diff --git a/samples/hotelManagement/.vscode/settings.json b/samples/hotelManagement/.vscode/settings.json
index 8f94129f..2d91860e 100644
--- a/samples/hotelManagement/.vscode/settings.json
+++ b/samples/hotelManagement/.vscode/settings.json
@@ -4,7 +4,9 @@
   "editor.formatOnSave": true,
 
   "editor.codeActionsOnSave": {
-    "source.fixAll.eslint": "explicit"
+    "source.organizeImports": "explicit",
+    "source.fixAll.eslint": "explicit",
+    "source.addMissingImports": "always"
   },
 
   "editor.tabSize": 2,
@@ -13,5 +15,7 @@
     "node_modules/": true,
     "dist/": true
   },
-  "files.eol": "\n"
+  "files.eol": "\n",
+
+  "typescript.preferences.importModuleSpecifier": "relative"
 }
diff --git a/samples/hotelManagement/package-lock.json b/samples/hotelManagement/package-lock.json
index acc7ff2f..526f9a43 100644
--- a/samples/hotelManagement/package-lock.json
+++ b/samples/hotelManagement/package-lock.json
@@ -16,7 +16,8 @@
         "dotenv-cli": "7.3.0",
         "express": "4.18.2",
         "immutable": "5.0.0-beta.4",
-        "mongodb": "6.3.0"
+        "mongodb": "6.3.0",
+        "ts-essentials": "9.4.1"
       },
       "devDependencies": {
         "@types/convict": "6.1.6",
@@ -8661,6 +8662,19 @@
         "typescript": ">=4.2.0"
       }
     },
+    "node_modules/ts-essentials": {
+      "version": "9.4.1",
+      "resolved": "https://registry.npmjs.org/ts-essentials/-/ts-essentials-9.4.1.tgz",
+      "integrity": "sha512-oke0rI2EN9pzHsesdmrOrnqv1eQODmJpd/noJjwj2ZPC3Z4N2wbjrOEqnsEgmvlO2+4fBb0a794DCna2elEVIQ==",
+      "peerDependencies": {
+        "typescript": ">=4.1.0"
+      },
+      "peerDependenciesMeta": {
+        "typescript": {
+          "optional": true
+        }
+      }
+    },
     "node_modules/ts-jest": {
       "version": "29.1.1",
       "resolved": "https://registry.npmjs.org/ts-jest/-/ts-jest-29.1.1.tgz",
@@ -8831,7 +8845,7 @@
       "version": "5.3.3",
       "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.3.3.tgz",
       "integrity": "sha512-pXWcraxM0uxAS+tN0AG/BF2TyqmHO014Z070UsJ+pFvYuRSq8KH8DmWpnbXe0pEPDHXZV3FcAbJkijJ5oNEnWw==",
-      "dev": true,
+      "devOptional": true,
       "bin": {
         "tsc": "bin/tsc",
         "tsserver": "bin/tsserver"
@@ -15880,6 +15894,12 @@
       "dev": true,
       "requires": {}
     },
+    "ts-essentials": {
+      "version": "9.4.1",
+      "resolved": "https://registry.npmjs.org/ts-essentials/-/ts-essentials-9.4.1.tgz",
+      "integrity": "sha512-oke0rI2EN9pzHsesdmrOrnqv1eQODmJpd/noJjwj2ZPC3Z4N2wbjrOEqnsEgmvlO2+4fBb0a794DCna2elEVIQ==",
+      "requires": {}
+    },
     "ts-jest": {
       "version": "29.1.1",
       "resolved": "https://registry.npmjs.org/ts-jest/-/ts-jest-29.1.1.tgz",
@@ -15982,7 +16002,7 @@
       "version": "5.3.3",
       "resolved": "https://registry.npmjs.org/typescript/-/typescript-5.3.3.tgz",
       "integrity": "sha512-pXWcraxM0uxAS+tN0AG/BF2TyqmHO014Z070UsJ+pFvYuRSq8KH8DmWpnbXe0pEPDHXZV3FcAbJkijJ5oNEnWw==",
-      "dev": true
+      "devOptional": true
     },
     "unbox-primitive": {
       "version": "1.0.1",
diff --git a/samples/hotelManagement/package.json b/samples/hotelManagement/package.json
index 409827b0..c19d1dfe 100644
--- a/samples/hotelManagement/package.json
+++ b/samples/hotelManagement/package.json
@@ -41,7 +41,8 @@
     "dotenv-cli": "7.3.0",
     "express": "4.18.2",
     "immutable": "5.0.0-beta.4",
-    "mongodb": "6.3.0"
+    "mongodb": "6.3.0",
+    "ts-essentials": "9.4.1"
   },
   "devDependencies": {
     "@types/convict": "6.1.6",
diff --git a/samples/hotelManagement/src/core/command.ts b/samples/hotelManagement/src/core/command.ts
index 9225c029..f598ed62 100644
--- a/samples/hotelManagement/src/core/command.ts
+++ b/samples/hotelManagement/src/core/command.ts
@@ -1,7 +1,12 @@
+import { Flavour } from './typing';
+
 export type Command<
   CommandType extends string = string,
   CommandData extends Record<string, unknown> = Record<string, unknown>,
-> = Readonly<{
-  type: Readonly<CommandType>;
-  data: Readonly<CommandData>;
-}>;
+> = Flavour<
+  Readonly<{
+    type: Readonly<CommandType>;
+    data: Readonly<CommandData>;
+  }>,
+  'Command'
+>;
diff --git a/samples/hotelManagement/src/core/event.ts b/samples/hotelManagement/src/core/event.ts
index 343d37e6..8c2d6662 100644
--- a/samples/hotelManagement/src/core/event.ts
+++ b/samples/hotelManagement/src/core/event.ts
@@ -1,7 +1,12 @@
+import { Flavour } from './typing';
+
 export type Event<
   EventType extends string = string,
   EventData extends Record<string, unknown> = Record<string, unknown>,
-> = Readonly<{
-  type: Readonly<EventType>;
-  data: Readonly<EventData>;
-}>;
+> = Flavour<
+  Readonly<{
+    type: Readonly<EventType>;
+    data: Readonly<EventData>;
+  }>,
+  'Event'
+>;
diff --git a/samples/hotelManagement/src/core/processManager.ts b/samples/hotelManagement/src/core/processManager.ts
deleted file mode 100644
index 0dd33842..00000000
--- a/samples/hotelManagement/src/core/processManager.ts
+++ /dev/null
@@ -1,29 +0,0 @@
-import { Event } from './event';
-import { Command } from './command';
-
-export type EnqueuedEvent<EventType extends Event> = Readonly<{
-  type: 'Event';
-  data: EventType;
-}>;
-
-export type ScheduledCommand<CommandType extends Command> = Readonly<{
-  type: 'Command';
-  data: CommandType;
-}>;
-
-export type ProcesssingResult<
-  CommandType extends Command,
-  EventType extends Event,
-> = ScheduledCommand<CommandType> | EnqueuedEvent<EventType>;
-
-export const enqueue = <EventType extends Event>(
-  event: EventType,
-): EnqueuedEvent<EventType> => {
-  return { type: 'Event', data: event };
-};
-
-export const schedule = <CommandType extends Command>(
-  command: CommandType,
-): ScheduledCommand<CommandType> => {
-  return { type: 'Command', data: command };
-};
diff --git a/samples/hotelManagement/src/core/typing.ts b/samples/hotelManagement/src/core/typing.ts
new file mode 100644
index 00000000..0b5cb6fb
--- /dev/null
+++ b/samples/hotelManagement/src/core/typing.ts
@@ -0,0 +1,2 @@
+export type Brand<K, T> = K & { readonly __brand: T };
+export type Flavour<K, T> = K & { readonly __brand?: T };
diff --git a/samples/hotelManagement/src/core/workflow.ts b/samples/hotelManagement/src/core/workflow.ts
new file mode 100644
index 00000000..96747378
--- /dev/null
+++ b/samples/hotelManagement/src/core/workflow.ts
@@ -0,0 +1,19 @@
+import { Command } from './command';
+import { Event } from './event';
+
+/// Inspired by https://blog.bittacklr.be/the-workflow-pattern.html
+
+export type WorkflowEvent<Output extends Command | Event> = Extract<
+  Output,
+  { __brand?: 'Event' }
+>;
+
+export type Workflow<
+  Input extends Event | Command,
+  State,
+  Output extends Event | Command,
+> = {
+  decide: (command: Input, state: State) => Output[];
+  evolve: (currentState: State, event: WorkflowEvent<Output>) => State;
+  getInitialState: () => State;
+};
diff --git a/samples/hotelManagement/src/processManagers/groupCheckouts/groupCheckoutProcessManager.ts b/samples/hotelManagement/src/processManagers/groupCheckouts/groupCheckoutProcessManager.ts
index 4d7ecda0..5c511bb7 100644
--- a/samples/hotelManagement/src/processManagers/groupCheckouts/groupCheckoutProcessManager.ts
+++ b/samples/hotelManagement/src/processManagers/groupCheckouts/groupCheckoutProcessManager.ts
@@ -1,6 +1,5 @@
-import { Map } from 'immutable';
 import { Command } from '#core/command';
-import { enqueue, ProcesssingResult, schedule } from '#core/processManager';
+import { Map } from 'immutable';
 import {
   CheckOut,
   GuestCheckedOut,
@@ -19,10 +18,7 @@ export type GroupCheckoutProcessManagerEvent =
   | GuestCheckedOut
   | GuestCheckoutFailed;
 
-export type GroupCheckoutProcessingResult = ProcesssingResult<
-  CheckOut,
-  GroupCheckoutEvent
->;
+export type GroupCheckoutProcessingResult = CheckOut | GroupCheckoutEvent;
 
 export type InitiateGroupCheckout = Command<
   'InitiateGroupCheckout',
@@ -68,27 +64,29 @@ export const GroupCheckoutProcessManager = (
 
       if (state.status === 'Finished') return [];
 
-      const checkoutGuestStays = event.guestStayAccountIds.map((id) => {
-        return schedule<CheckOut>({
-          type: 'CheckOut',
-          data: {
-            guestStayAccountId: id,
-            now: event.initiatedAt,
-            groupCheckoutId: event.groupCheckoutId,
-          },
-        });
-      });
+      const checkoutGuestStays: CheckOut[] = event.guestStayAccountIds.map(
+        (id) => {
+          return {
+            type: 'CheckOut',
+            data: {
+              guestStayAccountId: id,
+              now: event.initiatedAt,
+              groupCheckoutId: event.groupCheckoutId,
+            },
+          };
+        },
+      );
 
       return [
         ...checkoutGuestStays,
-        enqueue({
+        {
           type: 'GuestCheckoutsInitiated',
           data: {
             groupCheckoutId: event.groupCheckoutId,
             initiatedGuestStayIds: event.guestStayAccountIds,
             initiatedAt: event.initiatedAt,
           },
-        }),
+        },
       ];
     }
 
@@ -137,11 +135,8 @@ export const GroupCheckoutProcessManager = (
             };
 
       return areAnyOngoingCheckouts(guestStayAccountIds)
-        ? enqueue(finished)
-        : [
-            enqueue(finished),
-            enqueue(finish(groupCheckoutId, state.guestStayAccountIds, now)),
-          ];
+        ? finished
+        : [finished, finish(groupCheckoutId, state.guestStayAccountIds, now)];
     }
   }
 };
diff --git a/samples/hotelManagement/src/workflows/groupCheckouts/groupCheckoutWorflow.ts b/samples/hotelManagement/src/workflows/groupCheckouts/groupCheckoutWorflow.ts
new file mode 100644
index 00000000..99743d1a
--- /dev/null
+++ b/samples/hotelManagement/src/workflows/groupCheckouts/groupCheckoutWorflow.ts
@@ -0,0 +1,386 @@
+import { Command } from '#core/command';
+import { Event } from '#core/event';
+import { Workflow, WorkflowEvent } from '#core/workflow';
+import { Map } from 'immutable';
+import {
+  CheckOut,
+  GuestCheckedOut,
+  GuestCheckoutFailed,
+} from '../guestStayAccounts/guestStayAccount';
+
+/// Inspired by https://blog.bittacklr.be/the-workflow-pattern.html
+
+////////////////////////////////////////////
+////////// Commands
+///////////////////////////////////////////
+
+export type InitiateGroupCheckout = Command<
+  'InitiateGroupCheckout',
+  {
+    groupCheckoutId: string;
+    clerkId: string;
+    guestStayAccountIds: string[];
+    now: Date;
+  }
+>;
+
+////////////////////////////////////////////
+////////// EVENTS
+///////////////////////////////////////////
+
+export type GroupCheckoutInitiated = Event<
+  'GroupCheckoutInitiated',
+  {
+    groupCheckoutId: string;
+    clerkId: string;
+    guestStayAccountIds: string[];
+    initiatedAt: Date;
+  }
+>;
+
+export type GuestCheckoutsInitiated = Event<
+  'GuestCheckoutsInitiated',
+  {
+    groupCheckoutId: string;
+    initiatedGuestStayIds: string[];
+    initiatedAt: Date;
+  }
+>;
+
+export type GuestCheckoutCompletionRecorded = Event<
+  'GuestCheckoutCompletionRecorded',
+  {
+    groupCheckoutId: string;
+    guestStayAccountId: string;
+    completedAt: Date;
+  }
+>;
+
+export type GuestCheckoutFailureRecorded = Event<
+  'GuestCheckoutFailureRecorded',
+  {
+    groupCheckoutId: string;
+    guestStayAccountId: string;
+    failedAt: Date;
+  }
+>;
+
+export type GroupCheckoutCompleted = Event<
+  'GroupCheckoutCompleted',
+  {
+    groupCheckoutId: string;
+    completedCheckouts: string[];
+    completedAt: Date;
+  }
+>;
+
+export type GroupCheckoutFailed = Event<
+  'GroupCheckoutFailed',
+  {
+    groupCheckoutId: string;
+    completedCheckouts: string[];
+    failedCheckouts: string[];
+    failedAt: Date;
+  }
+>;
+
+export type GroupCheckoutEvent =
+  | GroupCheckoutInitiated
+  | GuestCheckoutsInitiated
+  | GuestCheckoutCompletionRecorded
+  | GuestCheckoutFailureRecorded
+  | GroupCheckoutCompleted
+  | GroupCheckoutFailed;
+
+////////////////////////////////////////////
+////////// Entity
+///////////////////////////////////////////
+
+export type GroupCheckout =
+  | { status: 'NotExisting' }
+  | {
+      status: 'Pending';
+      guestStayAccountIds: Map<string, GuestStayStatus>;
+    }
+  | { status: 'Finished' };
+
+export const getInitialState = (): GroupCheckout => {
+  return {
+    status: 'NotExisting',
+  };
+};
+
+export enum GuestStayStatus {
+  Pending = 'Pending',
+  Initiated = 'Initiated',
+  Completed = 'Completed',
+  Failed = 'Failed',
+}
+
+////////////////////////////////////////////
+////////// Workflow Definition
+///////////////////////////////////////////
+
+export type GroupCheckoutInput =
+  | InitiateGroupCheckout
+  | GuestCheckedOut
+  | GuestCheckoutFailed;
+
+export type GroupCheckoutOutput =
+  | GroupCheckoutInitiated
+  | CheckOut
+  | GuestCheckoutCompletionRecorded
+  | GuestCheckoutFailureRecorded
+  | GuestCheckoutsInitiated
+  | GroupCheckoutCompleted
+  | GroupCheckoutFailed
+  | Ignored
+  | UnexpectedErrorOcurred;
+export type Ignored = {
+  type: 'Ignored';
+  data: {
+    reason: IgnoredReason;
+  };
+};
+
+export type UnexpectedErrorOcurred = {
+  type: 'ErrorOcurred';
+  data: {
+    reason: ErrorReason;
+  };
+};
+
+export type IgnoredReason =
+  | 'GroupCheckoutAlreadyInitiated'
+  | 'GuestCheckoutsInitiationAlreadyRecorded'
+  | 'GuestCheckoutAlreadyFinished'
+  | 'GroupCheckoutAlreadyFinished'
+  | 'GroupCheckoutDoesNotExist';
+
+export type ErrorReason = 'UnknownInputType';
+
+const ignore = (reason: IgnoredReason): Ignored => {
+  return {
+    type: 'Ignored',
+    data: {
+      reason,
+    },
+  };
+};
+
+const error = (reason: ErrorReason): UnexpectedErrorOcurred => {
+  return {
+    type: 'ErrorOcurred',
+    data: {
+      reason,
+    },
+  };
+};
+
+////////////////////////////////////////////
+////////// Evolve
+///////////////////////////////////////////
+
+export const decide = (
+  input: GroupCheckoutInput,
+  state: GroupCheckout,
+): GroupCheckoutOutput[] => {
+  const { type, data } = input;
+
+  switch (type) {
+    case 'InitiateGroupCheckout': {
+      if (state.status !== 'NotExisting')
+        return [ignore('GroupCheckoutAlreadyInitiated')];
+
+      const checkoutGuestStays = data.guestStayAccountIds.map<CheckOut>(
+        (id) => {
+          return {
+            type: 'CheckOut',
+            data: {
+              guestStayAccountId: id,
+              now: data.now,
+              groupCheckoutId: data.groupCheckoutId,
+            },
+          };
+        },
+      );
+
+      return [
+        {
+          type: 'GuestCheckoutsInitiated',
+          data: {
+            groupCheckoutId: data.groupCheckoutId,
+            initiatedGuestStayIds: data.guestStayAccountIds,
+            initiatedAt: data.now,
+          },
+        },
+        ...checkoutGuestStays,
+      ];
+    }
+    case 'GuestCheckedOut':
+    case 'GuestCheckoutFailed': {
+      if (!data.groupCheckoutId) return [];
+
+      if (state.status === 'NotExisting') return [];
+
+      if (state.status === 'Finished') return [];
+
+      const { guestStayAccountId, groupCheckoutId } = data;
+
+      const guestCheckoutStatus =
+        state.guestStayAccountIds.get(guestStayAccountId);
+
+      if (isAlreadyClosed(guestCheckoutStatus)) return [];
+
+      const guestStayAccountIds = state.guestStayAccountIds.set(
+        guestStayAccountId,
+        type === 'GuestCheckedOut'
+          ? GuestStayStatus.Completed
+          : GuestStayStatus.Failed,
+      );
+
+      const now =
+        type === 'GuestCheckedOut' ? data.checkedOutAt : data.failedAt;
+
+      const finished: GroupCheckoutEvent =
+        type === 'GuestCheckedOut'
+          ? {
+              type: 'GuestCheckoutCompletionRecorded',
+              data: {
+                groupCheckoutId,
+                guestStayAccountId,
+                completedAt: now,
+              },
+            }
+          : {
+              type: 'GuestCheckoutFailureRecorded',
+              data: {
+                groupCheckoutId,
+                guestStayAccountId,
+                failedAt: now,
+              },
+            };
+
+      return areAnyOngoingCheckouts(guestStayAccountIds)
+        ? [finished]
+        : [finished, finish(groupCheckoutId, state.guestStayAccountIds, now)];
+    }
+    default: {
+      const _notExistingEventType: never = type;
+      return [error('UnknownInputType')];
+    }
+  }
+};
+
+export const evolve = (
+  state: GroupCheckout,
+  { type, data: event }: WorkflowEvent<GroupCheckoutOutput>,
+): GroupCheckout => {
+  switch (type) {
+    case 'GroupCheckoutInitiated': {
+      if (state.status !== 'NotExisting') return state;
+
+      return {
+        status: 'Pending',
+        guestStayAccountIds: event.guestStayAccountIds.reduce(
+          (map, id) => map.set(id, GuestStayStatus.Pending),
+          Map<string, GuestStayStatus>(),
+        ),
+      };
+    }
+    case 'GuestCheckoutsInitiated': {
+      if (state.status !== 'Pending') return state;
+
+      return {
+        status: 'Pending',
+        guestStayAccountIds: event.initiatedGuestStayIds.reduce(
+          (map, id) => map.set(id, GuestStayStatus.Initiated),
+          state.guestStayAccountIds,
+        ),
+      };
+    }
+    case 'GuestCheckoutCompletionRecorded':
+    case 'GuestCheckoutFailureRecorded': {
+      if (state.status !== 'Pending') return state;
+
+      return {
+        ...state,
+        guestStayAccountIds: state.guestStayAccountIds.set(
+          event.guestStayAccountId,
+          type === 'GuestCheckoutCompletionRecorded'
+            ? GuestStayStatus.Completed
+            : GuestStayStatus.Failed,
+        ),
+      };
+    }
+    case 'GroupCheckoutCompleted':
+    case 'GroupCheckoutFailed': {
+      if (state.status !== 'Pending') return state;
+
+      return {
+        status: 'Finished',
+      };
+    }
+    default: {
+      const _notExistingEventType: never = type;
+      return state;
+    }
+  }
+};
+
+export const GroupCheckoutWorkflow: Workflow<
+  GroupCheckoutInput,
+  GroupCheckout,
+  GroupCheckoutOutput
+> = {
+  decide,
+  evolve,
+  getInitialState,
+};
+
+export const isAlreadyClosed = (status: GuestStayStatus | undefined) =>
+  status === GuestStayStatus.Completed || status === GuestStayStatus.Failed;
+
+const areAnyOngoingCheckouts = (
+  guestStayAccounts: Map<string, GuestStayStatus>,
+) => guestStayAccounts.some((status) => !isAlreadyClosed(status));
+
+const areAllCompleted = (guestStayAccounts: Map<string, GuestStayStatus>) =>
+  guestStayAccounts.some((status) => status === GuestStayStatus.Completed);
+
+const checkoutsWith = (
+  guestStayAccounts: Map<string, GuestStayStatus>,
+  status: GuestStayStatus,
+): string[] =>
+  Array.from(guestStayAccounts.filter((s) => s === status).values());
+
+const finish = (
+  groupCheckoutId: string,
+  guestStayAccounts: Map<string, GuestStayStatus>,
+  now: Date,
+): GroupCheckoutEvent => {
+  return areAllCompleted(guestStayAccounts)
+    ? {
+        type: 'GroupCheckoutCompleted',
+        data: {
+          groupCheckoutId,
+          completedCheckouts: Array.from(guestStayAccounts.values()),
+          completedAt: now,
+        },
+      }
+    : {
+        type: 'GroupCheckoutFailed',
+        data: {
+          groupCheckoutId,
+          completedCheckouts: checkoutsWith(
+            guestStayAccounts,
+            GuestStayStatus.Completed,
+          ),
+          failedCheckouts: checkoutsWith(
+            guestStayAccounts,
+            GuestStayStatus.Failed,
+          ),
+          failedAt: now,
+        },
+      };
+};
diff --git a/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccount.ts b/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccount.ts
new file mode 100644
index 00000000..6f323aad
--- /dev/null
+++ b/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccount.ts
@@ -0,0 +1,245 @@
+import { Command } from '#core/command';
+import { Event } from '#core/event';
+
+////////////////////////////////////////////
+////////// EVENTS
+///////////////////////////////////////////
+
+export type GuestCheckedIn = Event<
+  'GuestCheckedIn',
+  {
+    guestStayAccountId: string;
+    checkedInAt: Date;
+  }
+>;
+
+export type ChargeRecorded = Event<
+  'ChargeRecorded',
+  {
+    guestStayAccountId: string;
+    amount: number;
+    recordedAt: Date;
+  }
+>;
+
+export type PaymentRecorded = Event<
+  'PaymentRecorded',
+  {
+    guestStayAccountId: string;
+    amount: number;
+    recordedAt: Date;
+  }
+>;
+export type GuestCheckedOut = Event<
+  'GuestCheckedOut',
+  {
+    guestStayAccountId: string;
+    checkedOutAt: Date;
+    groupCheckoutId?: string;
+  }
+>;
+
+export type GuestCheckoutFailed = Event<
+  'GuestCheckoutFailed',
+  {
+    guestStayAccountId: string;
+    reason: 'NotOpened' | 'BalanceNotSettled';
+    failedAt: Date;
+    groupCheckoutId?: string;
+  }
+>;
+
+export type GuestStayAccountEvent =
+  | GuestCheckedIn
+  | ChargeRecorded
+  | PaymentRecorded
+  | GuestCheckedOut
+  | GuestCheckoutFailed;
+
+////////////////////////////////////////////
+////////// Entity
+///////////////////////////////////////////
+
+export type GuestStayAccount =
+  | { status: 'NotExisting' }
+  | {
+      status: 'Opened';
+      balance: number;
+    }
+  | { status: 'CheckedOut' };
+
+////////////////////////////////////////////
+////////// Evolve
+///////////////////////////////////////////
+
+export const evolve = (
+  state: GuestStayAccount,
+  { type, data: event }: GuestStayAccountEvent,
+): GuestStayAccount => {
+  switch (type) {
+    case 'GuestCheckedIn': {
+      if (state.status !== 'NotExisting') return state;
+
+      return { status: 'Opened', balance: 0 };
+    }
+    case 'ChargeRecorded': {
+      if (state.status !== 'Opened') return state;
+
+      return {
+        ...state,
+        balance: state.balance - event.amount,
+      };
+    }
+    case 'PaymentRecorded': {
+      if (state.status !== 'Opened') return state;
+
+      return {
+        ...state,
+        balance: state.balance + event.amount,
+      };
+    }
+    case 'GuestCheckedOut': {
+      if (state.status !== 'Opened') return state;
+
+      return {
+        status: 'CheckedOut',
+      };
+    }
+    case 'GuestCheckoutFailed': {
+      return state;
+    }
+    default: {
+      const _notExistingEventType: never = type;
+      return state;
+    }
+  }
+};
+
+////////////////////////////////////////////
+////////// Commands
+///////////////////////////////////////////
+
+export type CheckIn = Command<
+  'CheckIn',
+  {
+    guestStayAccountId: string;
+    now: Date;
+  }
+>;
+export type RecordCharge = Command<
+  'RecordCharge',
+  {
+    guestStayAccountId: string;
+    amount: number;
+    now: Date;
+  }
+>;
+export type RecordPayment = Command<
+  'RecordPayment',
+  {
+    guestStayAccountId: string;
+    amount: number;
+    now: Date;
+  }
+>;
+export type CheckOut = Command<
+  'CheckOut',
+  {
+    guestStayAccountId: string;
+    now: Date;
+    groupCheckoutId?: string;
+  }
+>;
+
+export type GuestStayCommand =
+  | CheckIn
+  | RecordCharge
+  | RecordPayment
+  | CheckOut;
+
+export const decide = (
+  { type, data: command }: GuestStayCommand,
+  state: GuestStayAccount,
+): GuestStayAccountEvent => {
+  const { guestStayAccountId, now } = command;
+
+  switch (type) {
+    case 'CheckIn': {
+      if (state.status !== 'NotExisting')
+        throw Error('Guest is already checked-in!');
+
+      return {
+        type: 'GuestCheckedIn',
+        data: {
+          guestStayAccountId,
+          checkedInAt: now,
+        },
+      };
+    }
+    case 'RecordCharge': {
+      if (state.status !== 'Opened')
+        throw Error('Guest account is already checked out!');
+
+      return {
+        type: 'ChargeRecorded',
+        data: {
+          guestStayAccountId,
+          amount: command.amount,
+          recordedAt: now,
+        },
+      };
+    }
+    case 'RecordPayment': {
+      if (state.status !== 'Opened')
+        throw Error('Guest account is already checked out!');
+
+      return {
+        type: 'PaymentRecorded',
+        data: {
+          guestStayAccountId,
+          amount: command.amount,
+          recordedAt: now,
+        },
+      };
+    }
+    case 'CheckOut': {
+      if (state.status !== 'Opened')
+        return {
+          type: 'GuestCheckoutFailed',
+          data: {
+            guestStayAccountId,
+            groupCheckoutId: command.groupCheckoutId,
+            reason: 'NotOpened',
+            failedAt: now,
+          },
+        };
+
+      const isSettled = state.balance === 0;
+
+      if (!isSettled)
+        return {
+          type: 'GuestCheckoutFailed',
+          data: {
+            guestStayAccountId,
+            groupCheckoutId: command.groupCheckoutId,
+            reason: 'BalanceNotSettled',
+            failedAt: now,
+          },
+        };
+
+      return {
+        type: 'GuestCheckedOut',
+        data: {
+          guestStayAccountId,
+          groupCheckoutId: command.groupCheckoutId,
+          checkedOutAt: now,
+        },
+      };
+    }
+
+    default: {
+      const _notExistingCommandType: never = type;
+      throw new Error(`Unknown command type`);
+    }
+  }
+};
diff --git a/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccountDomainService.ts b/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccountDomainService.ts
new file mode 100644
index 00000000..1abc9fd5
--- /dev/null
+++ b/samples/hotelManagement/src/workflows/guestStayAccounts/guestStayAccountDomainService.ts
@@ -0,0 +1 @@
+export const nothing = {};
diff --git a/workshops/introduction_to_event_sourcing/.vscode/settings.json b/workshops/introduction_to_event_sourcing/.vscode/settings.json
index 8c5e9a4f..2d91860e 100644
--- a/workshops/introduction_to_event_sourcing/.vscode/settings.json
+++ b/workshops/introduction_to_event_sourcing/.vscode/settings.json
@@ -4,7 +4,7 @@
   "editor.formatOnSave": true,
 
   "editor.codeActionsOnSave": {
-    "source.organizeImports": true,
+    "source.organizeImports": "explicit",
     "source.fixAll.eslint": "explicit",
     "source.addMissingImports": "always"
   },