A Groovy way to demonstrate banking a fiat currency.

gistfile1.groovy

class Goldsmith {

    def unitsOfGold = 0
    def depositReceipts = 0
    def loanReceipts = 0
    def reserveFraction = 0

    def deposit(goldDeposit) {
        unitsOfGold += goldDeposit
        depositReceipts += goldDeposit
        println "Units of Gold: " + unitsOfGold
        println "Deposit Receipts: " + depositReceipts
        calculateBacking()        
    }

    def issueLoans(int perCentDeposits) {
        println "Issuing loans at percent of deposits: " + perCentDeposits
        loanReceipts += (perCentDeposits/100)*unitsOfGold
        println unitsOfGold + " units of gold for " + (depositReceipts+loanReceipts) + " receipts"
        calculateBacking()
    }

    def calculateBacking() {
        reserveFraction = unitsOfGold / (depositReceipts+loanReceipts) * 100
        def roundedBacking = Math.round(reserveFraction)
        println "Backing: " + roundedBacking + "%"
        if (roundedBacking == 0) println "Pure FIAT money!!"
    }
}

def goldsmith = new Goldsmith()

goldsmith.deposit(100)
goldsmith.deposit(100)
goldsmith.deposit(100)
goldsmith.deposit(100)
goldsmith.deposit(100)

goldsmith.issueLoans(900)