State Machine

A state machine defines a global state and transitions from one state to another.

Archetype provides the possibility to design the contract as a state machine; it simplifies the management of the contract's state compared to a manual management with bool or nat variables, because the only way to change the contract state is through transition entrypoints, which puts the contract's state under explicit control.

States

The states keyword is used to declare the contract's states.

For example:

states =
| Pending initial
| Shipped
| Accepted
| Rejected
| Canceled

See the states article for more information.

Transitions

A transition is an entrypoint that changes the contract states. It provides a dedicated syntax to define guard conditions and transition effect.

For example, the following entrypoint

transition accept() {
  called by buyer
  from Shipped
  to   Accepted
  with effect {
    transfer balance to seller
  }
}

See the transition article for more information.

Check state

Section

The state is section allows the execution of an entrypoint (ie does not fail) only when the contract is in the specified state.

For example, the following entrypoint fails if the current contract state is not Accepted:

entry pay() {
  state is Accepted
  /* ... other sections ... */
}

See the Sections article for more information on sections.

state constant

It is possible to interrogate the contract state anywhere in any entrypoint effect with the state constant. It is not possible to assign a value with an assignment instruction. Use a transition to change contract's state.

The constant may be interrogated with an if or a match with instruction.

For example:

if state = Canceled then /* ... */

or:

match state with
| Pending  -> instr1 /* when in Pending  state */
| Shipped  -> instr2 /* when in Shipped  state */
| Accepted -> instr3 /* when in Accepted state */
| Rejected -> instr4 /* when in Rejected state */
| Canceled -> instr5 /* when in Canceled state */
end;