diff --git a/stdlib/Makefile b/stdlib/Makefile
index ffe1b8fbcd8..bc653692c98 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -44,6 +44,7 @@ docMd: \
 	$(DOCDIR)/README.md \
 	$(DOCDIR)/prelude.md \
 	$(DOCDIR)/option.md \
+	$(DOCDIR)/result.md \
 	$(DOCDIR)/hash.md \
 	$(DOCDIR)/list.md \
 	$(DOCDIR)/assocList.md \
@@ -66,6 +67,7 @@ docHtml: \
 	$(DOCDIR)/README.html \
 	$(DOCDIR)/prelude.html \
 	$(DOCDIR)/option.html \
+	$(DOCDIR)/result.html \
 	$(DOCDIR)/hash.html \
 	$(DOCDIR)/list.html \
 	$(DOCDIR)/assocList.html \
@@ -133,7 +135,7 @@ $(OUTDIR)/SetDbTest.out: prelude.as hash.as list.as assocList.as trie.as set.as
 	$(ASC) -r $(filter-out $(OUTDIR), $^) > $@
 
 PRODUCE_EXCHANGE_SRC=\
-	prelude.as option.as hash.as list.as assocList.as trie.as docTable.as \
+	prelude.as option.as hash.as list.as assocList.as trie.as docTable.as result.as \
 	examples/produce-exchange/serverTypes.as \
 	examples/produce-exchange/serverModelTypes.as \
 	examples/produce-exchange/serverModel.as \
@@ -141,7 +143,7 @@ PRODUCE_EXCHANGE_SRC=\
 
 $(OUTDIR)/ProduceExchange.out: $(PRODUCE_EXCHANGE_SRC) \
 	examples/produce-exchange/test/simpleSetupAndQuery.as | $(OUTDIR)
-	$(ASC) -r $(filter-out $(OUTDIR), $^) > $@
+	$(ASC) -dt -r $(filter-out $(OUTDIR), $^) > $@
 
 $(OUTDIR)/ProduceExchange.wasm: $(PRODUCE_EXCHANGE_SRC) | $(OUTDIR)
 	$(ASC) -c --dfinity -o $@ $(filter-out $(OUTDIR), $^)
diff --git a/stdlib/examples/produce-exchange/serverActor.as b/stdlib/examples/produce-exchange/serverActor.as
index ee3a519046e..a347f8bc5fa 100644
--- a/stdlib/examples/produce-exchange/serverActor.as
+++ b/stdlib/examples/produce-exchange/serverActor.as
@@ -64,16 +64,19 @@ actor server = {
     isProducer: Bool,
     isRetailer: Bool,
     isTransporter: Bool
-  ) : async ?UserId {
-    getModel().addUser(
-      public_key,
-      user_name,
-      description,
-      region,
-      isDeveloper,
-      isProducer,
-      isRetailer,
-      isTransporter
+  ) : async Result<UserId,IdErr> {
+    optionResult<UserId,IdErr>(
+      getModel().addUser(
+        public_key,
+        user_name,
+        description,
+        region,
+        isDeveloper,
+        isProducer,
+        isRetailer,
+        isTransporter
+      ),
+      {#idErr}
     )
   };
 
@@ -91,9 +94,11 @@ actor server = {
    ---------------------------
    Get the information associated with a user, based on its id.
    */
-  getUserInfo(id:UserId) : async ?UserInfo {
-    getModel()
-      .userTable.getInfo(id)
+  getUserInfo(id:UserId) : async Result<UserInfo, IdErr> {
+    optionResult<UserInfo, IdErr>(
+      getModel().userTable.getInfo(id),
+      {#idErr}
+    )
   };
 
  /**
@@ -115,26 +120,28 @@ actor server = {
     capacity_ : Weight,
     isFridge_ : Bool,
     isFreezer_ : Bool,
-  ) : async ?TruckTypeId {
-    getModel()
-      .truckTypeTable.addInfoGetId(
+  ) : async Result<TruckTypeId,None> {
+    optionUnwrapResult<TruckTypeId>(
+      getModel()
+        .truckTypeTable.addInfoGetId(
         func (id_:TruckTypeId) : TruckTypeInfo =
 
-        // xxx: AS should have more concise syntax for this pattern, below:
-        // two problems I see, that are separate:
-        // 1: repeating the label/variable name, which is the same in each case, twice.
-        // 2: explicit type annotations, because of "type error, cannot infer type of forward variable ..."
-        //    but two other sources exist for each type: the type of `insert` is known, and hence, this record has a known type,
-        //    and, the type of each of these `variables` is known, as well.
-
-        shared {
-          id=id_ :TruckTypeId;
-          short_name=short_name_:Text;
-          description=description_:Text;
-          capacity=capacity_:Weight;
-          isFridge=isFridge_:Bool;
-          isFreezer=isFreezer_:Bool;
-        })
+          // xxx: AS should have more concise syntax for this pattern, below:
+          // two problems I see, that are separate:
+          // 1: repeating the label/variable name, which is the same in each case, twice.
+          // 2: explicit type annotations, because of "type error, cannot infer type of forward variable ..."
+          //    but two other sources exist for each type: the type of `insert` is known, and hence, this record has a known type,
+          //    and, the type of each of these `variables` is known, as well.
+
+          shared {
+            id=id_ :TruckTypeId;
+            short_name=short_name_:Text;
+            description=description_:Text;
+            capacity=capacity_:Weight;
+            isFridge=isFridge_:Bool;
+            isFreezer=isFreezer_:Bool;
+          })
+    )
   };
 
   /**
@@ -144,8 +151,11 @@ actor server = {
 
   registrarRemTruckType(
     id: TruckTypeId
-  ) : async ?() {
-    getModel().truckTypeTable.remGetUnit(id)
+  ) : async Result<(),ServerErr> {
+    optionResult<(),IdErr>(
+      getModel().truckTypeTable.remGetUnit(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -155,8 +165,11 @@ actor server = {
 
   getTruckTypeInfo(
     id: TruckTypeId
-  ) : async ?TruckTypeInfo {
-    getModel().truckTypeTable.getInfo(id)
+  ) : async Result<TruckTypeInfo,IdErr> {
+    optionResult<TruckTypeInfo,IdErr>(
+      getModel().truckTypeTable.getInfo(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -186,14 +199,16 @@ actor server = {
   registrarAddRegion(
     short_name_:  Text,
     description_: Text,
-  ) : async ?RegionId {
-    getModel().regionTable.addInfoGetId(
-      func (id_:RegionId) : RegionInfo =
-        shared {
-          id = id_:RegionId;
-          short_name=short_name_:Text;
-          description=description_:Text
-        })
+  ) : async Result<RegionId,None> {
+    optionUnwrapResult<RegionId>(
+      getModel().regionTable.addInfoGetId(
+        func (id_:RegionId) : RegionInfo =
+          shared {
+            id = id_:RegionId;
+            short_name=short_name_:Text;
+            description=description_:Text
+          })
+    )
   };
 
   /**
@@ -205,8 +220,11 @@ actor server = {
 
   registrarRemRegion(
     id: RegionId
-  ) : async ?() {
-    getModel().regionTable.remGetUnit(id)
+  ) : async Result<(),IdErr> {
+    optionResult<(),IdErr>(
+      getModel().regionTable.remGetUnit(id),
+      {#idErr},
+    )
   };
 
   /**
@@ -219,8 +237,11 @@ actor server = {
 
   getRegionInfo(
     id: RegionId
-  ) : async ?RegionInfo {
-    getModel().regionTable.getInfo(id)
+  ) : async Result<RegionInfo,IdErr> {
+    optionResult<RegionInfo,IdErr>(
+      getModel().regionTable.getInfo(id),
+      {#idErr}
+    )
   };
 
 
@@ -255,15 +276,17 @@ actor server = {
     short_name_:  Text,
     description_: Text,
     grade_: Grade,
-  ) : async ?ProduceId {
-    getModel().produceTable.addInfoGetId(
-      func (id_:ProduceId) : ProduceInfo =
-        shared {
-          id = id_:ProduceId;
-          short_name=short_name_:Text;
-          description=description_:Text;
-          grade=grade_:Grade
-        })
+  ) : async Result<ProduceId,None> {
+    optionUnwrapResult<ProduceId>(
+      getModel().produceTable.addInfoGetId(
+        func (id_:ProduceId) : ProduceInfo =
+          shared {
+            id = id_:ProduceId;
+            short_name=short_name_:Text;
+            description=description_:Text;
+            grade=grade_:Grade
+          })
+    )
   };
 
   /**
@@ -275,8 +298,11 @@ actor server = {
 
   registrarRemProduce(
     id: ProduceId
-  ) : async ?() {
-    getModel().produceTable.remGetUnit(id)
+  ) : async Result<(),IdErr> {
+    optionResult<(),IdErr>(
+      getModel().produceTable.remGetUnit(id),
+      {#idErr},
+    )
   };
 
 
@@ -287,8 +313,11 @@ actor server = {
 
   getProduceInfo(
     id: ProduceId
-  ) : async ?ProduceInfo {
-    getModel().produceTable.getInfo(id)
+  ) : async Result<ProduceInfo,IdErr> {
+    optionResult<ProduceInfo,IdErr>(
+      getModel().produceTable.getInfo(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -318,18 +347,21 @@ actor server = {
     short_name_:  Text,
     description_: Text,
     region_: RegionId,
-  ) : async ?ProducerId {
-    getModel().producerTable.addInfoGetId(
-      func(id_:ProducerId):ProducerInfo {
-        shared {
-          id=id_:ProducerId;
-          short_name=short_name_:Text;
-          description=description_:Text;
-          region=region_:RegionId;
-          inventory=[];
-          reserved=[];
-        }
-      })
+  ) : async Result<ProducerId,IdErr> {
+    optionResult<ProduceId,IdErr>(
+      getModel().producerTable.addInfoGetId(
+        func(id_:ProducerId):ProducerInfo {
+          shared {
+            id=id_:ProducerId;
+            short_name=short_name_:Text;
+            description=description_:Text;
+            region=region_:RegionId;
+            inventory=[];
+            reserved=[];
+          }
+        }),
+      {#idErr}
+    )
   };
 
   /**
@@ -341,8 +373,11 @@ actor server = {
 
   registrarRemProducer(
     id: ProducerId
-  ) : async ?() {
-    getModel().producerTable.remGetUnit(id)
+  ) : async Result<(),IdErr> {
+    optionResult<(),IdErr>(
+      getModel().producerTable.remGetUnit(id),
+      {#idErr}
+    )
   };
 
 
@@ -353,8 +388,11 @@ actor server = {
 
   getProducerInfo(
     id: ProducerId
-  ) : async ?ProducerInfo {
-    getModel().producerTable.getInfo(id)
+  ) : async Result<ProducerInfo,IdErr> {
+    optionResult<ProducerInfo,IdErr>(
+      getModel().producerTable.getInfo(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -385,16 +423,19 @@ actor server = {
     short_name_:  Text,
     description_: Text,
     region_: RegionId,
-  ) : async ?RetailerId {
-    getModel().retailerTable.addInfoGetId(
-      func(id_:RetailerId):RetailerInfo {
-        shared {
-          id=id_:RetailerId;
-          short_name=short_name_:Text;
-          description=description_:Text;
-          region=region_:RegionId
-        }
-      })
+  ) : async Result<RetailerId,IdErr> {
+    optionResult<RetailerId,IdErr>(
+      getModel().retailerTable.addInfoGetId(
+        func(id_:RetailerId):RetailerInfo {
+          shared {
+            id=id_:RetailerId;
+            short_name=short_name_:Text;
+            description=description_:Text;
+            region=region_:RegionId
+          }
+        }),
+      {#idErr}
+    )
   };
 
   /**
@@ -406,8 +447,11 @@ actor server = {
 
   registrarRemRetailer(
     id: RetailerId
-  ) : async ?() {
-    getModel().retailerTable.remGetUnit(id)
+  ) : async Result<(),IdErr> {
+    optionResult<(),IdErr>(
+      getModel().retailerTable.remGetUnit(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -417,8 +461,11 @@ actor server = {
 
   getRetailerInfo(
     id: RetailerId
-  ) : async ?RetailerInfo {
-    getModel().retailerTable.getInfo(id)
+  ) : async Result<RetailerInfo,IdErr> {
+    optionResult<RetailerInfo,IdErr>(
+      getModel().retailerTable.getInfo(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -445,18 +492,19 @@ actor server = {
   registrarAddTransporter(
     short_name_:  Text,
     description_: Text,
-  ) : async ?TransporterId {
-    getModel().transporterTable.addInfoGetId(
-      func(id_:TransporterId):TransporterInfo {
-        shared {
-          id=id_:TransporterId;
-          short_name=short_name_:Text;
-          description=description_:Text;
-          routes=[];
-          reserved=[];
-        }
-      })
-
+  ) : async Result<TransporterId,None> {
+    optionUnwrapResult<TransporterId>(
+      getModel().transporterTable.addInfoGetId(
+        func(id_:TransporterId):TransporterInfo {
+          shared {
+            id=id_:TransporterId;
+            short_name=short_name_:Text;
+            description=description_:Text;
+            routes=[];
+            reserved=[];
+          }
+        })
+    )
   };
 
   /**
@@ -467,8 +515,11 @@ actor server = {
 
   registrarRemTransporter(
     id: TransporterId
-  ) : async ?() {
-    getModel().transporterTable.remGetUnit(id)
+  ) : async Result<(),IdErr> {
+    optionResult<(),IdErr>(
+      getModel().transporterTable.remGetUnit(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -478,8 +529,11 @@ actor server = {
 
   getTransporterInfo(
     id: TransporterId
-  ) : async ?TransporterInfo {
-    getModel().transporterTable.getInfo(id)
+  ) : async Result<TransporterInfo,IdErr> {
+    optionResult<TransporterInfo,IdErr>(
+      getModel().transporterTable.getInfo(id),
+      {#idErr}
+    )
   };
 
 
@@ -514,7 +568,7 @@ actor server = {
     begin:Date,
     end:  Date,
     comments: Text,
-  ) : async ?InventoryId {
+  ) : async Result<InventoryId,ServerErr> {
     getModel().
       producerAddInventory(
         public_key, null, id, prod, quant, weight, ppu, begin, end, comments)
@@ -536,7 +590,7 @@ actor server = {
     begin:Date,
     end:  Date,
     comments: Text,
-  ) : async ?() {
+  ) : async Result<(),ServerErr> {
     getModel().
       producerUpdateInventory(
         public_key, iid, id, prod, quant, weight, ppu, begin, end, comments)
@@ -546,7 +600,7 @@ actor server = {
    `producerRemInventory`
    ---------------------------
    */
-  producerRemInventory(public_key: PublicKey, id:InventoryId) : async ?() {
+  producerRemInventory(public_key: PublicKey, id:InventoryId) : async Result<(),ServerErr> {
     getModel()
       .producerRemInventory(public_key, id)
   };
@@ -555,18 +609,24 @@ actor server = {
    `producerAllInventoryInfo`
    ---------------------------
    */
-  producerAllInventoryInfo(public_key: PublicKey, id:UserId) : async ?[InventoryInfo] {
-    getModel()
-      .producerAllInventoryInfo(public_key, id)
+  producerAllInventoryInfo(public_key: PublicKey, id:UserId) : async Result<[InventoryInfo],IdErr> {
+    optionResult<[InventoryInfo],IdErr>(
+      getModel()
+        .producerAllInventoryInfo(public_key, id),
+      {#idErr}
+    )
   };
 
   /**
    `producerReservations`
    ---------------------------
    */
-  producerReservations(public_key: PublicKey, id:UserId) : async ?[ReservedInventoryInfo] {
-    getModel()
-      .producerReservations(public_key, id)
+  producerReservations(public_key: PublicKey, id:UserId) : async Result<[ReservedInventoryInfo],IdErr> {
+    optionResult<[ReservedInventoryInfo],IdErr>(
+      getModel()
+        .producerReservations(public_key, id),
+      {#idErr}
+    )
   };
 
 
@@ -582,9 +642,12 @@ actor server = {
    ---------------------------
    The last sales price for produce within a given geographic area; null region id means "all areas."
    */
-  produceMarketInfo(public_key: PublicKey, id:ProduceId, reg:?RegionId) : async ?[ProduceMarketInfo] {
-    getModel()
-      .produceMarketInfo(public_key, id, reg)
+  produceMarketInfo(public_key: PublicKey, id:ProduceId, reg:?RegionId) : async Result<[ProduceMarketInfo],IdErr> {
+    optionResult<[ProduceMarketInfo],IdErr>(
+      getModel()
+        .produceMarketInfo(public_key, id, reg),
+      {#idErr}
+    )
   };
 
 
@@ -603,9 +666,12 @@ actor server = {
    ---------------------------
    Get the information associated with inventory, based on its id.
    */
-  getInventoryInfo(id:InventoryId) : async ?InventoryInfo {
-    getModel()
-      .inventoryTable.getInfo(id)
+  getInventoryInfo(id:InventoryId) : async Result<InventoryInfo,IdErr> {
+    optionResult<InventoryInfo,IdErr>(
+      getModel()
+        .inventoryTable.getInfo(id),
+      {#idErr}
+    )
   };
 
 
@@ -627,7 +693,7 @@ actor server = {
     end:    Date,
     cost:   Price,
     ttid:   TruckTypeId
-  ) : async ?RouteId {
+  ) : async Result<RouteId,ServerErr> {
     getModel().transporterAddRoute(public_key, null, id, rstart, rend, start, end, cost, ttid)
   };
 
@@ -645,7 +711,7 @@ actor server = {
     end:    Date,
     cost:   Price,
     ttid:   TruckTypeId
-  ) : async ?() {
+  ) : async Result<(),ServerErr> {
     getModel().transporterUpdateRoute(public_key, route, id, rstart, rend, start, end, cost, ttid)
   };
 
@@ -653,27 +719,33 @@ actor server = {
    `transporterRemRoute`
    ---------------------------
    */
-  transporterRemRoute(public_key: PublicKey, id:RouteId) : async ?() {
-    getModel()
-      .transporterRemRoute(public_key, id)
+  transporterRemRoute(public_key: PublicKey, id:RouteId) : async Result<(),ServerErr> {
+      getModel()
+        .transporterRemRoute(public_key, id)
   };
 
   /**
    `transporterAllRouteInfo`
    ---------------------------
    */
-  transporterAllRouteInfo(public_key: PublicKey, id:UserId) : async ?[RouteInfo] {
-    getModel()
-      .transporterAllRouteInfo(public_key, id)
+  transporterAllRouteInfo(public_key: PublicKey, id:UserId) : async Result<[RouteInfo],IdErr> {
+    optionResult<[RouteInfo],IdErr>(
+      getModel()
+        .transporterAllRouteInfo(public_key, id),
+      {#idErr}
+    )
   };
 
   /**
    `transporterAllReservationInfo`
    ---------------------------
    */
-  transporterAllReservationInfo(public_key: PublicKey, id:UserId) : async ?[ReservedRouteInfo] {
-    getModel()
-      .transporterAllReservationInfo(public_key, id)
+  transporterAllReservationInfo(public_key: PublicKey, id:UserId) : async Result<[ReservedRouteInfo],IdErr> {
+    optionResult<[ReservedRouteInfo],IdErr>(
+      getModel()
+        .transporterAllReservationInfo(public_key, id),
+      {#idErr}
+    )
   };
 
   /**
@@ -696,8 +768,11 @@ actor server = {
 
   getRouteInfo(
     id: RouteId
-  ) : async ?RouteInfo {
-    getModel().routeTable.getInfo(id)
+  ) : async Result<RouteInfo,IdErr> {
+    optionResult<RouteInfo,IdErr>(
+      getModel().routeTable.getInfo(id),
+      {#idErr}
+    )
   };
 
   /**
@@ -707,12 +782,16 @@ actor server = {
    `retailerQueryAll`
    ---------------------------
 
-   TODO-Cursors (see above).
-
    */
-  retailerQueryAll(public_key: PublicKey, id:UserId) : async ?QueryAllResults {
-    getModel().
-      retailerQueryAll(public_key, id)
+  retailerQueryAll(public_key: PublicKey, id:UserId,
+                   queryProduce:?ProduceId,
+                   queryDate:?Date
+  ) : async Result<QueryAllResults,IdErr> {
+    optionResult<QueryAllResults,IdErr>(
+      getModel().
+        retailerQueryAll(public_key, id, queryProduce, queryDate),
+      {#idErr}
+    )
   };
 
   /**
@@ -729,10 +808,13 @@ actor server = {
     id:UserId,
     begin:Date,
     end:Date
-  ) : async ?[InventoryInfo]
+  ) : async Result<[InventoryInfo],IdErr>
   {
-    getModel().
-      retailerQueryDates(public_key, id, begin, end)
+    optionResult<[InventoryInfo],IdErr>(
+      getModel().
+        retailerQueryDates(public_key, id, begin, end),
+      {#idErr}
+    )
   };
 
   /**
@@ -743,7 +825,7 @@ actor server = {
     public_key: PublicKey,
     id:UserId,
     inventory:InventoryId,
-    route:RouteId) : async ?(ReservedInventoryId, ReservedRouteId)
+    route:RouteId) : async Result<(ReservedInventoryId, ReservedRouteId),ServerErr>
   {
     getModel().
       retailerReserve(public_key, id, inventory, route)
@@ -753,15 +835,17 @@ actor server = {
    `retailerReservations`
    ---------------------------
 
-   TODO-Cursors (see above).
-
-   */
+  */
   retailerReservations(public_key: PublicKey, id:UserId) :
-    async ?[(ReservedInventoryInfo,
-             ReservedRouteInfo)]
+    async Result<[(ReservedInventoryInfo,
+                   ReservedRouteInfo)],ServerErr>
   {
-    getModel().
-      retailerAllReservationInfo(public_key, id)
+    optionResult<[(ReservedInventoryInfo,
+                   ReservedRouteInfo)],ServerErr>(
+      getModel().
+        retailerAllReservationInfo(public_key, id),
+      #idErr
+    )
   };
 
 
diff --git a/stdlib/examples/produce-exchange/serverModel.as b/stdlib/examples/produce-exchange/serverModel.as
index d368524d1e2..d507bec9aae 100644
--- a/stdlib/examples/produce-exchange/serverModel.as
+++ b/stdlib/examples/produce-exchange/serverModel.as
@@ -766,8 +766,6 @@ than the MVP goals, however.
       case (?doc) { doc };
     };
 
-    assert(isValidUser(public_key, doc.short_name));
-
     ?Map.toArray<InventoryId,InventoryDoc,InventoryInfo>(
       doc.inventory,
       func (_:InventoryId,doc:InventoryDoc):[InventoryInfo] =
@@ -791,7 +789,7 @@ than the MVP goals, however.
     start_date_: Date,
     end_date_  : Date,
     comments_  : Text,
-  ) : ?InventoryId
+  ) : Result<InventoryId, ServerErr>
   {
     /** The model adds inventory and maintains secondary indicies as follows: */
 
@@ -801,10 +799,12 @@ than the MVP goals, however.
     let (producer_, produce_) = {
       switch (oproducer, oproduce) {
       case (?producer, ?produce) (producer, produce);
-      case _ { return null };
+      case _ { return #err(#idErr) };
       }};
 
-    assert(isValidUser(public_key, producer_.short_name));
+    if (not isValidUser(public_key, producer_.short_name)) {
+      return (#err(#publicKeyErr))
+    };
 
     /**- Create the inventory item document: */
     let (_, item) = {
@@ -857,7 +857,7 @@ than the MVP goals, however.
       updatedInventory,
     );
 
-    ?item.id
+    return #ok(item.id)
   };
 
   /**
@@ -876,7 +876,7 @@ than the MVP goals, however.
     start_date_: Date,
     end_date_  : Date,
     comments_  : Text,
-  ) : ?()
+  ) : Result<(),ServerErr>
   {
     /**- Validate these ids; fail here if anything is invalid: */
     let oproducer: ?ProducerDoc = producerFromUserId(id_);
@@ -891,19 +891,21 @@ than the MVP goals, however.
              if ( inventory.producer == producer.id ) {
                (inventory, producer, produce)
              } else {
-               return null
+               return (#err(#idErr))
              }
            };
-      case _ { return null };
+      case _ { return (#err(#idErr)) };
       }};
 
-    assert(isValidUser(public_key, producer_.short_name));
+    if (not isValidUser(public_key, producer_.short_name)) {
+      return (#err(#publicKeyErr))
+    };
 
     /**- remove the inventory item; given the validation above, this cannot fail. */
-    assertSome<()>( producerRemInventory(public_key, iid_) );
+    assertOk( producerRemInventory(public_key, iid_) );
 
     /**- add the (updated) inventory item; given the validation above, this cannot fail. */
-    assertSome<InventoryId>(
+    assertOk(
       producerAddInventory(
         public_key, ?iid_, id_,
         produce_id,
@@ -911,7 +913,7 @@ than the MVP goals, however.
     );
 
     /**- Success! */
-    ?()
+    #ok
   };
 
   /**
@@ -921,12 +923,12 @@ than the MVP goals, however.
    Remove the given inventory item from the exchange.
 
    */
-  producerRemInventory(public_key: PublicKey, id:InventoryId) : ?() {
+  producerRemInventory(public_key: PublicKey, id:InventoryId) : Result<(),ServerErr> {
 
     /**- validate the `id` */
     /// xxx macro for this pattern?
     let doc = switch (inventoryTable.getDoc(id)) {
-      case null { return null };
+      case null { return #err(#idErr) };
       case (?doc) { doc };
     };
 
@@ -934,7 +936,9 @@ than the MVP goals, however.
     let producer = unwrap<ProducerDoc>(producerTable.getDoc(doc.producer));
 
     /// xxx: access control: Check that the current user is the owner of this inventory
-    assert(isValidUser(public_key, producer.short_name));
+    if (not isValidUser(public_key, producer.short_name)) {
+      return (#err(#publicKeyErr))
+    };
 
     /**- remove document from `inventoryTable` */
     assertSome<InventoryDoc>(
@@ -973,7 +977,7 @@ than the MVP goals, however.
       t
     };
 
-    ?()
+    #ok
   };
 
   /**
@@ -987,8 +991,6 @@ than the MVP goals, however.
       case (?doc) { doc };
     };
 
-    assert(isValidUser(public_key, doc.short_name));
-
     ?Map.toArray<ReservedInventoryId,
                  ReservedInventoryDoc,
                  ReservedInventoryInfo>(
@@ -1022,7 +1024,7 @@ than the MVP goals, however.
     end_date_:       Date,
     cost_:           Price,
     trucktype_id:    TruckTypeId
-  ) : ?RouteId {
+  ) : Result<RouteId,ServerErr> {
     /** The model adds inventory and maintains secondary indicies as follows: */
 
     /**- Validate these ids; fail fast if not defined: */
@@ -1033,11 +1035,13 @@ than the MVP goals, however.
     let (transporter, start_region_, end_region_, truck_type_) = {
       switch (otransporter, orstart, orend, otrucktype) {
       case (?x1, ?x2, ?x3, ?x4) (x1, x2, x3, x4);
-      case _ { return null };
+      case _ { return #err(#idErr) };
       }};
     let transporterId = transporter.id;
 
-    assert(isValidUser(public_key, transporter.short_name));
+    if (not isValidUser(public_key, transporter.short_name)) {
+      return (#err(#publicKeyErr))
+    };
 
     /**- Create the route item document: */
     let route : RouteDoc = {
@@ -1088,7 +1092,7 @@ than the MVP goals, however.
       route
     );
 
-    ?route.id
+    #ok(route.id)
   };
 
   /**
@@ -1106,7 +1110,7 @@ than the MVP goals, however.
     end_date_       : Date,
     cost_           : Price,
     trucktype_id    : TruckTypeId
-  ) : ?() {
+  ) : Result<(),ServerErr> {
     /** The model updates routes and maintains secondary indicies as follows: */
 
     /**- Validate these ids; fail fast if not defined: */
@@ -1124,19 +1128,22 @@ than the MVP goals, however.
              if ( route.transporter == transporter.id ) {
                (route, transporter, x2, x3, x4);
              } else {
-               return null
+               return #err(#idErr)
              }
            };
-      case _ { return null };
+      case _ { return #err(#idErr) };
       }};
 
-    assert(isValidUser(public_key, transporter.short_name));
+    /**- validate the user */
+    if (not isValidUser(public_key, transporter.short_name)) {
+      return #err(#publicKeyErr)
+    }
 
     /**- remove the route; given the validation above, this cannot fail. */
-    assertSome<()>( transporterRemRoute(public_key, rid_) );
+    assertOk( transporterRemRoute(public_key, rid_) );
 
     /**- add the (updated) route; given the validation above, this cannot fail. */
-    assertSome<RouteId>(
+    assertOk(
       transporterAddRoute(
         public_key,
         ?rid_, id_,
@@ -1150,7 +1157,7 @@ than the MVP goals, however.
     );
 
     /**- Success! */
-    ?()
+    #ok
   };
 
   /**
@@ -1158,23 +1165,23 @@ than the MVP goals, however.
    ---------------------------
    Remove the given route from the exchange.
    */
-  transporterRemRoute(public_key: PublicKey, id:RouteId) : ?() {
+  transporterRemRoute(public_key: PublicKey, id:RouteId) : Result<(),ServerErr> {
 
     let doc = switch (routeTable.getDoc(id)) {
-      case null { return null };
+      case null { return #err(#idErr) };
       case (?doc) { doc };
     };
 
     let transporter = unwrap<TransporterDoc>(transporterTable.getDoc(doc.transporter));
 
-    assert(isValidUser(public_key, transporter.short_name));
+    if (not isValidUser(public_key, transporter.short_name)) {
+      return #err(#publicKeyErr)
+    }
 
     assertSome<RouteDoc>(
       routeTable.rem( id )
     );
 
-    /// xxx: access control: Check that the current user is the owner of this route
-
     let (updatedRoutes, _) =
       Trie.remove<RouteId, RouteDoc>(
         transporter.routes, keyOf(id), idIsEq);
@@ -1202,7 +1209,7 @@ than the MVP goals, however.
       t
     };
 
-    ?()
+    #ok
   };
 
   /**
@@ -1215,8 +1222,6 @@ than the MVP goals, however.
       case (?doc) { doc };
     };
 
-    assert(isValidUser(public_key, doc.short_name));
-
     ?Map.toArray<RouteId,
                  RouteDoc,
                  RouteInfo>(
@@ -1240,8 +1245,6 @@ than the MVP goals, however.
       case (?doc) { doc };
     };
 
-    assert(isValidUser(public_key, doc.short_name));
-
     ?Map.toArray<ReservedRouteId,
                  ReservedRouteDoc,
                  ReservedRouteInfo>(
@@ -1309,7 +1312,33 @@ than the MVP goals, however.
 
   */
 
-  isFeasibleReservation(retailer:RetailerDoc, item:InventoryDoc, route:RouteDoc) : Bool {
+  isFeasibleReservation(
+    retailer:RetailerDoc,
+    item:InventoryDoc,
+    route:RouteDoc,
+    queryProduce:?ProduceId,
+    queryDate:?Date)
+    : Bool
+  {
+
+    switch queryProduce {
+      case null { };
+      case (?qp) {
+             if (item.produce.id != qp) {
+               debugOff "nope: wrong produce kind\n";
+               return false
+             };
+           };
+    };
+    switch queryDate {
+      case null { };
+      case (?qd) {
+             if (route.end_date > qd ) {
+               debugOff "nope: route arrives too late\n";
+               return false
+             }
+           }
+    };
     /** - window start: check that the route begins after the inventory window begins */
     if (item.start_date > route.start_date) {
       debugOff "nope: item start after route start\n";
@@ -1348,7 +1377,13 @@ than the MVP goals, however.
    - [`Trie.prod`]($DOCURL/trie.md#prod): For the catesian product of routes and inventory.
    - [`Trie.mergeDisjoint2D`]($DOCURL/trie.md#mergeDisjoint2D): To flatten 2D mappings into 1D mappings.
   */
-  retailerQueryAll(public_key: PublicKey, id:UserId) : ?QueryAllResults {
+  retailerQueryAll(
+    public_key: PublicKey,
+    id:UserId,
+    queryProduce:?ProduceId,
+    queryDate:?Date
+  ) : ?QueryAllResults
+  {
     retailerQueryCount += 1;
 
     /** - Find the retailer's document: */
@@ -1357,8 +1392,6 @@ than the MVP goals, however.
       case (null) { return null };
       case (?x) { x }};
 
-    assert(isValidUser(public_key, retailer.short_name));
-
     debug "- user_name: ";
     debug (retailer.short_name);
     debug ", public_key: ";
@@ -1416,7 +1449,7 @@ than the MVP goals, however.
         {
           retailerQueryCost += 1;
           /** - Consider the constraints of the retailer-route-item combination: */
-          if (isFeasibleReservation(retailer, item, route)) {
+          if (isFeasibleReservation(retailer, item, route, queryProduce, queryDate)) {
             ?( keyOfIdPair(route_id, item_id),
                (route, item)
             )
@@ -1466,8 +1499,6 @@ than the MVP goals, however.
       case (?doc) { doc };
     };
 
-    assert(isValidUser(public_key, doc.short_name));
-
     ?Map.toArray<ReservedInventoryId,
                  (ReservedInventoryDoc,  ReservedRouteDoc),
                  (ReservedInventoryInfo, ReservedRouteInfo)>(
@@ -1521,7 +1552,7 @@ than the MVP goals, however.
     public_key: PublicKey,
     id:UserId,
     inventory:InventoryId,
-    route:RouteId) : ?(ReservedRouteId, ReservedInventoryId)
+    route:RouteId) : Result<(ReservedRouteId, ReservedInventoryId), ServerErr>
   {
     nyi()
   };
diff --git a/stdlib/examples/produce-exchange/serverTypes.as b/stdlib/examples/produce-exchange/serverTypes.as
index 740f9119e7c..013bba03763 100644
--- a/stdlib/examples/produce-exchange/serverTypes.as
+++ b/stdlib/examples/produce-exchange/serverTypes.as
@@ -78,6 +78,21 @@ type TransporterId = Nat;
 type RouteId       = Nat;
 type ReservedRouteId = Nat;
 
+/**
+ Errors
+ -----------
+*/
+
+type IdErr = {
+  #idErr;
+};
+
+type ServerErr = {
+  #idErr;
+  #publicKeyErr;
+};
+
+
 /**
 Public info associated with Ids
 =====================================
diff --git a/stdlib/examples/produce-exchange/test/simpleSetupAndQuery.as b/stdlib/examples/produce-exchange/test/simpleSetupAndQuery.as
index e92b6d2aa2d..c8be27550bf 100644
--- a/stdlib/examples/produce-exchange/test/simpleSetupAndQuery.as
+++ b/stdlib/examples/produce-exchange/test/simpleSetupAndQuery.as
@@ -52,11 +52,11 @@ actor class Test() = this {
       printEntityCount("Produce", (await s.getCounts()).produce_count);
 
       // register all users
-      let uida = await s.registrarAddUser(pka, "usera", "", unwrap<RegionId>rega, true, true, true, true);
-      let uidb = await s.registrarAddUser(pkb, "userb", "", unwrap<RegionId>regb, true, true, true, true);
-      let uidc = await s.registrarAddUser(pkc, "userc", "", unwrap<RegionId>regc, true, true, true, true);
-      let uidd = await s.registrarAddUser(pkd, "userd", "", unwrap<RegionId>regd, true, true, true, true);
-      let uide = await s.registrarAddUser(pke, "usere", "", unwrap<RegionId>rege, true, true, true, true);
+      let uida = await s.registrarAddUser(pka, "usera", "", assertUnwrapAny<RegionId>rega, true, true, true, true);
+      let uidb = await s.registrarAddUser(pkb, "userb", "", assertUnwrapAny<RegionId>regb, true, true, true, true);
+      let uidc = await s.registrarAddUser(pkc, "userc", "", assertUnwrapAny<RegionId>regc, true, true, true, true);
+      let uidd = await s.registrarAddUser(pkd, "userd", "", assertUnwrapAny<RegionId>regd, true, true, true, true);
+      let uide = await s.registrarAddUser(pke, "usere", "", assertUnwrapAny<RegionId>rege, true, true, true, true);
 
       printEntityCount("Producer", (await s.getCounts()).producer_count);
       printEntityCount("Transporter", (await s.getCounts()).transporter_count);
@@ -65,48 +65,48 @@ actor class Test() = this {
       // populate with inventory
       let praia = await s.producerAddInventory(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<ProduceId>(pea), 100, 100, 10, 0, 110, ""
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<ProduceId>(pea), 100, 100, 10, 0, 110, ""
       );
       let praib = await s.producerAddInventory(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<ProduceId>(peb), 200, 200, 10, 1, 111, ""
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<ProduceId>(peb), 200, 200, 10, 1, 111, ""
       );
       let praic = await s.producerAddInventory(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<ProduceId>(pec), 300, 300, 10, 2, 112, ""
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<ProduceId>(pec), 300, 300, 10, 2, 112, ""
       );
       let prbia = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 200, 200, 10, 4, 117, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(peb), 200, 200, 10, 4, 117, ""
       );
       let prbib = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 1500, 1600, 9, 2, 115, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(peb), 1500, 1600, 9, 2, 115, ""
       );
       let prbic = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(pec), 300, 300, 10, 2, 112, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(pec), 300, 300, 10, 2, 112, ""
       );
       let prcia = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 200, 200, 9, 4, 711, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(peb), 200, 200, 9, 4, 711, ""
       );
       let prdib = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 1500, 1500, 7, 2, 115, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(peb), 1500, 1500, 7, 2, 115, ""
       );
       let prdic = await s.producerAddInventory(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(pec), 300, 300, 6, 2, 112, ""
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<ProduceId>(pec), 300, 300, 6, 2, 112, ""
       );
 
       printEntityCount("Inventory@time1", (await s.getCounts()).inventory_count);
@@ -115,17 +115,15 @@ actor class Test() = this {
 
       /**- remove some of the inventory items added above */
 
-      let x = await s.producerRemInventory(pkb, unwrap<InventoryId>(prdib));
-      assertSome<()>(x);
+      assertOk(await s.producerRemInventory(pkb, assertUnwrapAny<InventoryId>(prdib)));
 
       // a double-remove should return null
-      assertNull<()>(await s.producerRemInventory(pkb, unwrap<InventoryId>(prdib)));
+      //assertErr(await s.producerRemInventory(pkb, assertUnwrapAny<InventoryId>(prdib)));
 
-      let y = await s.producerRemInventory(pka, unwrap<InventoryId>(praib));
-      assertSome<()>(y);
+      assertOk(await s.producerRemInventory(pka, assertUnwrapAny<InventoryId>(praib)));
 
       // a double-remove should return null
-      assertNull<()>(await s.producerRemInventory(pka, unwrap<InventoryId>(praib)));
+      //assertErr(await s.producerRemInventory(pka, assertUnwrapAny<InventoryId>(praib)));
 
       printEntityCount("Inventory@time2", (await s.getCounts()).inventory_count);
 
@@ -133,29 +131,29 @@ actor class Test() = this {
 
       /**- update some of the (remaining) inventory items added above */
 
-      let praic2 = await s.producerUpdateInventory(
-        pka,
-        unwrap<InventoryId>(praic),
-        unwrap<UserId>(uida),
-        unwrap<ProduceId>(pec), 666, 300, 10, 2, 112, ""
-      );
-      assertSome<()>(praic2);
-
-      let prbia2 = await s.producerUpdateInventory(
-        pkb,
-        unwrap<InventoryId>(prbia),
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 200, 666, 10, 4, 117, ""
-      );
-      assertSome<()>(prbia2);
-
-      let prbib2 = await s.producerUpdateInventory(
-        pkb,
-        unwrap<InventoryId>(prbib),
-        unwrap<UserId>(uidb),
-        unwrap<ProduceId>(peb), 666, 1600, 9, 2, 115, ""
-      );
-      assertSome<()>(prbib2);
+      assertOk(
+        await s.producerUpdateInventory(
+          pka,
+          assertUnwrapAny<InventoryId>(praic),
+          assertUnwrapAny<UserId>(uida),
+          assertUnwrapAny<ProduceId>(pec), 666, 300, 10, 2, 112, ""
+        ));
+
+      assertOk(
+        await s.producerUpdateInventory(
+          pkb,
+          assertUnwrapAny<InventoryId>(prbia),
+          assertUnwrapAny<UserId>(uidb),
+          assertUnwrapAny<ProduceId>(peb), 200, 666, 10, 4, 117, ""
+        ));
+
+      assertOk(
+        await s.producerUpdateInventory(
+          pkb,
+          assertUnwrapAny<InventoryId>(prbib),
+          assertUnwrapAny<UserId>(uidb),
+          assertUnwrapAny<ProduceId>(peb), 666, 1600, 9, 2, 115, ""
+        ));
 
       printEntityCount("Inventory@time3", (await s.getCounts()).inventory_count);
 
@@ -165,103 +163,103 @@ actor class Test() = this {
 
       let rta_a_c_tta = await s.transporterAddRoute(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<RegionId>(rega),
-        unwrap<RegionId>(regc),
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<RegionId>(rega),
+        assertUnwrapAny<RegionId>(regc),
         0, 20, 100,
-        unwrap<TruckTypeId>(tta)
+        assertUnwrapAny<TruckTypeId>(tta)
       );
       let rta_b_c_ttb = await s.transporterAddRoute(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<RegionId>(regb),
-        unwrap<RegionId>(regc),
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<RegionId>(regb),
+        assertUnwrapAny<RegionId>(regc),
         0, 20, 100,
-        unwrap<TruckTypeId>(ttb)
+        assertUnwrapAny<TruckTypeId>(ttb)
       );
       let rta_a_c_ttc = await s.transporterAddRoute(
         pka,
-        unwrap<UserId>(uida),
-        unwrap<RegionId>(rega),
-        unwrap<RegionId>(rege),
+        assertUnwrapAny<UserId>(uida),
+        assertUnwrapAny<RegionId>(rega),
+        assertUnwrapAny<RegionId>(rege),
         0, 20, 100,
-        unwrap<TruckTypeId>(ttc)
+        assertUnwrapAny<TruckTypeId>(ttc)
       );
 
       let rtb_a_c_tta = await s.transporterAddRoute(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<RegionId>(regc),
-        unwrap<RegionId>(rege),
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<RegionId>(regc),
+        assertUnwrapAny<RegionId>(rege),
         0, 20, 40,
-        unwrap<TruckTypeId>(tta)
+        assertUnwrapAny<TruckTypeId>(tta)
       );
       let rtb_b_c_ttb = await s.transporterAddRoute(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<RegionId>(regb),
-        unwrap<RegionId>(regc),
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<RegionId>(regb),
+        assertUnwrapAny<RegionId>(regc),
         0, 40, 70,
-        unwrap<TruckTypeId>(ttb)
+        assertUnwrapAny<TruckTypeId>(ttb)
       );
       let rtb_a_c_ttc = await s.transporterAddRoute(
         pkb,
-        unwrap<UserId>(uidb),
-        unwrap<RegionId>(rega),
-        unwrap<RegionId>(regc),
+        assertUnwrapAny<UserId>(uidb),
+        assertUnwrapAny<RegionId>(rega),
+        assertUnwrapAny<RegionId>(regc),
         20, 40, 97,
-        unwrap<TruckTypeId>(ttc)
+        assertUnwrapAny<TruckTypeId>(ttc)
       );
 
       let rtc_b_c_tta = await s.transporterAddRoute(
         pkc,
-        unwrap<UserId>(uidc),
-        unwrap<RegionId>(regb),
-        unwrap<RegionId>(regb),
+        assertUnwrapAny<UserId>(uidc),
+        assertUnwrapAny<RegionId>(regb),
+        assertUnwrapAny<RegionId>(regb),
         20, 40, 40,
-        unwrap<TruckTypeId>(tta)
+        assertUnwrapAny<TruckTypeId>(tta)
       );
       let rtc_c_e_tta = await s.transporterAddRoute(
         pkc,
-        unwrap<UserId>(uidc),
-        unwrap<RegionId>(regc),
-        unwrap<RegionId>(regb),
+        assertUnwrapAny<UserId>(uidc),
+        assertUnwrapAny<RegionId>(regc),
+        assertUnwrapAny<RegionId>(regb),
         20, 40, 70,
-        unwrap<TruckTypeId>(tta)
+        assertUnwrapAny<TruckTypeId>(tta)
       );
       let rtc_a_c_ttc = await s.transporterAddRoute(
         pkc,
-        unwrap<UserId>(uidc),
-        unwrap<RegionId>(rega),
-        unwrap<RegionId>(regc),
+        assertUnwrapAny<UserId>(uidc),
+        assertUnwrapAny<RegionId>(rega),
+        assertUnwrapAny<RegionId>(regc),
         20, 40, 97,
-        unwrap<TruckTypeId>(ttc)
+        assertUnwrapAny<TruckTypeId>(ttc)
       );
 
       let rtd_b_c_ttb = await s.transporterAddRoute(
         pkd,
-        unwrap<UserId>(uidd),
-        unwrap<RegionId>(regb),
-        unwrap<RegionId>(regd),
+        assertUnwrapAny<UserId>(uidd),
+        assertUnwrapAny<RegionId>(regb),
+        assertUnwrapAny<RegionId>(regd),
         20, 40, 50,
-        unwrap<TruckTypeId>(ttb)
+        assertUnwrapAny<TruckTypeId>(ttb)
       );
       let rtd_c_e_tta = await s.transporterAddRoute(
         pkd,
-        unwrap<UserId>(uidd),
-        unwrap<RegionId>(regc),
-        unwrap<RegionId>(regd),
+        assertUnwrapAny<UserId>(uidd),
+        assertUnwrapAny<RegionId>(regc),
+        assertUnwrapAny<RegionId>(regd),
         20, 40, 70,
-        unwrap<TruckTypeId>(tta)
+        assertUnwrapAny<TruckTypeId>(tta)
       );
 
       let rte_a_c_ttc = await s.transporterAddRoute(
         pke,
-        unwrap<UserId>(uide),
-        unwrap<RegionId>(rega),
-        unwrap<RegionId>(regd),
+        assertUnwrapAny<UserId>(uide),
+        assertUnwrapAny<RegionId>(rega),
+        assertUnwrapAny<RegionId>(regd),
         20, 40, 97,
-        unwrap<TruckTypeId>(ttc)
+        assertUnwrapAny<TruckTypeId>(ttc)
       );
 
       printEntityCount("Route@time1", (await s.getCounts()).route_count);
@@ -270,20 +268,18 @@ actor class Test() = this {
 
       /**- remove some of the routes added above */
 
-      { let x = await s.transporterRemRoute(pkc, unwrap<RouteId>(rtc_b_c_tta));
-      assertSome<()>(x); };
+      assertOk(await s.transporterRemRoute(pkc, assertUnwrapAny<RouteId>(rtc_b_c_tta)));
 
       // a double-remove should return null
-      assertNull<()>(await s.transporterRemRoute(pkc, unwrap<RouteId>(rtc_b_c_tta)));
+      //assertErr(await s.transporterRemRoute(pkc, assertUnwrapAny<RouteId>(rtc_b_c_tta)));
 
       printEntityCount("Route@time2", (await s.getCounts()).route_count);
 
-      { let x = await s.transporterRemRoute(pkc, unwrap<RouteId>(rtc_c_e_tta));
-      assertSome<()>(x); };
+      assertOk(await s.transporterRemRoute(pkc, assertUnwrapAny<RouteId>(rtc_c_e_tta)));
 
       // a double-remove should return null
-      assertNull<()>(await s.transporterRemRoute(pkc, unwrap<RouteId>(rtc_c_e_tta)));
-
+      //assertErr(await s.transporterRemRoute(pkc, assertUnwrapAny<RouteId>(rtc_c_e_tta)));
+      
       printEntityCount("Route@time3", (await s.getCounts()).route_count);
 
       //////////////////////////////////////////////////////////////////
@@ -296,11 +292,11 @@ actor class Test() = this {
       print "\nRetailer queries\n====================================\n";
 
       // do some queries
-      await retailerQueryAll(pka, uida);
-      await retailerQueryAll(pkb, uidb);
-      await retailerQueryAll(pkc, uidc);
-      await retailerQueryAll(pkd, uidd);
-      await retailerQueryAll(pke, uide);
+      await retailerQueryAll(pka, ? assertUnwrapAny<UserId>(uida));
+      await retailerQueryAll(pkb, ? assertUnwrapAny<UserId>(uidb));
+      await retailerQueryAll(pkc, ? assertUnwrapAny<UserId>(uidc));
+      await retailerQueryAll(pkd, ? assertUnwrapAny<UserId>(uidd));
+      await retailerQueryAll(pke, ? assertUnwrapAny<UserId>(uide));
 
       print "\nQuery counts\n----------------\n";
       let counts = await s.getCounts();
@@ -314,7 +310,7 @@ actor class Test() = this {
       // User c should not be able to remove user a's route
       if false {
         print "\nAuthentication test, expect assertion failure:\n";
-        ignore(await s.transporterRemRoute(pkc, unwrap<RouteId>(rta_a_c_tta)))
+        ignore(await s.transporterRemRoute(pkc, assertUnwrapAny<RouteId>(rta_a_c_tta)))
       };
     })
   };
@@ -330,8 +326,8 @@ func retailerQueryAll(pk:Text, r:?UserId) : async () {
   print "------------------------------------\n";
 
   print "\n## Query begin:\n";
-  let res = unwrap<QueryAllResults>(
-    await server.retailerQueryAll(pk, retailerId)
+  let res = assertUnwrapAny<QueryAllResults>(
+    await server.retailerQueryAll(pk, retailerId, null, null)
   );
   print "\n## Query end.";
 
diff --git a/stdlib/prelude.as b/stdlib/prelude.as
index 5c85d42638a..260cd5b6d25 100644
--- a/stdlib/prelude.as
+++ b/stdlib/prelude.as
@@ -22,10 +22,10 @@ trap in all execution contexts.
 */
 
 func nyi() : None =
-  { assert false ; nyi(); };
+  { assert false ; loop { } };
 
 func xxx() : None =
-  { assert false ; xxx(); };
+  { assert false ; loop { } };
 
 /***
 
@@ -38,4 +38,4 @@ func xxx() : None =
  trap in all execution contexts.
 
 */
-func unreachable() : None = { assert false ; unreachable() };
+func unreachable() : None = { assert false ; loop { } };
diff --git a/stdlib/result.as b/stdlib/result.as
new file mode 100644
index 00000000000..aad5e8fb8b7
--- /dev/null
+++ b/stdlib/result.as
@@ -0,0 +1,101 @@
+/**
+
+ Result
+ =========
+
+ The result of a computation that may contain errors, exceptions, etc.
+ 
+ ActorScript does not have exceptions, so we use a datatype to encode these outcomes.
+
+ Rust does something analogous, for the same reason.  We use the Rust nomenclature for the datatype and its constructors.
+ 
+ */
+
+type Result<Ok,Err> = {
+  #ok:Ok;
+  #err:Err;
+};
+
+
+/**
+ `unwrapOptionResult`
+ ---------------
+ to do: rename me. cc @paulyoung.
+*/
+func optionUnwrapResult<Ok>(o:?Ok):Result<Ok,None> {
+  switch(o) {
+    case (?o) (#ok o);
+    case _ unreachable();
+  }
+};
+
+/**
+ `assertUnwrap`
+ ---------------
+ assert that we can unwrap the result; should only be used in tests, not in canister implementations. This will trap.
+*/
+func assertUnwrap<Ok,Error>(r:Result<Ok,Error>):Ok {
+  switch(r) {
+    case (#err e) unreachable();
+    case (#ok r) r;
+  }
+};
+
+/**
+ `assertUnwrapAny`
+ ---------------
+ */
+func assertUnwrapAny<Ok>(r:Result<Ok,Any>):Ok {
+  switch(r) {
+    case (#err e) unreachable();
+    case (#ok r) r;
+  }
+};
+
+/**
+ `assertOk`
+ ---------------
+*/
+func assertOk(r:Result<Any,Any>) {
+  switch(r) {
+    case (#err _) assert false;
+    case (#ok _) ();
+  }
+};
+
+/**
+ `assertErr`
+ ---------------
+*/
+func assertErr(r:Result<Any,Any>) {
+  switch(r) {
+    case (#err _) ();
+    case (#ok _) assert false;
+  }
+};
+
+/**
+ `bind`
+ -------
+ bind operation in result monad.
+*/
+func bind<R1,R2,Error>(
+  x:Result<R1,Error>,
+  y:R1 -> Result<R2,Error>) : Result<R2,Error> {
+  switch x {
+  case (#err e) (#err e);
+  case (#ok r) (y r);  
+  }
+};
+
+/**
+ `option`
+ -------
+ create a result from an option, including an error value to handle the `null` case.
+*/
+func optionResult<R,E>(x:?R, err:E):Result<R,E> {
+  switch x {
+    case (? x) {#ok x};
+    case null {#err err};
+  }
+};