Units of measure magic

gistfile1.txt

let inline retype  (t : ^t) :^tm = (# "" t : ^tm #)
let inline (++) (w : ^W when ^W : (static member IsMeasureAbbrev : ^tm * ^t -> unit)) (t : ^t) = (# "" t : ^tm #)
open System

[<MeasureAnnotatedAbbreviation>]
type Guid<[<Measure>] 'Measure> = Guid

[<MeasureAnnotatedAbbreviation>]
type string<[<Measure>] 'Measure> = string

type UoM = 
    | UoM
    static member IsMeasureAbbrev(_ : Guid<'Measure>, _ : Guid) = ()
    static member IsMeasureAbbrev(_ : string<'Measure>, _ : string) = ()

[<Measure>]
type processId

[<Measure>]
type taskId

type Entry = 
    { ProcessId : Guid<processId>
      TaskId : Guid<taskId> }

let (taskId : Guid<taskId>) = UoM ++ Guid.NewGuid()
let (pid : Guid<processId>) = UoM ++ Guid.NewGuid()

let entry = 
    { ProcessId = pid
      TaskId = taskId }



[<EntryPoint>]
let main argv = 

    let (taskId : Guid<taskId>) = UoM ++ Guid.NewGuid()
    let (pid : Guid<processId>) = UoM ++ Guid.NewGuid()

    let good ={ProcessId = retype (Guid.NewGuid()); TaskId = retype (Guid.NewGuid())} 

    let evil ={ProcessId = retype (Guid.NewGuid()); TaskId = retype (false)} 
    printfn "%A" argv
    0 // return an integer exit code