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Comparing F # discriminated union instances using pattern matching

Firstly, apologies for the bad title - I don't understand F # enough to better describe the problem.

Consider this simple DU:

type Money =
    | USD of decimal
    | GBP of decimal
    | EUR of decimal
    static member (+) (first: Money, second: Money) =
        match first, second with 
        | USD(x), USD(y) -> USD(x + y)
        | GBP(x), GBP(y) -> GBP(x + y)
        | EUR(x), EUR(y) -> EUR(x + y)
        | _ -> failwith "Different currencies"

I represent money in different currencies and overloading the operator (+) so that I can safely make money + money. However, if I have a lot of currencies, then the statement of conformity will be tedious to write. Is there a way to express something like:

match first, second with 
| _(x), _(y) -> _(x + y)

Or is there another way to achieve the same result? I reviewed and discarded units due to the limitations described here .

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1 answer

Does this work for you?

type Kind = | USD | GBP | EUR

type Money = 
    | Money of Kind * decimal 
    static member (+) (first: Money, second: Money) = 
        match first, second with  
        | Money(k1,x), Money(k2,y) when k1=k2 -> Money(k1, x + y) 
        | _ -> failwith "Different currencies"
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