6-state_machine.arl

archetype state_machine

states =
| Created initial
| InProgress
| Interrupted
| Completed

variable value : nat = 0

entry inc_value () {
  value += 1
}

transition init () {
  from Created to InProgress
  when { transferred > 3tz }
  with effect { () /* nothing */}
}

transition complete () {
  from InProgress to Completed
  when { value > 1 }
  with effect { transfer balance to caller }
}

transition interrupt () {
  from InProgress to Interrupted
  with effect { transfer (50% * balance) to caller }
}

Each transition is a contract entry point.

Deploy

The following Completium CLI command deploys the contract on the Tezos network:

completium-cli deploy 6-state_machine.arl

Call entry points

In this example it is necessary to call specific entry points. A contract's entrypoints may be listed with:

completium-cli show entries 6-state_machine

The goal here is to set the state machine to Completed state. Use the following commands to transit the machine:

completium-cli call 6-state_machine --entry init --amount 5tz

completium-cli call 6-state_machine --entry inc_value

completium-cli call 6-state_machine --entry inc_value

At this stage, value is 2, which allows transiting to Completed.

completium-cli call 6-state_machine --entry complete

This last call may be replaced by the following command to go to Interrupted state:

completium-cli call 6-state_machine --entry interrupt

Next

Open '7-assets.arl' and click on "Next: Assets" below.