cl: Phase 3 classic programs — restart-demo (7 tests) + parse-recover (6 tests)

restart-demo.sx: safe-divide with division-by-zero condition, use-zero
and retry restarts. Demonstrates handler-bind invoking a restart to
resume computation with a corrected value.

parse-recover.sx: token parser signalling parse-error on non-integer
tokens, skip-token and use-zero restarts. Demonstrates recovery-via-
restart and handler-case abort patterns.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/common-lisp/tests/programs/restart-demo.sx

@@ -0,0 +1,141 @@
+;; restart-demo.sx — Classic CL condition system demo
+;;
+;; Demonstrates resumable exceptions via restarts.
+;; The `safe-divide` function signals a division-by-zero condition
+;; and offers two restarts:
+;;   :use-zero  — return 0 as the result
+;;   :retry     — call safe-divide again with a corrected divisor
+;;
+;; Depends on: lib/common-lisp/runtime.sx already loaded.
+
+;; ── safe-divide ────────────────────────────────────────────────────────────
+;;
+;; Divides numerator by denominator.
+;; When denominator is 0, signals division-by-zero with two restarts.
+
+(define
+  safe-divide
+  (fn
+    (n d)
+    (if
+      (= d 0)
+      (cl-restart-case
+        (fn
+          ()
+          (cl-signal
+            (cl-make-condition
+              "division-by-zero"
+              "operation"
+              "/"
+              "operands"
+              (list n d)))
+          (error "division by zero — no restart invoked"))
+        (list "use-zero" (list) (fn () 0))
+        (list "retry" (list "d") (fn (d2) (safe-divide n d2))))
+      (/ n d))))
+
+;; ── tests ─────────────────────────────────────────────────────────────────
+
+(define passed 0)
+(define failed 0)
+(define failures (list))
+
+(define
+  check
+  (fn
+    (label got expected)
+    (if
+      (= got expected)
+      (set! passed (+ passed 1))
+      (begin
+        (set! failed (+ failed 1))
+        (set!
+          failures
+          (append
+            failures
+            (list
+              (str
+                "FAIL ["
+                label
+                "]: got="
+                (inspect got)
+                " expected="
+                (inspect expected)))))))))
+
+(define
+  reset-stacks!
+  (fn () (set! cl-handler-stack (list)) (set! cl-restart-stack (list))))
+
+;; Normal division
+(reset-stacks!)
+(check "10 / 2 = 5" (safe-divide 10 2) 5)
+
+;; Invoke use-zero restart
+(reset-stacks!)
+(check
+  "10 / 0 -> use-zero"
+  (cl-handler-bind
+    (list
+      (list "division-by-zero" (fn (c) (cl-invoke-restart "use-zero"))))
+    (fn () (safe-divide 10 0)))
+  0)
+
+;; Invoke retry restart with a corrected denominator
+(reset-stacks!)
+(check
+  "10 / 0 -> retry with 2"
+  (cl-handler-bind
+    (list
+      (list
+        "division-by-zero"
+        (fn (c) (cl-invoke-restart "retry" 2))))
+    (fn () (safe-divide 10 0)))
+  5)
+
+;; Nested calls: outer handles the inner divide-by-zero
+(reset-stacks!)
+(check
+  "nested: 20 / (0->4) = 5"
+  (cl-handler-bind
+    (list
+      (list
+        "division-by-zero"
+        (fn (c) (cl-invoke-restart "retry" 4))))
+    (fn () (let ((r1 (safe-divide 20 0))) r1)))
+  5)
+
+;; handler-case — unwinding version
+(reset-stacks!)
+(check
+  "handler-case: catches division-by-zero"
+  (cl-handler-case
+    (fn () (safe-divide 9 0))
+    (list "division-by-zero" (fn (c) "caught!")))
+  "caught!")
+
+;; Verify use-zero is idempotent (two uses)
+(reset-stacks!)
+(check
+  "two use-zero invocations"
+  (cl-handler-bind
+    (list
+      (list "division-by-zero" (fn (c) (cl-invoke-restart "use-zero"))))
+    (fn
+      ()
+      (+
+        (safe-divide 10 0)
+        (safe-divide 3 0))))
+  0)
+
+;; No restart needed for normal division
+(reset-stacks!)
+(check
+  "no restart needed for 8/4"
+  (safe-divide 8 4)
+  2)
+
+;; ── summary ────────────────────────────────────────────────────────────────
+
+(define demo-passed passed)
+(define demo-failed failed)
+(define demo-failures failures)