Monad with safe division - idea from http://visualizationtools.net/default/categories-for-dummies/

gistfile1.fs

// 1. Define the monad 
type 'a Result = 
| Value of 'a
| Infinite

let bindF r (f: 'a -> 'a Result) =
    match r with
    | Value x -> f x
    | Infinite -> Infinite

let resultF = id

// 2. Use a computation expression builder
//     in order to allow syntactic sugar
type SafeOperationBuilder() =
    member this.Bind (r, f) = bindF r f
    member this.Return x = resultF x

// 3. Instanciate the monad
let safe = SafeOperationBuilder()

// 4. Define a safe division
let divide x y =
    match y with
    | 0.0 -> Infinite
    | _   -> Value(x/y)

// 5. Use the safe division in a computation expression
let totalResistance r1 r2 r3 =
    safe {
        // no DivideByZero exception occurs here
        let! x = divide 1.0 r1
        let! y = divide 1.0 r2
        let! z = divide 1.0 r3
        return divide 1.0 (x + y + z) 
    }

let result = totalResistance 1.0 2.0 3.0
printfn "%A" result // prints "Value 0.5454..."

let infiniteResult = totalResistance 1.0 0.0 3.0
printfn "%A" infiniteResult // prints "Infinite"

Of course this can be done with the Maybe monad as seen in https://github.com/panesofglass/FSharp.Monad/blob/master/tests/FSharp.Monad.Tests/MaybeTest.fs