better example

README.md

@@ -10,8 +10,14 @@ gleam add eventsourcing
 import eventsourcing
 import eventsourcing/memory_store
 
+import gleam/result
+
+pub const bank_account_event_type = "BankAccountEvent"
+pub const bank_account_type = "BankAccount"
+
 pub type BankAccount {
-  BankAccount(opened: Bool, balance: Float)
+  BankAccount(balance: Float)
+  UnopenedBankAccount
 }
 
 pub type BankAccountCommand {
@@ -26,40 +32,50 @@ pub type BankAccountEvent {
   CustomerWithdrewCash(amount: Float, balance: Float)
 }
 
+
+pub type BankAccountError {
+  CantDepositNegativeAmount
+  CantOperateOnUnopenedAccount
+  CantWithdrawMoreThanCurrentBalance
+}
+
 pub fn handle(
   bank_account: BankAccount,
   command: BankAccountCommand,
-) -> Result(List(BankAccountEvent), Nil) {
-  case command {
-    OpenAccount(account_id) -> Ok([AccountOpened(account_id)])
-    DepositMoney(amount) -> {
-      let balance = bank_account.balance +. amount
+) -> Result(List(BankAccountEvent), BankAccountError) {
+  case bank_account, command {
+    UnopenedBankAccount, OpenAccount(account_id) ->
+      Ok([AccountOpened(account_id)])
+    BankAccount(balance), DepositMoney(amount) -> {
+      let balance = balance +. amount
       case amount >. 0.0 {
         True -> Ok([CustomerDepositedCash(amount:, balance:)])
-        False -> Error(Nil)
+        False -> Error(CantDepositNegativeAmount)
       }
     }
-    WithDrawMoney(amount) -> {
-      let balance = bank_account.balance -. amount
+    BankAccount(balance), WithDrawMoney(amount) -> {
+      let balance = balance -. amount
       case amount >. 0.0 && balance >. 0.0 {
         True -> Ok([CustomerWithdrewCash(amount:, balance:)])
-        False -> Error(Nil)
+        False -> Error(CantWithdrawMoreThanCurrentBalance)
       }
     }
+    _, _ -> Error(CantOperateOnUnopenedAccount)
   }
 }
 
 pub fn apply(bank_account: BankAccount, event: BankAccountEvent) {
-  case event {
-    AccountOpened(_) -> BankAccount(..bank_account, opened: True)
-    CustomerDepositedCash(_, balance) -> BankAccount(..bank_account, balance:)
-    CustomerWithdrewCash(_, balance) -> BankAccount(..bank_account, balance:)
+  case bank_account, event {
+    UnopenedBankAccount, AccountOpened(_) -> BankAccount(0.0)
+    BankAccount(_), CustomerDepositedCash(_, balance) -> BankAccount(balance:)
+    BankAccount(_), CustomerWithdrewCash(_, balance) -> BankAccount(balance:)
+    _, _ -> panic
   }
 }
 
 pub fn main() {
   let mem_store =
-    memory_store.new(BankAccount(opened: False, balance: 0.0), handle, apply)
+    memory_store.new(UnopenedBankAccount, handle, apply)
   let query = fn(
     aggregate_id: String,
     events: List(eventsourcing.EventEnvelop(BankAccountEvent)),

birdie_snapshots/load_aggregate_entity.accepted

@@ -4,4 +4,4 @@ title: load aggregate entity
 file: ./test/eventsourcing_test.gleam
 test_name: load_aggregate_entity_test
 ---
-Ok(BankAccount(True, 4.01))
+Ok(BankAccount(4.01))

gleam.toml

@@ -1,5 +1,5 @@
 name = "eventsourcing"
-version = "3.0.0"
+version = "3.0.1"
 
 # Fill out these fields if you intend to generate HTML documentation or publish
 # your project to the Hex package manager.

test/eventsourcing_test.gleam

@@ -13,7 +13,7 @@ pub fn main() {
 pub fn execute_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -30,7 +30,7 @@ pub fn execute_test() {
 pub fn query_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -57,7 +57,7 @@ pub fn query_test() {
 pub fn load_events_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -97,7 +97,7 @@ pub fn load_events_test() {
 pub fn load_events_with_metadata_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -122,7 +122,7 @@ pub fn load_events_with_metadata_test() {
 pub fn load_events_emtpy_aggregate_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -137,7 +137,7 @@ pub fn load_events_emtpy_aggregate_test() {
 pub fn load_aggregate_entity_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )
@@ -177,7 +177,7 @@ pub fn load_aggregate_entity_test() {
 pub fn load_emtpy_aggregate_entity_test() {
   let mem_store =
     memory_store.new(
-      example_bank_account.BankAccount(opened: False, balance: 0.0),
+      example_bank_account.UnopenedBankAccount,
       example_bank_account.handle,
       example_bank_account.apply,
     )

test/example_bank_account.gleam

@@ -4,7 +4,8 @@ import gleam/json
 import gleam/result
 
 pub type BankAccount {
-  BankAccount(opened: Bool, balance: Float)
+  BankAccount(balance: Float)
+  UnopenedBankAccount
 }
 
 pub const bank_account_type = "BankAccount"
@@ -23,34 +24,43 @@ pub type BankAccountEvent {
 
 pub const bank_account_event_type = "BankAccountEvent"
 
+pub type BankAccountError {
+  CantDepositNegativeAmount
+  CantOperateOnUnopenedAccount
+  CantWithdrawMoreThanCurrentBalance
+}
+
 pub fn handle(
   bank_account: BankAccount,
   command: BankAccountCommand,
-) -> Result(List(BankAccountEvent), Nil) {
-  case command {
-    OpenAccount(account_id) -> Ok([AccountOpened(account_id)])
-    DepositMoney(amount) -> {
-      let balance = bank_account.balance +. amount
+) -> Result(List(BankAccountEvent), BankAccountError) {
+  case bank_account, command {
+    UnopenedBankAccount, OpenAccount(account_id) ->
+      Ok([AccountOpened(account_id)])
+    BankAccount(balance), DepositMoney(amount) -> {
+      let balance = balance +. amount
       case amount >. 0.0 {
         True -> Ok([CustomerDepositedCash(amount:, balance:)])
-        False -> Error(Nil)
+        False -> Error(CantDepositNegativeAmount)
       }
     }
-    WithDrawMoney(amount) -> {
-      let balance = bank_account.balance -. amount
+    BankAccount(balance), WithDrawMoney(amount) -> {
+      let balance = balance -. amount
       case amount >. 0.0 && balance >. 0.0 {
         True -> Ok([CustomerWithdrewCash(amount:, balance:)])
-        False -> Error(Nil)
+        False -> Error(CantWithdrawMoreThanCurrentBalance)
       }
     }
+    _, _ -> Error(CantOperateOnUnopenedAccount)
   }
 }
 
 pub fn apply(bank_account: BankAccount, event: BankAccountEvent) {
-  case event {
-    AccountOpened(_) -> BankAccount(..bank_account, opened: True)
-    CustomerDepositedCash(_, balance) -> BankAccount(..bank_account, balance:)
-    CustomerWithdrewCash(_, balance) -> BankAccount(..bank_account, balance:)
+  case bank_account, event {
+    UnopenedBankAccount, AccountOpened(_) -> BankAccount(0.0)
+    BankAccount(_), CustomerDepositedCash(_, balance) -> BankAccount(balance:)
+    BankAccount(_), CustomerWithdrewCash(_, balance) -> BankAccount(balance:)
+    _, _ -> panic
   }
 }