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 = @tz1Lc2qBKEWCBeDU8npG6zCeCqpmaegRi6Jg
constant patient : role = @tz1bfVgcJC4ukaQSHUe1EbrUd5SekXeP9CWk
​
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 confirm () {
  from Created
  (*signed by [insrurer; patient]*)
  to Running
  with effect {
    last_fee := now
  }
}
​
transition cancel () {
  called by insurer or patient
  from Created
  to Canceled
}
​
entry register_doctor (docid : address) {
  (*signed by [insurer; patient]*)
  require {
     r1 : state = Running;
  }
  effect {
    doctor.add ({ id = docid })
  }
}
​
entry declare_consultation (v : tez) {
  require {
     r2 : state = Running;
     r3 : doctor.contains(caller);
  }
  effect {
    doctor.update(caller, { debt += v });
    consultation_debt += min (v, deductible)
  }
}
​
entry 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[docid].debt;
    var decrease : tez = min (transferred, ldebt);
    transfer decrease to docid;
    transfer (transferred - decrease) to insurer;
    doctor.update (docid, { debt -= decrease })
  }
}
​
entry pay_fee () {
  specification {
    postcondition idem_balance_pay_fee {
      balance = before.balance
    }
  }
  accept transfer
  called by patient
  require {
    r5 : state = Running;
  }
  effect {
    var nb_periods : int = (now - last_fee) div period;  (* div is euclidean *)
    var due = nb_periods * fee;
    var decrease : tez = min (transferred, due);
    transfer decrease to insurer;
    transfer (transferred - decrease) to patient;
    last_fee += nb_periods * period     (* last_fee <> now because div is euclidean *)
  }
}
​
entry pay_consulation () {
  specification {
    idem_balance_pay_consultation : balance = before.balance;
  }
  accept transfer
  called by patient
  require {
    r6 : state = Running;
  }
  effect {
    var decrease : tez = min (transferred, consultation_debt);
    transfer decrease to insurer;
    transfer (transferred - decrease) to patient;
    consultation_debt -= decrease
  }
}
​
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