How to define F# generic function argument in a generic function?

Question

let getLogicalWithDoubleLevelElement<'E when 'E :> DoubleLevelElement>
    (logicalModifier : InletPosition * OutletPosition -> Logical)
    (logical : Logical) =

I need logicalModifier to be generic function with type the same type argument as getLogicalWithDoubleLevelElement .

How to define that?

Answer 1

If you need to pass an explicitly polymorphic function as an argument, then the only way to do that in F# is to use a new type with a generic method:

type LogicalModifier =
    abstract MakeLogical<'E when 'E :> DoubleLevelElement> : InletPosition * OutletPosition -> Logical

let getLogicalWithDoubleLevelElement<'E when 'E :> DoubleLevelElement>
    (logicalModifier : LogicalModifier)
    (logical : Logical) = ... logicalModifier.MakeLogical<'E> ...