let map oneTrackFunction twoTrackInput = match twoTrackInput with | Success s -> Success (oneTrackFunction s) | Failure f -> Failure f And here it is in use with canonicalizeEmail: let usecase = validate1 >=> validate2 >=> validate3 >> map canonicalizeEmail // normal composition Note that normal composition is now used because map canonicalizeEmail is a fully two-track function and can be connected to the output of the validate3 switch directly. In other words, for one-track functions, >=> switch is exactly the same as >> map. Your choice.
QUESTION
map can be defined using bind and switch,
let map f = bind (switch f)
but how to do this with >=>?...
ANSWER
Found a solution, but this is quite stupid:
let map' f result =
match result with
// The value of `o` is irrelevant, it is only needed
// because `>=>` returns a function, but we need
// a value and both operands of the input `f` are
// provided by the closures
| Ok o -> ((fun _ -> result) >=> (switch f)) o
| Error e -> Error e
NOTE<br /> Call them as:
map ((+) 2) ((Ok 27) : Result<int,string>);; map' ((+) 2) ((Ok 27) : Result<int,string>);;