F# RPN Calculator Computation Expression Builder!

rpnce.fsx

type CalcBuilder() =
  member __.Yield(()) = ()

  member __.Run((x, ())) = x

  [<CustomOperation("push")>]
  member __.Push(rest, x) = (x, rest) 
    
  [<CustomOperation("add")>]
  member __.Add((y, (x, rest))) = (x + y, rest)

  [<CustomOperation("sub")>]
  member __.Subtract((y, (x, rest))) = (x - y, rest)

  [<CustomOperation("mult")>]
  member __.Multiply((y, (x, rest))) = (x * y, rest)

  [<CustomOperation("div")>]
  member __.Divide((y, (x, rest))) = (x / y, rest)


let calc = CalcBuilder()

// Returns 1
calc {
  push 1
}

// Returns 9
calc {
  push 1
  push 2
  add
  push 3
  mult 
}

// Doesn't compile - more than one item on stack!
calc {
  push 1
  push 2
}