1 files changed, 384 insertions, 378 deletions

diff --git a/lib/ledger.ml b/lib/ledger.ml
index 87f3ead..9d315ae 100644
--- a/lib/ledger.ml
+++ b/lib/ledger.ml
@@ -182,7 +182,7 @@ type scalar =
   | Rate of { in_primary_commodity : Money.Amount.t; rate : Bigdecimal.t }
 [@@deriving equal, compare, sexp_of] *)
 
-module Account_structure0 = struct
+module Account_structure = struct
   module Categories = struct
     (* The five top-level categories *)
     type asset [@@deriving sexp_of]
@@ -198,11 +198,35 @@ module Account_structure0 = struct
     type final [@@deriving sexp_of]
   end
 
-  module type Scaffold = sig
+  module type S = sig
     type 'a t [@@deriving sexp_of]
+
+    type 'a f =
+      | Accounts_payable : Categories.final f t -> Categories.liability f
+      | Accounts_receivable : Categories.final f t -> Categories.asset f
+      | Bank : Categories.bank f t -> Categories.asset f
+      | Cash : Categories.final f t -> Categories.asset f
+      | Credit : Categories.final f t -> Categories.liability f
+      | Mutual_fund : Categories.final f t -> Categories.asset f
+      | Stock : Categories.final f t -> Categories.asset f
+      | Savings : Categories.final f t -> Categories.bank f
+      | Checking : Categories.final f t -> Categories.bank f
+    [@@deriving sexp_of]
+
+    type t0 =
+      | Asset of Categories.asset f t
+      | Equity of Categories.equity f t
+      | Expense of Categories.expense f t
+      | Income of Categories.income f t
+      | Liability of Categories.liability f t
+    [@@deriving sexp_of]
   end
 
-  module Make (F : Scaffold) = struct
+  module Make (F : sig
+    type 'a t [@@deriving sexp_of]
+  end) : S with type 'a t = 'a F.t = struct
+    include F
+
     type 'a f =
       | Accounts_payable : Categories.final f F.t -> Categories.liability f
       | Accounts_receivable : Categories.final f F.t -> Categories.asset f
@@ -225,40 +249,35 @@ module Account_structure0 = struct
   end
 
   module Gen_f_cons = struct
-    module type S = sig
-      type inner
-      type outer
-
-      module Specialize : functor
-        (F : Scaffold)
-        (G : module type of Make (F))
-        -> sig
-        val cons : inner G.f F.t -> outer G.f
-      end
-    end
-
     module Accounts_payable = struct
       type outer = Categories.liability
       type inner = Categories.final
 
-      module Specialize (F : Scaffold) (G : module type of Make (F)) = struct
+      module Specialize (G : S) = struct
         let cons v = G.Accounts_payable v
       end
+    end
+
+    module type S = sig
+      type inner
+      type outer
+
+      module Specialize : functor (G : S) -> sig
+        val cons : inner G.f G.t -> outer G.f
       end
     end
+  end
 
   module Visitor
-      (F : Scaffold)
-      (G :
-        module type of Make (F))
-          (Acc : sig
-            type 'a t
-          end) =
+      (G : S)
+      (Acc : sig
+        type 'a t
+      end) =
   struct
     type nonrec 'outer t = {
       car :
         'inner.
-        'inner G.f F.t ->
+        'inner G.f G.t ->
         (module Gen_f_cons.S with type inner = 'inner and type outer = 'outer) ->
         'outer Acc.t;
     }
@@ -278,249 +297,236 @@ module Account_structure0 = struct
       | Checking v -> f.car v (fun inner -> H.Checking inner) *)
   end
 
-  module Basic_visitor (F : Scaffold) (G : module type of Make (F)) = struct
-    type nonrec 'b t = { car : 'a. 'a G.f F.t -> 'b }
+  module Basic_visitor (G : S) = struct
+    type nonrec 'b t = { car : 'a. 'a G.f G.t -> 'b }
 
     let visit (type b c) (f : c t) : b G.f -> c =
       let module Inst =
-        Visitor (F) (G)
+        Visitor
+          (G)
           (struct
             type 'a t = c
           end)
       in
       Inst.visit { car = (fun v _cons -> f.car v) }
   end
-  end
+end
 
-  module Account_type = struct
-    type 'a elem = Leaf | Node of 'a [@@deriving sexp_of]
+module Account_type = struct
+  type 'a elem = Leaf | Node of 'a [@@deriving sexp_of]
 
-    module Scaffold = struct
-      type 'a t = 'a elem [@@deriving sexp_of]
-    end
+  include Account_structure.Make (struct
+    type 'a t = 'a elem [@@deriving sexp_of]
+  end)
+end
 
-    include Account_structure0.Make (Scaffold)
-  end
+module Typed_account_path = struct
+  type 'a elem = Leaf | Node of string * 'a | Ind of string * 'a elem
+  [@@deriving sexp_of]
 
-  module Account_structure (F : Account_structure0.Scaffold) = struct
-    module Structure = Account_structure0.Make (F)
-    include Structure
-
-    module Mapper = struct
-      type nonrec 'b t = {
-        car :
-          'a.
-          'a f F.t ->
-          ('a Account_type.f Account_type.elem -> Account_type.t0) ->
-          ('b * 'a f F.t) option;
-      }
-
-      let map (type b c) (f : c t) (mkt : b Account_type.f -> Account_type.t0) :
-          b f -> (c * b f) option =
-        let module Inst =
-          Account_structure0.Visitor (F) (Structure)
-            (struct
-              type 'b t = (c * 'b f) option
-            end)
-        in
-        Inst.visit
-          {
-            car =
-              (fun (type inner)
-                v
-                (module Gen_cons : Account_structure0.Gen_f_cons.S
-                  with type inner = inner
-                   and type outer = b)
-              ->
-                let open Option.Let_syntax in
-                let module Type_cons =
-                  Gen_cons.Specialize (Account_type.Scaffold) (Account_type)
-                in
-                let module Own_cons = Gen_cons.Specialize (F) (Structure) in
-                let%map c, v' = f.car v (fun el -> mkt (Type_cons.cons el)) in
-                (c, Own_cons.cons v'));
-          }
-    end
-  end
+  include Account_structure.Make (struct
+    type 'a t = 'a elem [@@deriving sexp_of]
+  end)
+end
 
-  module Typed_account_path = struct
-    type 'a elem = Leaf | Node of string * 'a | Ind of string * 'a elem
-    [@@deriving sexp_of]
+module Account_path = struct
+  type t = string list [@@deriving compare, sexp]
 
-    include Account_structure (struct
-      type 'a t = 'a elem [@@deriving sexp_of]
-    end)
-  end
+  module Map = Map.Make (struct
+    type nonrec t = t [@@deriving compare, sexp]
+  end)
+end
 
-  module Account_path = struct
-    type t = string list [@@deriving compare, sexp]
+module Account_hierarchy = struct
+  (* The contents of an account of category 'a *)
+  type 'a core =
+    (* Comprises of subaccounts of its subcategories *)
+    | Node of 'a String.Map.t
+    (* Comprises of subaccounts of its own category *)
+    | Ind of 'a account String.Map.t
+    (* Has no subaccounts, has a balance in a certain commodity *)
+    | Leaf of Commodity_id.t * Money.Diff.t
+  [@@deriving sexp_of]
 
-    module Map = Map.Make (struct
-      type nonrec t = t [@@deriving compare, sexp]
-    end)
-  end
+  and extra = { description : String.t } [@@deriving sexp_of]
+  and 'a account = extra * 'a core
 
-  module Account_hierarchy = struct
-    (* The contents of an account of category 'a *)
-    type 'a core =
-      (* Comprises of subaccounts of its subcategories *)
-      | Node of 'a String.Map.t
-      (* Comprises of subaccounts of its own category *)
-      | Ind of 'a account String.Map.t
-      (* Has no subaccounts, has a balance in a certain commodity *)
-      | Leaf of Commodity_id.t * Money.Diff.t
-    [@@deriving sexp_of]
+  module Structure = Account_structure.Make (struct
+    type 'a t = 'a account [@@deriving sexp_of]
+  end)
 
-    and extra = { description : String.t } [@@deriving sexp_of]
-    and 'a account = extra * 'a core
+  (* All accounts *)
+  type world = Structure.t0 String.Map.t
 
-    module Scaffold = struct
-      type 'a t = 'a account [@@deriving sexp_of]
-    end
+  module Mapper = struct
+    type nonrec 'b t = {
+      car :
+        'a.
+        'a Structure.f account ->
+        ('a Account_type.f Account_type.elem -> Account_type.t0) ->
+        ('b * 'a Structure.f account) option;
+    }
 
-    module Structure = Account_structure (Scaffold)
-
-    (* All accounts *)
-    type world = Structure.t0 String.Map.t
-
-    let rec unsafe_alter_aux (subaid : Account_path.t)
-        (f :
-          Account_type.t0 ->
-          extra ->
-          Commodity_id.t ->
-          Money.Diff.t ->
-          'a * extra * Money.Diff.t) : 'a Structure.Mapper.t =
-      {
-        car =
-          (fun in_acc mkt ->
-            let open Option.Let_syntax in
-            match (subaid, in_acc) with
-            | [], (extra, Leaf (acc_comm, acc_bal)) ->
-                let x, extra', acc_bal' =
-                  f (mkt Account_type.Leaf) extra acc_comm acc_bal
-                in
-                Some (x, (extra', Leaf (acc_comm, acc_bal')))
-            | [], _ -> None
-            | subaid0 :: subaid, (extra, Node subaccs) ->
-                let%bind subacc = Map.find subaccs subaid0 in
-                let%map x, subacc' =
-                  Structure.Mapper.map
-                    (unsafe_alter_aux subaid f)
-                    (fun k -> mkt (Node k))
-                    subacc
-                in
-                (x, (extra, Node (Map.set subaccs ~key:subaid0 ~data:subacc')))
-            | subaid0 :: subaid, (extra, Ind subaccs) ->
-                let%bind subacc = Map.find subaccs subaid0 in
-                let%map x, subacc' =
-                  (unsafe_alter_aux subaid f).car subacc mkt
-                in
-                (x, (extra, Ind (Map.set subaccs ~key:subaid0 ~data:subacc')))
-            | _ :: _, (_, Leaf _) -> None);
-      }
-
-    let unsafe_alter (aid : Account_path.t)
-        (f :
-          Account_type.t0 ->
-          extra ->
-          Commodity_id.t ->
-          Money.Diff.t ->
-          'a * extra * Money.Diff.t) (w : world) : ('a * world) option =
-      match aid with
-      | [] -> None
-      | aid0 :: subaid -> (
+    let map (type b c) (f : c t) (mkt : b Account_type.f -> Account_type.t0) :
+        b Structure.f -> (c * b Structure.f) option =
+      let module Inst =
+        Account_structure.Visitor
+          (Structure)
+          (struct
+            type 'b t = (c * 'b Structure.f) option
+          end)
+      in
+      Inst.visit
+        {
+          car =
+            (fun (type inner)
+              v
+              (module Gen_cons : Account_structure.Gen_f_cons.S
+                with type inner = inner
+                 and type outer = b)
+            ->
+              let open Option.Let_syntax in
+              let module Type_cons = Gen_cons.Specialize (Account_type) in
+              let module Own_cons = Gen_cons.Specialize (Structure) in
+              let%map c, v' = f.car v (fun el -> mkt (Type_cons.cons el)) in
+              (c, Own_cons.cons v'));
+        }
+  end
+
+  let rec unsafe_alter_aux (subaid : Account_path.t)
+      (f :
+        Account_type.t0 ->
+        extra ->
+        Commodity_id.t ->
+        Money.Diff.t ->
+        'a * extra * Money.Diff.t) : 'a Mapper.t =
+    {
+      car =
+        (fun in_acc mkt ->
           let open Option.Let_syntax in
-          match%bind Map.find w aid0 with
-          | Asset acc ->
-              let%map x, acc' =
-                (unsafe_alter_aux subaid f).car acc (fun k -> Asset k)
-              in
-              (x, Map.set w ~key:aid0 ~data:(Asset acc'))
-          | Expense acc ->
-              let%map x, acc' =
-                (unsafe_alter_aux subaid f).car acc (fun k -> Expense k)
-              in
-              (x, Map.set w ~key:aid0 ~data:(Expense acc'))
-          | Income acc ->
-              let%map x, acc' =
-                (unsafe_alter_aux subaid f).car acc (fun k -> Income k)
+          match (subaid, in_acc) with
+          | [], (extra, Leaf (acc_comm, acc_bal)) ->
+              let x, extra', acc_bal' =
+                f (mkt Account_type.Leaf) extra acc_comm acc_bal
               in
-              (x, Map.set w ~key:aid0 ~data:(Income acc'))
-          | Liability acc ->
-              let%map x, acc' =
-                (unsafe_alter_aux subaid f).car acc (fun k -> Liability k)
-              in
-              (x, Map.set w ~key:aid0 ~data:(Liability acc'))
-          | Equity acc ->
-              let%map x, acc' =
-                (unsafe_alter_aux subaid f).car acc (fun k -> Equity k)
-              in
-              (x, Map.set w ~key:aid0 ~data:(Equity acc')))
-
-    (** Update the balance (debit/credit ([dc])) of account [aid] [by_amount]
-        (commodity: [in_comm]) in [world], giving the updated world and the pre
-        and post balances for [aid] iff the account exists in [world]. *)
-    let update_bal aid dc by_amount in_comm (w : world) :
-        (Money.Diff.t * Money.Diff.t * world) option =
-      let open Option.Let_syntax in
-      let%bind mres, w' =
-        unsafe_alter aid
-          (fun acc_type acc_extra acc_comm acc_bal ->
-            if not ([%equal: Commodity_id.t] acc_comm in_comm) then
-              (None, acc_extra, acc_bal)
-            else
-              let on_debit =
-                match acc_type with
-                | Asset _ -> `Incr
-                | Expense _ -> `Incr
-                | Income _ -> `Decr
-                | Liability _ -> `Decr
-                | Equity _ -> `Decr
-              in
-              let acc_bal' =
-                Money.Diff.(acc_bal + of_amount by_amount dc ~on_debit)
-              in
-              (Some (acc_bal, acc_bal'), acc_extra, acc_bal'))
-          w
-      in
-      let%map pre_bal, post_bal = mres in
-      (pre_bal, post_bal, w')
-
-    let get_bal aid (w : world) : (Commodity_id.t * Money.Diff.t) option =
-      let open Option.Let_syntax in
-      let%map cb, _world' =
-        unsafe_alter aid
-          (fun _acc_type acc_extra acc_comm acc_bal ->
-            ((acc_comm, acc_bal), acc_extra, acc_bal))
-          w
-      in
-      cb
-
-    let add_balance_maps m1 m2 : Money.Diff.t Commodity_id.Map.t =
-      Map.merge m1 m2 ~f:(fun ~key:_comm -> function
-        | `Both (b1, b2) -> Some Money.Diff.(b1 + b2)
-        | `Left b | `Right b -> Some b)
-
-    let rec collect_balances : type a.
-        a Structure.f account -> Money.Diff.t Commodity_id.Map.t = function
-      | _extra, Leaf (acc_comm, acc_bal) ->
-          Commodity_id.Map.singleton acc_comm acc_bal
-      | _extra, Ind subaccs ->
-          Map.fold subaccs ~init:Commodity_id.Map.empty
-            ~f:(fun ~key:_ ~data:subacc comm_bal_sums ->
-              add_balance_maps comm_bal_sums (collect_balances subacc))
-      | _extra, Node subaccs ->
-          Map.fold subaccs ~init:Commodity_id.Map.empty
-            ~f:(fun ~key:_ ~data:subacc comm_bal_sums ->
-              let module Visitor =
-                Account_structure0.Basic_visitor (Scaffold) (Structure)
+              Some (x, (extra', Leaf (acc_comm, acc_bal')))
+          | [], _ -> None
+          | subaid0 :: subaid, (extra, Node subaccs) ->
+              let%bind subacc = Map.find subaccs subaid0 in
+              let%map x, subacc' =
+                Mapper.map
+                  (unsafe_alter_aux subaid f)
+                  (fun k -> mkt (Node k))
+                  subacc
               in
-              add_balance_maps comm_bal_sums
-                (Visitor.visit { car = collect_balances } subacc))
-
-    type delete_error = Not_found | Nonzero_balance
+              (x, (extra, Node (Map.set subaccs ~key:subaid0 ~data:subacc')))
+          | subaid0 :: subaid, (extra, Ind subaccs) ->
+              let%bind subacc = Map.find subaccs subaid0 in
+              let%map x, subacc' = (unsafe_alter_aux subaid f).car subacc mkt in
+              (x, (extra, Ind (Map.set subaccs ~key:subaid0 ~data:subacc')))
+          | _ :: _, (_, Leaf _) -> None);
+    }
 
-    (*
+  let unsafe_alter (aid : Account_path.t)
+      (f :
+        Account_type.t0 ->
+        extra ->
+        Commodity_id.t ->
+        Money.Diff.t ->
+        'a * extra * Money.Diff.t) (w : world) : ('a * world) option =
+    match aid with
+    | [] -> None
+    | aid0 :: subaid -> (
+        let open Option.Let_syntax in
+        match%bind Map.find w aid0 with
+        | Asset acc ->
+            let%map x, acc' =
+              (unsafe_alter_aux subaid f).car acc (fun k -> Asset k)
+            in
+            (x, Map.set w ~key:aid0 ~data:(Asset acc'))
+        | Expense acc ->
+            let%map x, acc' =
+              (unsafe_alter_aux subaid f).car acc (fun k -> Expense k)
+            in
+            (x, Map.set w ~key:aid0 ~data:(Expense acc'))
+        | Income acc ->
+            let%map x, acc' =
+              (unsafe_alter_aux subaid f).car acc (fun k -> Income k)
+            in
+            (x, Map.set w ~key:aid0 ~data:(Income acc'))
+        | Liability acc ->
+            let%map x, acc' =
+              (unsafe_alter_aux subaid f).car acc (fun k -> Liability k)
+            in
+            (x, Map.set w ~key:aid0 ~data:(Liability acc'))
+        | Equity acc ->
+            let%map x, acc' =
+              (unsafe_alter_aux subaid f).car acc (fun k -> Equity k)
+            in
+            (x, Map.set w ~key:aid0 ~data:(Equity acc')))
+
+  (** Update the balance (debit/credit ([dc])) of account [aid] [by_amount]
+      (commodity: [in_comm]) in [world], giving the updated world and the pre
+      and post balances for [aid] iff the account exists in [world]. *)
+  let update_bal aid dc by_amount in_comm (w : world) :
+      (Money.Diff.t * Money.Diff.t * world) option =
+    let open Option.Let_syntax in
+    let%bind mres, w' =
+      unsafe_alter aid
+        (fun acc_type acc_extra acc_comm acc_bal ->
+          if not ([%equal: Commodity_id.t] acc_comm in_comm) then
+            (None, acc_extra, acc_bal)
+          else
+            let on_debit =
+              match acc_type with
+              | Asset _ -> `Incr
+              | Expense _ -> `Incr
+              | Income _ -> `Decr
+              | Liability _ -> `Decr
+              | Equity _ -> `Decr
+            in
+            let acc_bal' =
+              Money.Diff.(acc_bal + of_amount by_amount dc ~on_debit)
+            in
+            (Some (acc_bal, acc_bal'), acc_extra, acc_bal'))
+        w
+    in
+    let%map pre_bal, post_bal = mres in
+    (pre_bal, post_bal, w')
+
+  let get_bal aid (w : world) : (Commodity_id.t * Money.Diff.t) option =
+    let open Option.Let_syntax in
+    let%map cb, _world' =
+      unsafe_alter aid
+        (fun _acc_type acc_extra acc_comm acc_bal ->
+          ((acc_comm, acc_bal), acc_extra, acc_bal))
+        w
+    in
+    cb
+
+  let add_balance_maps m1 m2 : Money.Diff.t Commodity_id.Map.t =
+    Map.merge m1 m2 ~f:(fun ~key:_comm -> function
+      | `Both (b1, b2) -> Some Money.Diff.(b1 + b2)
+      | `Left b | `Right b -> Some b)
+
+  let rec collect_balances : type a.
+      a Structure.f account -> Money.Diff.t Commodity_id.Map.t = function
+    | _extra, Leaf (acc_comm, acc_bal) ->
+        Commodity_id.Map.singleton acc_comm acc_bal
+    | _extra, Ind subaccs ->
+        Map.fold subaccs ~init:Commodity_id.Map.empty
+          ~f:(fun ~key:_ ~data:subacc comm_bal_sums ->
+            add_balance_maps comm_bal_sums (collect_balances subacc))
+    | _extra, Node subaccs ->
+        Map.fold subaccs ~init:Commodity_id.Map.empty
+          ~f:(fun ~key:_ ~data:subacc comm_bal_sums ->
+            let module Visitor = Account_structure.Basic_visitor (Structure) in
+            add_balance_maps comm_bal_sums
+              (Visitor.visit { car = collect_balances } subacc))
+
+  type delete_error = Not_found | Nonzero_balance
+
+  (*
   let rec delete_aux : type a. (Account_path.t * a f account) -> (a f account, delete_error) result = function
     | [], (extra, Leaf (_acc_comm, acc_bal)) ->
        if Money.Diff.(acc_bal = ~$0) then 
@@ -528,152 +534,152 @@ module Account_structure0 = struct
   let delete (aid : Account_path.t) (w : world) =
    *)
 
-    let world_inst : world =
-      String.Map.of_alist_exn
-        [
-          ( "Assets",
-            Structure.Asset
-              ( { description = "assets" },
-                Ind
-                  (String.Map.of_alist_exn
-                     [
-                       ( "Current",
-                         ( { description = "current" },
-                           Node
-                             (String.Map.of_alist_exn
-                                [
-                                  ( "Checking",
-                                    Structure.Bank
-                                      ( { description = "bnak accounts" },
-                                        Ind
-                                          (String.Map.of_alist_exn
-                                             [
-                                               ( "ING",
-                                                 ( { description = "ING bank" },
-                                                   Leaf ("EUC", Money.Diff.(~$0))
-                                                 ) );
-                                               ( "N26",
-                                                 ( { description = "ING bank" },
-                                                   Leaf ("EUC", Money.Diff.(~$0))
-                                                 ) );
-                                             ]) ) );
-                                ]) ) );
-                     ]) ) );
-        ]
-  end
-
-  module Bal_assert = struct
-    type t = { account : Account_path.t; labels : Labels.t; bal : Money.Diff.t }
-    [@@deriving sexp_of]
-  end
-
-  module Account_decl = struct
-    type t = {
-      type_ : Account_type.t0;
-      parent : Account_path.t;
-      name : string;
-      commodity : Commodity_id.t;
-      extra : Account_hierarchy.extra;
-    }
-    [@@deriving sexp_of]
-  end
-
-  module Tx : sig
-    type entry = {
-      dc : Debit_credit.t;
-      commodity : Commodity_id.t;
-      amount : Money.Amount.t;
-      assertion : Money.Diff.t option;
-    }
-
-    (* Private because we only want to allow constructing balanced transactions. *)
-    type t = private {
-      cleared : Date.t option;
-      entries : entry Account_path.Map.t;
-      labels : Labels.t;
-    }
+  let world_inst : world =
+    String.Map.of_alist_exn
+      [
+        ( "Assets",
+          Structure.Asset
+            ( { description = "assets" },
+              Ind
+                (String.Map.of_alist_exn
+                   [
+                     ( "Current",
+                       ( { description = "current" },
+                         Node
+                           (String.Map.of_alist_exn
+                              [
+                                ( "Checking",
+                                  Structure.Bank
+                                    ( { description = "bnak accounts" },
+                                      Ind
+                                        (String.Map.of_alist_exn
+                                           [
+                                             ( "ING",
+                                               ( { description = "ING bank" },
+                                                 Leaf ("EUC", Money.Diff.(~$0))
+                                               ) );
+                                             ( "N26",
+                                               ( { description = "ING bank" },
+                                                 Leaf ("EUC", Money.Diff.(~$0))
+                                               ) );
+                                           ]) ) );
+                              ]) ) );
+                   ]) ) );
+      ]
+end
 
-    type error = Unbalanced
+module Bal_assert = struct
+  type t = { account : Account_path.t; labels : Labels.t; bal : Money.Diff.t }
+  [@@deriving sexp_of]
+end
 
-    val make :
-      cleared:Date.t option ->
-      entries:entry Account_path.Map.t ->
-      labels:Labels.t ->
-      (t, error) result
+module Account_decl = struct
+  type t = {
+    type_ : Account_type.t0;
+    parent : Account_path.t;
+    name : string;
+    commodity : Commodity_id.t;
+    extra : Account_hierarchy.extra;
+  }
+  [@@deriving sexp_of]
+end
 
-    val sexp_of_t : t -> Sexp.t
-  end = struct
-    type entry = {
-      dc : Debit_credit.t;
-      commodity : Commodity_id.t;
-      amount : Money.Amount.t;
-      assertion : Money.Diff.t option;
-    }
-    [@@deriving sexp_of]
+module Tx : sig
+  type entry = {
+    dc : Debit_credit.t;
+    commodity : Commodity_id.t;
+    amount : Money.Amount.t;
+    assertion : Money.Diff.t option;
+  }
+
+  (* Private because we only want to allow constructing balanced transactions. *)
+  type t = private {
+    cleared : Date.t option;
+    entries : entry Account_path.Map.t;
+    labels : Labels.t;
+  }
+
+  type error = Unbalanced
+
+  val make :
+    cleared:Date.t option ->
+    entries:entry Account_path.Map.t ->
+    labels:Labels.t ->
+    (t, error) result
+
+  val sexp_of_t : t -> Sexp.t
+end = struct
+  type entry = {
+    dc : Debit_credit.t;
+    commodity : Commodity_id.t;
+    amount : Money.Amount.t;
+    assertion : Money.Diff.t option;
+  }
+  [@@deriving sexp_of]
 
-    type t = {
-      cleared : Date.t option;
-      entries : entry Account_path.Map.t;
-      labels : Labels.t;
-    }
-    [@@deriving sexp_of]
+  type t = {
+    cleared : Date.t option;
+    entries : entry Account_path.Map.t;
+    labels : Labels.t;
+  }
+  [@@deriving sexp_of]
 
-    type error = Unbalanced
-
-    let is_balanced entries =
-      Map.fold entries ~init:Commodity_id.Map.empty
-        ~f:(fun ~key:_ ~data comm_balances ->
-          Map.update comm_balances data.commodity ~f:(fun ocomm_bal ->
-              let comm_bal = Option.value ocomm_bal ~default:Money.Diff.(~$0) in
-              match data.dc with
-              | Debit_credit.Debit -> Money.Diff.(comm_bal +% data.amount)
-              | Debit_credit.Credit -> Money.Diff.(comm_bal -% data.amount)))
-      |> Map.for_all ~f:(fun comm_bal -> Money.Diff.(comm_bal = ~$0))
-
-    let make ~cleared ~entries ~labels =
-      if not (is_balanced entries) then Error Unbalanced
-      else Ok { cleared; entries; labels }
-  end
+  type error = Unbalanced
+
+  let is_balanced entries =
+    Map.fold entries ~init:Commodity_id.Map.empty
+      ~f:(fun ~key:_ ~data comm_balances ->
+        Map.update comm_balances data.commodity ~f:(fun ocomm_bal ->
+            let comm_bal = Option.value ocomm_bal ~default:Money.Diff.(~$0) in
+            match data.dc with
+            | Debit_credit.Debit -> Money.Diff.(comm_bal +% data.amount)
+            | Debit_credit.Credit -> Money.Diff.(comm_bal -% data.amount)))
+    |> Map.for_all ~f:(fun comm_bal -> Money.Diff.(comm_bal = ~$0))
+
+  let make ~cleared ~entries ~labels =
+    if not (is_balanced entries) then Error Unbalanced
+    else Ok { cleared; entries; labels }
+end
 
-  type item =
-    | Tx_item of Tx.t
-    | Bal_assert_item of Bal_assert.t
-    | Account_decl_item of Account_decl.t
-  [@@deriving sexp_of]
+type item =
+  | Tx_item of Tx.t
+  | Bal_assert_item of Bal_assert.t
+  | Account_decl_item of Account_decl.t
+[@@deriving sexp_of]
 
-  type t = item list [@@deriving sexp_of]
+type t = item list [@@deriving sexp_of]
 
-  module World = struct
-    type t = Account_hierarchy.world
+module World = struct
+  type t = Account_hierarchy.world
 
-    let empty : t = String.Map.empty
+  let empty : t = String.Map.empty
 
-    let apply_tx (tx : Tx.t) world : t option =
-      Map.fold_option tx.entries ~init:world
-        ~f:(fun ~key:aid ~(data : Tx.entry) world ->
-          let open Option.Let_syntax in
-          let%bind _old_bal, new_bal, world =
-            Account_hierarchy.update_bal aid data.dc data.amount data.commodity
-              world
-          in
-          match data.assertion with
-          | None -> Some world
-          | Some bal_ass ->
-              if Money.Diff.(bal_ass = new_bal) then Some world else None)
-
-    let apply_ba (ba : Bal_assert.t) world : t option =
-      let open Option.Let_syntax in
-      let%bind _comm, bal = Account_hierarchy.get_bal ba.account world in
-      if not Money.Diff.(bal = ba.bal) then None else Some world
-
-    let apply_ad (_ad : Account_decl.t) _world : t option = None
-
-    let apply : item -> t -> t option = function
-      | Tx_item tx -> apply_tx tx
-      | Bal_assert_item ba -> apply_ba ba
-      | Account_decl_item ad -> apply_ad ad
-  end
+  let apply_tx (tx : Tx.t) world : t option =
+    Map.fold_option tx.entries ~init:world
+      ~f:(fun ~key:aid ~(data : Tx.entry) world ->
+        let open Option.Let_syntax in
+        let%bind _old_bal, new_bal, world =
+          Account_hierarchy.update_bal aid data.dc data.amount data.commodity
+            world
+        in
+        match data.assertion with
+        | None -> Some world
+        | Some bal_ass ->
+            if Money.Diff.(bal_ass = new_bal) then Some world else None)
+
+  let apply_ba (ba : Bal_assert.t) world : t option =
+    let open Option.Let_syntax in
+    let%bind _comm, bal = Account_hierarchy.get_bal ba.account world in
+    if not Money.Diff.(bal = ba.bal) then None else Some world
+
+  let apply_ad (_ad : Account_decl.t) _world : t option = None
+
+  let apply : item -> t -> t option = function
+    | Tx_item tx -> apply_tx tx
+    | Bal_assert_item ba -> apply_ba ba
+    | Account_decl_item ad -> apply_ad ad
+end
 
-  module Ctxd_item = struct end
+module Ctxd_item = struct end
 
-  let make = Fn.id
+let make = Fn.id