'option<unit->unit> type and the equality' using F#

Consider th开发者_开发技巧e following code:

let fnOption = Some (fun () -> ())
fnOption = None

It gives the following error:

init.fsx(2,1): error FS0001: The type '(unit -> unit)' does not support the 'equality' constraint because it is a function type

Why is that? Did I overlook something?

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If you really wanted to check for equality (and not to assign the value), then you can use Option.isNone fnOption. If you really do want to assign, look as kvb's answer.

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It's unclear what you're trying to do. As it stands, the second line is an equality test, not an assignment. If what you intended to do was assign a new value to fnOption, then you need to make it mutable:

let mutable fnOption = Some(fun () -> ())
fnOption <- None

If you are really trying to test equality, then the error you are seeing is the expected result, because functions aren't comparable.