How do you define money type in F#

Question

Can you suggest a best way to define money type in F#?

Answer 1

use a long, and store pennies (or tenths of a penny) in it.

You could use a class like Decimal, but that usually ends up being quite slow.

Answer 2

Always, always, use System.Decimal for storing financial data! (Unless you dont care about inaccuracy and rounding errors!) http://msdn.microsoft.com/en-us/library/364x0z75(VS.71).aspx

Answer 3

type money = int<dollars>?

Haven't even tried it to see... can you define arbitrary units, or does it only work with explicitly defined ones?

Obviously you'd probably want

type money = int<thousandths_of_currency> (or tens of pennies, or whatever).

To be more accurate.

edited:

decimals take types so you can define money as:

[<Measure>]

type = pounds

type money = decimal<pounds>

which could ensure currencies aren't cross converted by accident, eg:

if

balance = decimal<pounds>

and

payment = decimal<dollars>

newbalance = balance + payment

will not compile, and you'll have to convert payment to decimal<pounds>

Answer 4

Luca Bolognese suggests one defines their own Money type based off of float:

[<Measure>] type money
let money (f:float) = f * 1.<money>

Answer 5

F# now has built in support for Measures and Units. According to the lead engineer for this feature, Kennedy it is aimed at financial apps among other solutions.

So I would look at that before defining my own money type in F#.

Werner