How to use Validation applicative from F#

Discussions.1293.fs

module Validation =
    open LanguageExt

    let successValue (ma : Validation<'f, 'a>) : 'a =
        ma.IfFail(fun () -> failwith "Validation monad is in a Fail state")
        
    let apply (mf : Validation<'f, 'a -> 'b>) (ma : Validation<'f, 'a>) : Validation<'f, 'b> =
        mf.Disjunction(ma)
          .Map(fun _ -> (successValue mf) (successValue ma))
    
    let map (f : 'a -> 'b) (ma : Validation<'f, 'a>) : Validation<'f, 'b> =
        ma.Map(f)
    
    let success x : Validation<'f, 'a> =
        Validation<'f, 'a>.Success(x)
    
    let fail x : Validation<'f, 'a> =
        Validation<'f, 'a>.Fail(Prelude.Seq1(x))
    
    let (<*>) = apply
    let ($) = map

    let add = fun x y -> x + y
    let mf = success add
    let ma = success 123
    let mb = success 456
    
    let mr = mf <*> ma <*> mb
    let mr2 = add $ ma <*> mb