erlang: fib_server.erl, 5/5 classic programs (+8 tests)

lib/erlang/tests/programs/fib_server.sx

@@ -0,0 +1,152 @@
+;; Fib server — long-lived process that computes fibonacci numbers on
+;; request. Tests recursive function evaluation inside a server loop.
+
+(define er-fib-test-count 0)
+(define er-fib-test-pass 0)
+(define er-fib-test-fails (list))
+
+(define
+  er-fib-test
+  (fn
+    (name actual expected)
+    (set! er-fib-test-count (+ er-fib-test-count 1))
+    (if
+      (= actual expected)
+      (set! er-fib-test-pass (+ er-fib-test-pass 1))
+      (append! er-fib-test-fails {:actual actual :expected expected :name name}))))
+
+(define fib-ev erlang-eval-ast)
+
+;; Fib + server-loop source. Standalone so each test can chain queries.
+(define
+  er-fib-server-src
+  "Fib = fun (0) -> 0; (1) -> 1; (N) -> Fib(N-1) + Fib(N-2) end,
+   FibSrv = fun () ->
+     Loop = fun () ->
+       receive
+         {fib, N, From} -> From ! Fib(N), Loop();
+         stop -> ok
+       end
+     end,
+     Loop()
+   end")
+
+;; Base cases.
+(er-fib-test
+  "fib(0)"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 0, Me},
+       receive R -> Srv ! stop, R end"))
+  0)
+
+(er-fib-test
+  "fib(1)"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 1, Me},
+       receive R -> Srv ! stop, R end"))
+  1)
+
+;; Larger values.
+(er-fib-test
+  "fib(10) = 55"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 10, Me},
+       receive R -> Srv ! stop, R end"))
+  55)
+
+(er-fib-test
+  "fib(15) = 610"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 15, Me},
+       receive R -> Srv ! stop, R end"))
+  610)
+
+;; Multiple sequential queries to one server. Sum to avoid dict-equality.
+(er-fib-test
+  "sequential fib(5..8) sum"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 5, Me}, A = receive Ra -> Ra end,
+       Srv ! {fib, 6, Me}, B = receive Rb -> Rb end,
+       Srv ! {fib, 7, Me}, C = receive Rc -> Rc end,
+       Srv ! {fib, 8, Me}, D = receive Rd -> Rd end,
+       Srv ! stop,
+       A + B + C + D"))
+  47)
+
+;; Verify Fib obeys the recurrence — fib(n) = fib(n-1) + fib(n-2).
+(er-fib-test
+  "fib recurrence at n=12"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Srv ! {fib, 10, Me}, A = receive Ra -> Ra end,
+       Srv ! {fib, 11, Me}, B = receive Rb -> Rb end,
+       Srv ! {fib, 12, Me}, C = receive Rc -> Rc end,
+       Srv ! stop,
+       C - (A + B)"))
+  0)
+
+;; Two clients each get their own answer; main sums the results.
+(er-fib-test
+  "two clients sum"
+  (fib-ev
+    (str
+      er-fib-server-src
+      ", Me = self(),
+       Srv = spawn(FibSrv),
+       Client = fun (N) ->
+         spawn(fun () ->
+           Srv ! {fib, N, self()},
+           receive R -> Me ! {result, R} end
+         end)
+       end,
+       Client(7),
+       Client(9),
+       {result, A} = receive M1 -> M1 end,
+       {result, B} = receive M2 -> M2 end,
+       Srv ! stop,
+       A + B"))
+  47)
+
+;; Trace queries via io-buffer.
+(er-fib-test
+  "trace fib 0..6"
+  (do
+    (er-io-flush!)
+    (fib-ev
+      (str
+        er-fib-server-src
+        ", Me = self(),
+         Srv = spawn(FibSrv),
+         Ask = fun (N) -> Srv ! {fib, N, Me}, receive R -> io:format(\"~p \", [R]) end end,
+         Ask(0), Ask(1), Ask(2), Ask(3), Ask(4), Ask(5), Ask(6),
+         Srv ! stop,
+         done"))
+    (er-io-buffer-content))
+  "0 1 1 2 3 5 8 ")
+
+(define
+  er-fib-test-summary
+  (str "fib " er-fib-test-pass "/" er-fib-test-count))

plans/erlang-on-sx.md

@@ -74,7 +74,7 @@ Core mapping:
   - [x] `ping_pong.erl` — two processes exchanging messages — **4 ping-pong tests**
   - [x] `bank.erl` — account server (deposit/withdraw/balance) — **8 bank tests**
   - [x] `echo.erl` — minimal server — **7 echo tests**
-  - [ ] `fib_server.erl` — compute fib on request
+  - [x] `fib_server.erl` — compute fib on request — **8 fib tests**
 - [ ] `lib/erlang/conformance.sh` + runner, `scoreboard.json` + `scoreboard.md`
 - [ ] Target: 5/5 classic programs + 1M-process ring benchmark runs
 
@@ -99,6 +99,7 @@ Core mapping:
 
 _Newest first._
 
+- **2026-04-25 fib_server.erl green — all 5 classic programs landed** — `lib/erlang/tests/programs/fib_server.sx` with 8 tests. Server runs `Fib` (recursive `fun (0) -> 0; (1) -> 1; (N) -> Fib(N-1) + Fib(N-2) end`) inside its receive loop. Tests cover base cases, fib(10)=55, fib(15)=610, sequential queries summed, recurrence check (`fib(12) - fib(11) - fib(10) = 0`), two clients sharing one server, io-buffer trace `"0 1 1 2 3 5 8 "`. Total suite 358/358. Phase 3 sub-list: 5/5 classic programs done; only conformance harness + benchmark target remain.
 - **2026-04-25 echo.erl green** — `lib/erlang/tests/programs/echo.sx` with 7 tests. Server: `receive {From, Msg} -> From ! Msg, Loop(); stop -> ok end`. Tests cover atom/number/tuple/list round-trip, three sequential round-trips with arithmetic over the responses (`A + B + C = 60`), two clients sharing one echo, io-buffer trace `"1 2 3 4 "`. Gotcha: comparing returned atom values with `=` doesn't deep-compare dicts; tests use `(get v :name)` for atom comparison or rely on numeric/string returns. Total suite 350/350.
 - **2026-04-24 bank.erl green** — `lib/erlang/tests/programs/bank.sx` with 8 tests. Stateful server pattern: `Server = fun (Balance) -> receive ... Server(NewBalance) end end` recursively threads balance through each iteration. Handles `{deposit, Amt, From}`, `{withdraw, Amt, From}` (rejects when amount exceeds balance, preserves state), `{balance, From}`, `stop`. Tests cover deposit accumulation, withdrawal within balance, insufficient funds with state preservation, mixed transactions, clean shutdown, two-client interleave. Total suite 343/343.
 - **2026-04-24 ping_pong.erl green** — `lib/erlang/tests/programs/ping_pong.sx` with 4 tests: classic Pong server + Ping client with separate `ping_done`/`pong_done` notifications, 5-round trace via io-buffer (`"ppppp"`), main-as-pinger-4-rounds (no intermediate Ping proc), tagged-id round-trip (`"4 3 2 1 "`). All driven by `Ping = fun (Target, K) -> ... Ping(Target, K-1) ... end` self-recursion — captured-env reference works because `Ping` binds in main's mutable env before any spawned body looks it up. Total suite 335/335.