Health care

Health insurance example
This contract is adapted from the DAML 's  introductory insurance contract.
DAML is a distributed private ledger and does not manage payments; the contract allows the doctor to generate bills for insurer and patient. 
The strength of a public blockchain with a cryptocurrency, is that it allows payments and accounting of payments in a single business process. The main differences between the contract below and the DAML version are:
payments are executed through contract entries
the contract enters the Running state with validation from both insurer and patient parties
The main benefit of this version is that it may serve as an opposable document in the case of a default in payment: indeed, since the contract is used to channel payments, the contract is accounting for any default of payment (in the debts variables).
For example, a doctor may go to court and exhibit the debt value of his corresponding doctor asset as a proof of the default in payment.
From a design point of vue, the contract manages several doctors. A doctor is registered with approvals from both patient and insurer parties.
We see in this basic example, that a smart contract on a public blockchain with a cryptocurrency, enables organisations to capture the critical aspects of a business process : payments, permissions and accounting.
archetype health_care
​
constant insurer : role = @tz1KksC8RvjUWAbXYJuNrUbontHGor25Cztk
constant patient : role = @tz1KksC8RvjUWAbXYJuNrUbontHGor25Cztk
​
constant fee : tez = 100tz
constant deductible : tez = 500tz
constant period : duration = 30d
​
variable last_fee : date = 2019-11-12
​
variable consultation_debt : tez = 0tz
​
asset doctor identified by id {
  id   : role;
  debt : tez = 0tz;
}
​
states =
| Created   initial
| Running
| Canceled
​
transition[%signedbyall [patient; insurer]%] confirm () from Created {
  (*signed by [insrurer; patient]*)
  to Running
  with effect {
    last_fee := now
  }
}
​
transition cancel () from Created {
  called by insurer or patient
  to Canceled
}
​
action[%signedbyall [patient; insurer]%] register_doctor (docid : address) {
  (*signed by [insurer; patient]*)
  require {
     r1 : state = Running;
  }
  effect {
    doctor.add ({ id = docid })
  }
}
​
action declare_consultation (v : tez) {
  require {
     r2 : state = Running;
     r3 : doctor.contains(caller);
  }
  effect {
    doctor.update(caller, { debt += v });
    consultation_debt += min (v, deductible)
  }
}
​
action pay_doctor (docid : address) {
  specification {
    postcondition idem_balance_pay_doctor {
      balance = before.balance
    }
  }
  accept transfer
  called by insurer
  require {
    r4 : state = Running;
  }
  effect {
    var ldebt = doctor.get(docid).debt;
    var decrease : tez = min (transferred, ldebt);
    transfer decrease to docid;
    transfer (transferred - decrease) to insurer;
    doctor.update (docid, { debt -= decrease })
  }
}
​
action pay_fee () {
  specification {
    postcondition idem_balance_pay_fee {
      balance = before.balance
    }
  }
  accept transfer
  called by patient
  require {
    r5 : state = Running;
  }
  effect {
    let nb_periods : int = (now - last_fee) / period in  (* div is euclidean *)
    let due = nb_periods * fee in
    let decrease : tez = min (transferred, due) in
    transfer decrease to insurer;
    transfer (transferred - decrease) to patient;
    last_fee += period * nb_periods     (* last_fee <> now because div is euclidean *)
  }
}
​
action pay_consulation () {
  specification {
    idem_balance_pay_consultation : balance = before.balance;
  }
  accept transfer
  called by patient
  require {
    r6 : state = Running;
  }
  effect {
    let decrease : tez = min (transferred, consultation_debt) in
    transfer decrease to insurer;
    transfer (transferred - decrease) to patient;
    consultation_debt -= decrease
  }
}
​
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