F# Money Types

money.fs

open System

// Define units of measurement
[<Measure>] type USD
[<Measure>] type BTC
[<Measure>] type percent

let btcUsdRate = 62500m<USD/BTC>

// Money type alias
type Money<[<Measure>] 'currency> = decimal<'currency>
type Percentage = decimal<percent>

// Money module
module Money =
    let increaseBy<[<Measure>] 'currency> (p: Percentage) (m: Money<'currency>) : Money<'currency> =
        m * (1m + decimal p / 100m)

    let decreaseBy<[<Measure>] 'currency> (p: Percentage) (m: Money<'currency>) : Money<'currency> =
        m * (1m - decimal p / 100m)

    let allocate<[<Measure>] 'currency> (m: Money<'currency>) (count: int) : Money<'currency> list =
        let baseAllocation = m / decimal count
        let remainder = decimal m % decimal count

        [1..count]
        |> List.map (fun i -> 
            if i <= int remainder 
            then baseAllocation + LanguagePrimitives.DecimalWithMeasure<'currency> 1m
            else baseAllocation)

    let allocateByRatios<[<Measure>] 'currency> (m: Money<'currency>) (ratios: Percentage list) : Money<'currency> list =
        let totalRatio = ratios |> List.sumBy (fun r -> decimal r / 100m)
        if Math.Abs(1m - totalRatio) > 0.0001m then
            failwith "Sum of ratios must be 100%"

        let allocations = 
            ratios
            |> List.map (fun r -> m * (decimal r / 100m))

        let totalAllocated = allocations |> List.sum
        let remainder = m - totalAllocated

        allocations
        |> List.mapi (fun i a -> 
            if i = 0 then a + remainder else a)

// USD examples
let usdPrice = 100m<USD> 
let usdShipping = 5m<USD>
let usdSubtotal = usdPrice + usdShipping
let discount = 10m<percent>
let usdTotal = Money.decreaseBy discount usdSubtotal

let ratios = [60m<percent>; 40m<percent>]

let usdEqualAllocation = Money.allocate usdTotal 2
let usdRatioAllocation = Money.allocateByRatios usdTotal ratios

// Print USD results
printfn "USD Price: %A" usdPrice
printfn "USD Shipping: %A" usdShipping
printfn "USD Subtotal: %A" usdSubtotal
printfn "Discount: %A%%" discount
printfn "USD Total: %A" usdTotal
printfn "USD Equal allocation: %A" usdEqualAllocation
printfn "USD Ratio allocation: %A" usdRatioAllocation

// BTC examples
let btcPrice = 0.01607580m<BTC>
let transactionFee = 1.25m<percent>
let btcTotal = Money.increaseBy transactionFee btcPrice
let btcInstallments = Money.allocate btcTotal 3

// Print BTC results
printfn "\nBTC Price: %A" btcPrice
printfn "BTC Total with fee: %A" btcTotal
printfn "BTC Installments: %A" btcInstallments

// Demonstration of type safety
let invalidAdd = usdPrice + btcPrice  // This will cause a compile-time error
let exchangedUsd = btcPrice * btcUsdRate  // This is valid
let validBtcAllocate = Money.allocate btcTotal 2  // This is valid and works with BTC