Implement doomeer#26: set_aside multiple items in a list

* state.aside is now a list
* set_aside pushes the current item as the head
* with_aside fails if the list is empty; uses head otherwise
* awaken and recombine consume the head of the list
* beastcraft_split pushes the split item as the head of the list
* swap replaces the current item with the head of the list
  * if there is no current item: removes the head of the list, if not empty
  * if the list is empty: sets the current item to None

src/interpreter.ml

@@ -66,7 +66,7 @@ type state =
     echo: string -> unit;
     debug: string -> unit;
     item: Item.t option;
-    aside: Item.t option;
+    aside: Item.t list;
     imprint: Item.t option;
     paid: Amount.t;
     gained: Amount.t;
@@ -79,7 +79,7 @@ let start ~echo ~debug program =
     echo;
     debug;
     item = None;
-    aside = None;
+    aside = [];
     imprint = None;
     paid = Amount.zero;
     gained = Amount.zero;
@@ -96,9 +96,9 @@ let with_item state f =
 
 let with_aside state f =
   match state.aside with
-    | None ->
+    | [] ->
         fail "no item set aside"
-    | Some item ->
+    | item :: _ ->
         f item
 
 module Q:
@@ -554,13 +554,33 @@ let apply_currency state (currency: AST.currency) =
           |> Item.add_influence (SEC aside_influence)
           |> Item.spawn_additional_random_mods
         in
-        { (return item) with aside = None }
+        {
+          (return item) with
+            aside = match state.aside with
+              | [] -> [] (* cannot happen *)
+              | _ :: t -> t
+        }
     | Armour_recombinator ->
-        { (return @@ recombine state `armour) with aside = None }
+        {
+          (return @@ recombine state `armour) with
+            aside = match state.aside with
+              | [] -> [] (* cannot happen *)
+              | _ :: t -> t
+        }
     | Weapon_recombinator ->
-        { (return @@ recombine state `weapon) with aside = None }
+        {
+          (return @@ recombine state `weapon) with
+            aside = match state.aside with
+              | [] -> [] (* cannot happen *)
+              | _ :: t -> t
+        }
     | Jewellery_recombinator ->
-        { (return @@ recombine state `jewellery) with aside = None }
+        {
+          (return @@ recombine state `jewellery) with
+            aside = match state.aside with
+              | [] -> [] (* cannot happen *)
+              | _ :: t -> t
+        }
     | Ember tier ->
         with_item state @@ fun item ->
         return @@ Item.apply_eldritch_ember (AST.eldritch_tier_of_currency tier) item
@@ -655,7 +675,7 @@ let apply_currency state (currency: AST.currency) =
         );
         let item1, item2 = Item.split item in
         let state = return item1 in
-        { state with aside = Some item2 }
+        { state with aside = item2 :: state.aside }
     | Beastcraft_imprint ->
         with_item state @@ fun item ->
         item_must_be_normal_or_magic item;
@@ -771,10 +791,24 @@ let run_simple_instruction state (instruction: AST.simple_instruction) =
     | Set_aside ->
         state.debug "set aside";
         with_item state @@ fun item ->
-        goto_next { state with aside = Some item; item = None }
+        goto_next {
+          state with
+            aside = item :: state.aside;
+            item = None
+        }
     | Swap ->
         state.debug "swap";
-        goto_next { state with aside = state.item; item = state.aside }
+        let aside = match state.aside, state.item with
+          | [], None -> []
+          | [], Some item -> [item]
+          | h :: t, None -> t
+          | h :: t, Some item -> item :: t
+        in
+        let item = match state.aside with
+          | [] -> None
+          | h :: t -> Some h
+        in
+        goto_next { state with aside; item }
     | Use_imprint ->
         state.debug "use_imprint";
         let imprint =