CODEWITHSUNDEEP
f#
Sal-laS
Sal-laS

Reputation: 11649

This value is not a function and cannot be applied

Pretty simple function for operation of negation.

let negation (value:option<bool>) =
   match value with
   |Some true -> Some false
   |Some false -> Some true
   |None -> failwith "OOPS"

but when i call it:

negation Some true

it complains that 

This value is not a function and cannot be applied

Upvotes: 2

Views: 6015

Answers (1)

Bartek Kobyłecki
Bartek Kobyłecki

Reputation: 2395

You need some parens there:

negation (Some true)

Or:

negation <| Some true

Without the parens like that F# compiler would understand that line as

(negation Some) true

because function application is left-binding and then types are not match: negation would need to be of type: ('a -> option 'a) -> bool -> bool which clearly isn't (is of type bool option -> bool option)

In addition: (opinion included)

Negation function is called not : bool -> bool. You are trying to use that on the bool wrapped by option, so maybe that should be sufficient:

let negation : bool option -> bool option = Option.map not

Upvotes: 10

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