OCaml

5 files changed, 697 insertions, 0 deletions

diff --git a/lib/dune b/lib/dune
new file mode 100644
index 0000000..ff9a2ee
--- /dev/null
+++ b/lib/dune
@@ -0,0 +1,5 @@
+(library
+ (name rdcapsis)
+ (preprocess
+  (pps ppx_jane))
+ (libraries core zarith dmap delimited_parsing re core_unix.date_unix))
diff --git a/lib/iban.ml b/lib/iban.ml
new file mode 100644
index 0000000..6e47e9d
--- /dev/null
+++ b/lib/iban.ml
@@ -0,0 +1,87 @@
+open Core
+open Option.Let_syntax
+
+type t = string
+
+(* Modulo-97 arithmetic. Prevents us from having to use Zarith here. *)
+module M97 : sig
+  type t
+
+  val of_int : int -> t
+  val lt : t -> t -> bool
+  val equal : t -> t -> bool
+  val ( * ) : t -> t -> t
+  val ( + ) : t -> t -> t
+  val ( ~$ ) : int -> t
+end = struct
+  type t = int
+
+  let of_int x = x % 97
+  let equal = Int.( = )
+  let lt = Int.( < )
+  let ( * ) x y = x * y % 97
+  let ( + ) x y = (x + y) % 97
+  let ( ~$ ) = of_int
+end
+
+let m97_of_alnum c =
+  let v = Char.to_int c in
+  if Char.is_digit c then Some (M97.of_int (v - Char.to_int '0'))
+  else if Char.is_alpha c then
+    if Char.is_lowercase c then Some (M97.of_int (v - Char.to_int 'a' + 10))
+    else Some (M97.of_int (v - Char.to_int 'A' + 10))
+  else None
+
+let m97_of_digit c =
+  match m97_of_alnum c with Some v when M97.(lt v ~$10) -> Some v | _ -> None
+
+let m97_of_alpha c =
+  match m97_of_alnum c with
+  | Some v when not M97.(lt v ~$10) -> Some v
+  | _ -> None
+
+let string_fold_option ~(init : 'a) ~(f : 'a -> char -> 'a option) s =
+  let rec go i (acc : 'a) : 'a option =
+    if i >= String.length s then Some acc
+    else Option.(f acc (String.unsafe_get s i) >>= go (i + 1))
+  in
+  go 0 init
+
+let m97_of_iban s =
+  string_fold_option s ~init:`In_country1 ~f:(fun st c ->
+      match st with
+      | `In_country1 ->
+          let%map co1 = m97_of_alpha c in
+          `In_country2 co1
+      | `In_country2 co1 ->
+          let%map co2 = m97_of_alpha c in
+          `In_check1 M97.((co1 * ~$100) + co2)
+      | `In_check1 co ->
+          let%map ch1 = m97_of_digit c in
+          `In_check2 (co, ch1)
+      | `In_check2 (co, ch1) ->
+          let%map ch2 = m97_of_digit c in
+          `In_bban M97.(co, (ch1 * ~$10) + ch2, ~$0)
+      | `In_bban (co, ch, bban) ->
+          let%map v = m97_of_alnum c in
+          let bban' =
+            M97.(if lt v ~$10 then (bban * ~$10) + v else (bban * ~$100) + v)
+          in
+          `In_bban (co, ch, bban'))
+  |> function
+  | Some (`In_bban (co, ch, bban)) ->
+      Some M97.((bban * ~$1000000) + (co * ~$100) + ch)
+  | _ -> None
+
+let check_iban s =
+  String.length s <= 34 && Option.exists (m97_of_iban s) ~f:M97.(equal ~$1)
+
+let make s : t option = if check_iban s then Some s else None
+let to_string = Fn.id
+
+let of_string s =
+  match make s with
+  | Some iban -> iban
+  | None -> Printf.failwithf "Iban.of_string: %S" s ()
+
+let equal = String.equal
diff --git a/lib/iban.mli b/lib/iban.mli
new file mode 100644
index 0000000..944928c
--- /dev/null
+++ b/lib/iban.mli
@@ -0,0 +1,8 @@
+open Core
+
+type t
+
+val make : string -> t option
+
+include Stringable.S with type t := t
+include Equal.S with type t := t
diff --git a/lib/ingcsv.ml b/lib/ingcsv.ml
new file mode 100644
index 0000000..a8eba51
--- /dev/null
+++ b/lib/ingcsv.ml
@@ -0,0 +1,487 @@
+open Core
+module Time_ns = Time_ns_unix
+
+module Debit_credit = struct
+  type t = Debit | Credit
+
+  let of_string = function
+    | "Debit" -> Debit
+    | "Credit" -> Credit
+    | s -> Printf.failwithf "DebitCredit.of_string: %S" s ()
+
+  let to_string = function Debit -> "Debit" | Credit -> "Credit"
+end
+
+module Cents = struct
+  type t = Z.t
+
+  let of_string s =
+    (* TODO: consider being more bitchy here *)
+    String.lsplit2_exn s ~on:',' |> Tuple2.map ~f:Z.of_string
+    |> fun (high, low) -> Z.((high * ~$100) + low)
+end
+
+module Transaction_type = struct
+  type t =
+    | Accept_giro (* AC (acceptgiro) *)
+    | Atm_withdrawal (* GM (geldautomaat, Giromaat) *)
+    | Batch_payment (* VZ (verzamelbetaling); 'Batch payment' *)
+    | Branch_posting (* FL (filiaalboeking) *)
+    | Deposit (* ST (storting) *)
+    | Direct_debit (* IC (incasso); 'SEPA direct debit' *)
+    | Ideal (* ID (iDEAL); 'iDEAL' *)
+    | Online_banking (* GT (internetbankieren, Girotel); 'Online Banking' *)
+    | Office_withdrawal (* PK (opname kantoor, postkantoor) *)
+    | Payment_terminal (* BA (betaalautomaat); 'Payment terminal' *)
+    | Periodic_transfer (* PO (periodieke overschrijving) *)
+    | Phone_banking (* GF (telefonisch bankieren, Girofoon) *)
+    | Transfer (* OV (overboeking); 'Transfer' *)
+    | Various (* DV (diversen) *)
+  [@@deriving equal, string]
+
+  let of_code = function
+    | "AC" -> Accept_giro
+    | "GM" -> Atm_withdrawal
+    | "VZ" -> Batch_payment
+    | "FL" -> Branch_posting
+    | "ST" -> Deposit
+    | "IC" -> Direct_debit
+    | "ID" -> Ideal
+    | "GT" -> Online_banking
+    | "PK" -> Office_withdrawal
+    | "BA" -> Payment_terminal
+    | "PO" -> Periodic_transfer
+    | "GF" -> Phone_banking
+    | "OV" -> Transfer
+    | "DV" -> Various
+    | s -> Printf.failwithf "TransactionType.of_code: %S" s ()
+
+  let of_type = function
+    | "SEPA direct debit" -> Direct_debit
+    | "Batch payment" -> Batch_payment
+    | "Online Banking" -> Online_banking
+    | "Payment terminal" -> Payment_terminal
+    | "Transfer" -> Transfer
+    | "iDEAL" -> Ideal
+    | s -> Printf.failwithf "TransactionType.of_type: %S" s ()
+end
+
+module Primitive_tx = struct
+  type t = {
+    date : Date.t;
+    description : string;
+    account : Iban.t;
+    counterparty : Iban.t option;
+    type_ : Transaction_type.t;
+    debit_credit : Debit_credit.t;
+    amount : Cents.t;
+    notifications : string;
+    resulting_balance : Cents.t;
+    tag : string;
+  }
+  [@@deriving fields]
+
+  let opt_field (f : string -> 'a) (v : string) : 'a option =
+    if String.is_empty (String.strip v) then None else Some (f v)
+
+  let parse : t Delimited.Read.t =
+    let open Delimited.Read.Let_syntax in
+    let%map_open date = at_header "Date" ~f:Date.of_string
+    and description = at_header "Name / Description" ~f:Fn.id
+    and account = at_header "Account" ~f:Iban.of_string
+    and counterparty = at_header "Counterparty" ~f:(opt_field Iban.of_string)
+    and code = at_header "Code" ~f:Transaction_type.of_code
+    and debit_credit = at_header "Debit/credit" ~f:Debit_credit.of_string
+    and amount = at_header "Amount (EUR)" ~f:Cents.of_string
+    and type_ = at_header "Transaction type" ~f:Transaction_type.of_type
+    and notifications = at_header "Notifications" ~f:Fn.id
+    and resulting_balance = at_header "Resulting balance" ~f:Cents.of_string
+    and tag = at_header "Tag" ~f:Fn.id in
+    if not ([%equal: Transaction_type.t] code type_) then
+      Printf.failwithf
+        "Primitive_tx.parse: parsed transaction code (%S) and type (%S) do not \
+         match"
+        (Transaction_type.to_string code)
+        (Transaction_type.to_string type_)
+        ();
+    {
+      date;
+      description;
+      account;
+      counterparty;
+      type_;
+      debit_credit;
+      amount;
+      notifications;
+      resulting_balance;
+      tag;
+    }
+end
+
+type tx_base = {
+  date : Date.t;
+  account : Iban.t;
+  amount : Cents.t;
+  res_bal : Cents.t;
+  tag : string;
+}
+
+type tx_specifics =
+  | Payment_terminal_payment of {
+      counterparty_name : string;
+      card_sequence_no : string;
+      timestamp : Time_ns.t;
+      transaction : string;
+      terminal : string;
+      google_pay : bool;
+    }
+  | Payment_terminal_cashback of {
+      counterparty_name : string;
+      card_sequence_no : string;
+      timestamp : Time_ns.t;
+      transaction : string;
+      terminal : string;
+    }
+  | Online_banking_credit of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      timestamp : Time_ns.t;
+    }
+  | Online_banking_debit of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      mtimestamp : Time_ns.t option;
+    }
+  | Recurrent_direct_debit of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      reference : string;
+      mandate_id : string;
+      creditor_id : string;
+      other_party : string option;
+    }
+  | Rounding_savings_deposit of { savings_account : string }
+  | Deposit of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      reference : string;
+    }
+  | Ideal_debit of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      timestamp : Time_ns.t;
+      reference : string;
+    }
+  | Batch_payment of {
+      counterparty_name : string;
+      counterparty_iban : Iban.t;
+      description : string;
+      reference : string;
+    }
+
+type tx = Tx of tx_base * tx_specifics
+
+let assert_value_date (ptx : Primitive_tx.t) s =
+  let val_date = Date_unix.parse s ~fmt:"%d/%m/%Y" in
+  if not Date.(val_date = ptx.date) then
+    failwith
+      "assert_value_date: expected transaction date and value date to be the \
+       same"
+
+let[@warning "-8"] specifics_from_prim_exn (ams_tz : Time_ns.Zone.t) :
+    Primitive_tx.t -> tx_specifics = function
+  | { type_ = Payment_terminal; debit_credit = Debit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Card sequence no.: ([0-9]+) ? ([0-9]{2}/[0-9]{2}/[0-9]{4} \
+           [0-9]{2}:[0-9]{2}) Transaction: (.*) Term: ((.+) Google Pay|(.+)) \
+           Value date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [|
+        _;
+        card_seq_no;
+        timestamp_str;
+        transaction;
+        _;
+        gpay_term;
+        no_gpay_term;
+        val_date_str;
+      |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let timestamp =
+        Time_ns.parse timestamp_str ~allow_trailing_input:false
+          ~fmt:"%d/%m/%Y %H:%M" ~zone:ams_tz
+      in
+      Payment_terminal_payment
+        {
+          counterparty_name = ptx.description;
+          card_sequence_no = card_seq_no;
+          timestamp;
+          transaction;
+          terminal =
+            (if String.is_empty gpay_term then no_gpay_term else gpay_term);
+          google_pay = String.is_empty no_gpay_term;
+        }
+  | { type_ = Payment_terminal; debit_credit = Credit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Card sequence no.: ([0-9]+) ? ([0-9]{2}/[0-9]{2}/[0-9]{4} \
+           [0-9]{2}:[0-9]{2}) Transaction: (.*) Term: (.*) Cashback \
+           transaction Value date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; card_seq_no; timestamp_str; transaction; term; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let timestamp =
+        Time_ns.parse timestamp_str ~allow_trailing_input:false
+          ~fmt:"%d/%m/%Y %H:%M" ~zone:ams_tz
+      in
+      Payment_terminal_cashback
+        {
+          counterparty_name = ptx.description;
+          card_sequence_no = card_seq_no;
+          timestamp;
+          transaction;
+          terminal = term;
+        }
+  | { type_ = Online_banking; debit_credit = Credit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) Date/time: \
+           ([0-9]{2}-[0-9]{2}-[0-9]{4} [0-9]{2}:[0-9]{2}:[0-9]{2}) Value date: \
+           ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; name; desc; iban_str; timestamp_str; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let iban = Iban.of_string iban_str
+      and timestamp =
+        Time_ns.parse timestamp_str ~allow_trailing_input:false
+          ~fmt:"%d-%m-%Y %H:%M:%S" ~zone:ams_tz
+      in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Online_banking/Credit): expected counterparty \
+           name to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Online_banking/Credit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Online_banking_credit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          timestamp;
+        }
+  | { type_ = Online_banking; debit_credit = Debit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) (Date/time: \
+           ([0-9]{2}-[0-9]{2}-[0-9]{4} [0-9]{2}:[0-9]{2}:[0-9]{2}) )?Value \
+           date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; name; desc; iban_str; _; timestamp_str; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let iban = Iban.of_string iban_str
+      and mtimestamp =
+        if String.is_empty timestamp_str then None
+        else
+          Some
+            (Time_ns.parse timestamp_str ~allow_trailing_input:false
+               ~fmt:"%d-%m-%Y %H:%M:%S" ~zone:ams_tz)
+      in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Online_banking/Debit): expected counterparty \
+           name to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Online_banking/Debit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Online_banking_debit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          mtimestamp;
+        }
+  | { type_ = Direct_debit; debit_credit = Debit; _ } as ptx
+    when String.is_suffix ptx.notifications
+           ~suffix:"Recurrent SEPA direct debit" ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.* ING Verzekeren) Description: (.*) IBAN: ([A-Z0-9]+) \
+           Reference: (.*) Mandate ID: (.*) Creditor ID: (.*) Recurrent SEPA \
+           direct debit$"
+      in
+      let [| _; name; desc; iban_str; ref_; mandate_id; creditor_id |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      let iban = Iban.of_string iban_str in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Direct_debit/Debit): expected counterparty \
+           name to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Direct_debit/Debit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Recurrent_direct_debit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          reference = ref_;
+          mandate_id;
+          creditor_id;
+          other_party = None;
+        }
+  | { type_ = Direct_debit; debit_credit = Debit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) Reference: (.*) \
+           Mandate ID: (.*) Creditor ID: (.*) Recurrent SEPA direct debit \
+           (Other party: (.*) )?Value date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [|
+        _;
+        name;
+        desc;
+        iban_str;
+        ref_;
+        mandate_id;
+        creditor_id;
+        _;
+        other_party;
+        val_date_str;
+      |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let iban = Iban.of_string iban_str in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Direct_debit/Debit): expected counterparty \
+           name to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Direct_debit/Debit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Recurrent_direct_debit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          reference = ref_;
+          mandate_id;
+          creditor_id;
+          other_party =
+            (if String.is_empty other_party then None else Some other_party);
+        }
+  | { type_ = Transfer; debit_credit = Credit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) Reference: (.*) \
+           Value date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; name; desc; iban_str; ref_; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let iban = Iban.of_string iban_str in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Transfer/Credit): expected counterparty name \
+           to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Direct_debit/Debit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Deposit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          reference = ref_;
+        }
+  | { type_ = Transfer; debit_credit = Debit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^To Oranje spaarrekening ([A-Z0-9]+) Afronding Value date: \
+           ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; savings_account; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      Rounding_savings_deposit { savings_account }
+  | { type_ = Ideal; debit_credit = Debit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) Reference: \
+           ([0-9]{2}-[0-9]{2}-[0-9]{4} [0-9]{2}:[0-9]{2}) ([0-9]+) Value date: \
+           ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; name; desc; iban_str; timestamp_str; ref_; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let timestamp =
+        Time_ns.parse timestamp_str ~allow_trailing_input:false
+          ~fmt:"%d-%m-%Y %H:%M" ~zone:ams_tz
+      in
+      let iban = Iban.of_string iban_str in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Ideal/Debit): expected counterparty name to \
+           match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Ideal/Debit): expected IBAN to match and \
+           primitive counterparty IBAN";
+      Ideal_debit
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          timestamp;
+          reference = ref_;
+        }
+  | { type_ = Batch_payment; debit_credit = Credit; _ } as ptx ->
+      let regex =
+        Re.Pcre.regexp
+          "^Name: (.*) Description: (.*) IBAN: ([A-Z0-9]+) Reference: (.*) \
+           Value date: ([0-9]{2}/[0-9]{2}/[0-9]{4})$"
+      in
+      let [| _; name; desc; iban_str; ref_; val_date_str |] =
+        Re.Pcre.extract ~rex:regex ptx.notifications
+      in
+      assert_value_date ptx val_date_str;
+      let iban = Iban.of_string iban_str in
+      if not String.(name = ptx.description) then
+        failwith
+          "specifics_from_prim (Batch_payment/Credit): expected counterparty \
+           name to match primitive description";
+      if not (Option.equal Iban.equal (Some iban) ptx.counterparty) then
+        failwith
+          "specifics_from_prim (Batch_payment/Credit): expected IBAN to match \
+           and primitive counterparty IBAN";
+      Batch_payment
+        {
+          counterparty_name = name;
+          counterparty_iban = iban;
+          description = desc;
+          reference = ref_;
+        }
diff --git a/lib/ledger.ml b/lib/ledger.ml
new file mode 100644
index 0000000..fd1b2a9
--- /dev/null
+++ b/lib/ledger.ml
@@ -0,0 +1,110 @@
+open Core
+
+type account_type = Asset | Equity | Liability | Expense | Income
+
+type tx_type =
+  | Interest_tx
+  | Online_banking_tx
+  | Recurrent_direct_tx
+  | Payment_terminal_tx
+  | Cash_payment_tx
+  | Atm_tx
+  | Auto_save_rounding_tx
+  | Batch_tx
+  | Direct_debit_tx
+  | Periodic_tx
+
+type iban_tag = Account_tag | Counterparty_iban_tag [@@deriving compare]
+
+type unit_tag = Filed_tag | GooglePay_tag | AutoRoundSavings_tag
+[@@deriving compare]
+
+type string_tag =
+  | Desc_tag
+  | User_tag
+  | Counterparty_name_tag
+  | Reference_tag
+  | Mandate_id_tag
+  | Creditor_id_tag
+  | Other_party_tag
+  | Transaction_tag
+  | Terminal_tag
+  | Card_seq_no_tag
+  | Savings_account_tag
+[@@deriving compare]
+
+module Label = struct
+  type 'a t =
+    | Iban_label : iban_tag -> Iban.t t
+    | String_label : string_tag -> string t
+    | Timestamp_label : Time_ns.t t
+    | Unit_label : unit_tag -> unit t
+
+  let int_to_cmp x : ('a, 'a) Dmap.cmp =
+    if x < 0 then Lt else if x > 0 then Gt else Eq
+
+  let compare (type a1 a2) (v1 : a1 t) (v2 : a2 t) : (a1, a2) Dmap.cmp =
+    match (v1, v2) with
+    | Iban_label t1, Iban_label t2 -> int_to_cmp @@ [%compare: iban_tag] t1 t2
+    | String_label t1, String_label t2 ->
+        int_to_cmp @@ [%compare: string_tag] t1 t2
+    | Timestamp_label, Timestamp_label -> Eq
+    | Unit_label t1, Unit_label t2 -> int_to_cmp @@ [%compare: unit_tag] t1 t2
+    | Iban_label _, _ -> Lt
+    | String_label _, Iban_label _ -> Gt
+    | String_label _, _ -> Lt
+    | Timestamp_label, Unit_label _ -> Lt
+    | Timestamp_label, _ -> Gt
+    | Unit_label _, _ -> Gt
+end
+
+module Labels = Dmap.Make (Label)
+
+module Money : sig
+  type t
+
+  val equal : t -> t -> bool
+  val compare : t -> t -> int
+  val of_z : Z.t -> t
+  val to_z : t -> Z.t
+  val ( + ) : t -> t -> t
+  val ( - ) : t -> t -> t
+end = struct
+  type t = Z.t
+
+  let equal = Z.equal
+  let compare = Z.compare
+  let of_z = Fn.id
+  let to_z = Fn.id
+  let ( + ) x y = Z.(x + y)
+  let ( - ) x y = Z.(x - y)
+end
+
+type scalar = Amount of Money.t | Rate of Z.t [@@deriving equal, compare]
+type account_id = string list
+type commodity_id = string (* TODO: consider making this UUID *)
+
+type account = {
+  id : account_id;
+  description : string list;
+  commodity_id : commodity_id;
+  balance : Money.t;
+}
+
+type bal_assert = { account : account_id; amount : Money.t; labels : Labels.t }
+
+module Account_id_key = struct
+  type t = account_id
+  type comparator_witness
+end
+
+type tx = {
+  cleared : Date.t option;
+  commodity_id : commodity_id;
+  debit : scalar Map.M(Account_id_key).t;
+  credit : scalar Map.M(Account_id_key).t;
+  labels : Labels.t;
+}
+
+type item = Tx_item of tx | Bal_assert_item of bal_assert
+type ledger = Ledger of item list