erlang: bank.erl account server (+8 tests)

lib/erlang/tests/programs/bank.sx

@@ -0,0 +1,159 @@
+;; Bank account server — stateful process, balance threaded through
+;; recursive loop. Handles {deposit, Amt, From}, {withdraw, Amt, From},
+;; {balance, From}, stop. Tests stateful process patterns.
+
+(define er-bank-test-count 0)
+(define er-bank-test-pass 0)
+(define er-bank-test-fails (list))
+
+(define
+  er-bank-test
+  (fn
+    (name actual expected)
+    (set! er-bank-test-count (+ er-bank-test-count 1))
+    (if
+      (= actual expected)
+      (set! er-bank-test-pass (+ er-bank-test-pass 1))
+      (append! er-bank-test-fails {:actual actual :expected expected :name name}))))
+
+(define bank-ev erlang-eval-ast)
+
+;; Server fun shared by all tests — threaded via the program string.
+(define
+  er-bank-server-src
+  "Server = fun (Balance) ->
+     receive
+       {deposit, Amt, From} -> From ! ok, Server(Balance + Amt);
+       {withdraw, Amt, From} ->
+         if Amt > Balance -> From ! insufficient, Server(Balance);
+            true -> From ! ok, Server(Balance - Amt)
+         end;
+       {balance, From} -> From ! Balance, Server(Balance);
+       stop -> ok
+     end
+   end")
+
+;; Open account, deposit, check balance.
+(er-bank-test
+  "deposit 100 -> balance 100"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(0) end),
+       Bank ! {deposit, 100, Me},
+       receive ok -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  100)
+
+;; Multiple deposits accumulate.
+(er-bank-test
+  "deposits accumulate"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(0) end),
+       Bank ! {deposit, 50, Me}, receive ok -> ok end,
+       Bank ! {deposit, 25, Me}, receive ok -> ok end,
+       Bank ! {deposit, 10, Me}, receive ok -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  85)
+
+;; Withdraw within balance succeeds; insufficient gets rejected.
+(er-bank-test
+  "withdraw within balance"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(100) end),
+       Bank ! {withdraw, 30, Me}, receive ok -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  70)
+
+(er-bank-test
+  "withdraw insufficient"
+  (get
+    (bank-ev
+      (str
+        er-bank-server-src
+        ", Me = self(),
+         Bank = spawn(fun () -> Server(20) end),
+         Bank ! {withdraw, 100, Me},
+         receive R -> Bank ! stop, R end"))
+    :name)
+  "insufficient")
+
+;; State preserved across an insufficient withdrawal.
+(er-bank-test
+  "state preserved on rejection"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(50) end),
+       Bank ! {withdraw, 1000, Me}, receive _ -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  50)
+
+;; Mixed deposits and withdrawals.
+(er-bank-test
+  "mixed transactions"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(100) end),
+       Bank ! {deposit, 50, Me}, receive ok -> ok end,
+       Bank ! {withdraw, 30, Me}, receive ok -> ok end,
+       Bank ! {deposit, 10, Me}, receive ok -> ok end,
+       Bank ! {withdraw, 5, Me}, receive ok -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  125)
+
+;; Server.stop terminates the bank cleanly — main can verify by
+;; sending stop and then exiting normally.
+(er-bank-test
+  "server stops cleanly"
+  (get
+    (bank-ev
+      (str
+        er-bank-server-src
+        ", Me = self(),
+         Bank = spawn(fun () -> Server(0) end),
+         Bank ! stop,
+         done"))
+    :name)
+  "done")
+
+;; Two clients sharing one bank — interleaved transactions.
+(er-bank-test
+  "two clients share bank"
+  (bank-ev
+    (str
+      er-bank-server-src
+      ", Me = self(),
+       Bank = spawn(fun () -> Server(0) end),
+       Client = fun (Amt) ->
+         spawn(fun () ->
+           Bank ! {deposit, Amt, self()},
+           receive ok -> Me ! deposited end
+         end)
+       end,
+       Client(40),
+       Client(60),
+       receive deposited -> ok end,
+       receive deposited -> ok end,
+       Bank ! {balance, Me},
+       receive B -> Bank ! stop, B end"))
+  100)
+
+(define
+  er-bank-test-summary
+  (str "bank " er-bank-test-pass "/" er-bank-test-count))