Custom exceptions in F#

We can build custom exceptions in F# with the exception keyword. We can also assign multiple parameters to it in a tuple:

exception ProductNotFoundException of string * int * int

We can raise a custom exception with the raise function. The with clause will have a pattern matching section where we can decide what to do with the various exception types:

let customExceptionRaise =
    try
        raise (ProductNotFoundException("Book", 10, 543665))
    with
        | ProductNotFoundException(productName, quantity, id) ->
            printfn "We don't have %d pieces of product name %s id %d" quantity productName id

Executing this function will produce the following output:

We don’t have 10 pieces of product name Book id 543665

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