package safemoney

Signature for user-defined currency type. Typically one needs to provide the following:

• currency symbol
• currency description
• number of named scales with their value if any

To make custom type module simply implement the Custom signature:

module Custome_Type : Custom = struct
  let symbol = "CSTM"

  let description = "Custom Currency"

  let units =
    let table = Hashtbl.create (module String) in
    let scale1 = Discrete.Scale.make_scale symbol "scale1" (Utils.make_q "1/1") in
    let scale2 = Discrete.Scale.make_scale symbol "scale2" (Utils.make_q "100/1") in
    Hashtbl.set table ~key: "scale1" ~data: scale1;
    Hashtbl.set table ~key: "scale2" ~data: scale2;
    Some table

  let make_qv qv = Quotient.make_qv (symbol, qv)

  let make_dv unit dv =
    match units with
    | Some tbl -> let s = Option.value_exn ~message: "Error retriving non-existent scale" @@ Hashtbl.find tbl unit in Some (Discrete.make_dv (s, dv))
    | None -> None
end