Source file qv.ml

type t = Q.t [@@deriving compare]

exception NonsensicalQuotientValue of string

exception DenominatorZero of string

exception NonQuotientRep of string

module S = struct
  type showable = {value: string} [@@deriving show, yojson]

  let one () = Q.one

  let neg x = Q.neg x

  let abs x = Q.abs x

  let signum x = Q.sign x

  let add x y = Q.add x y

  let sub x y = Q.sub x y

  let mul x y = Q.mul x y

  let div x y = Q.div x y

  let make str =
    let pat = Re2.create_exn "^-?[0-9]*/?-?[0-9]*?$" in
    match Re2.matches pat str with
    | true -> (
        let q = Q.of_string str in
        match Q.classify q with
        | Q.INF | Q.MINF | Q.UNDEF ->
            raise
              (NonsensicalQuotientValue
                 "nonsensical quotient values are not suitable for currency \
                  operation" )
        | Q.NZERO ->
            if Z.compare q.den Z.zero = 0 then
              raise (DenominatorZero "denominator must not be zero")
            else q
        | Q.ZERO -> Q.zero )
    | false ->
        raise
          (NonQuotientRep
             "only quotient representation allowed, e.g. 123/456" )

  let num_of_q x = Q.num x

  let den_of_q x = Q.den x

  let to_str x =
    if Z.compare (den_of_q x) Z.one = 0 then Q.to_string x ^ "/1"
    else Q.to_string x

  let to_float x = Q.to_float x

  let to_json x =
    Yojson.Safe.to_string @@ showable_to_yojson {value= to_str x}
end