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/parse-recover.sx

@@ -0,0 +1,163 @@
+;; parse-recover.sx — Parser with skipped-token restart
+;;
+;; Classic CL pattern: a simple token parser that signals a condition
+;; when it encounters an unexpected token. The :skip-token restart
+;; allows the parser to continue past the offending token.
+;;
+;; Depends on: lib/common-lisp/runtime.sx already loaded.
+
+;; ── condition type ─────────────────────────────────────────────────────────
+
+(cl-define-condition "parse-error" (list "error") (list "token" "position"))
+
+;; ── simple token parser ────────────────────────────────────────────────────
+;;
+;; parse-numbers: given a list of tokens (strings), parse integers.
+;; Non-integer tokens signal parse-error with two restarts:
+;;   skip-token   — skip the bad token and continue
+;;   use-zero     — use 0 in place of the bad token
+
+(define
+  parse-numbers
+  (fn
+    (tokens)
+    (define result (list))
+    (define
+      process
+      (fn
+        (toks)
+        (if
+          (empty? toks)
+          result
+          (let
+            ((tok (first toks)) (rest-toks (rest toks)))
+            (let
+              ((n (string->number tok 10)))
+              (if
+                n
+                (begin
+                  (set! result (append result (list n)))
+                  (process rest-toks))
+                (cl-restart-case
+                  (fn
+                    ()
+                    (cl-signal
+                      (cl-make-condition
+                        "parse-error"
+                        "token"
+                        tok
+                        "position"
+                        (len result)))
+                    (set! result (append result (list 0)))
+                    (process rest-toks))
+                  (list "skip-token" (list) (fn () (process rest-toks)))
+                  (list
+                    "use-zero"
+                    (list)
+                    (fn
+                      ()
+                      (begin
+                        (set! result (append result (list 0)))
+                        (process rest-toks)))))))))))
+    (process tokens)
+    result))
+
+;; ── 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))))
+
+;; All valid tokens
+(reset-stacks!)
+(check
+  "all valid: 1 2 3"
+  (cl-handler-bind
+    (list (list "parse-error" (fn (c) (cl-invoke-restart "skip-token"))))
+    (fn () (parse-numbers (list "1" "2" "3"))))
+  (list 1 2 3))
+
+;; Skip bad token
+(reset-stacks!)
+(check
+  "skip bad token: 1 x 3 -> (1 3)"
+  (cl-handler-bind
+    (list (list "parse-error" (fn (c) (cl-invoke-restart "skip-token"))))
+    (fn () (parse-numbers (list "1" "x" "3"))))
+  (list 1 3))
+
+;; Use zero for bad token
+(reset-stacks!)
+(check
+  "use-zero for bad: 1 x 3 -> (1 0 3)"
+  (cl-handler-bind
+    (list (list "parse-error" (fn (c) (cl-invoke-restart "use-zero"))))
+    (fn () (parse-numbers (list "1" "x" "3"))))
+  (list 1 0 3))
+
+;; Multiple bad tokens, all skipped
+(reset-stacks!)
+(check
+  "skip multiple bad: a 2 b 4 -> (2 4)"
+  (cl-handler-bind
+    (list (list "parse-error" (fn (c) (cl-invoke-restart "skip-token"))))
+    (fn () (parse-numbers (list "a" "2" "b" "4"))))
+  (list 2 4))
+
+;; handler-case: abort on first bad token
+(reset-stacks!)
+(check
+  "handler-case: abort on first bad"
+  (cl-handler-case
+    (fn () (parse-numbers (list "1" "bad" "3")))
+    (list
+      "parse-error"
+      (fn
+        (c)
+        (str
+          "parse error at position "
+          (cl-condition-slot c "position")
+          ": "
+          (cl-condition-slot c "token")))))
+  "parse error at position 1: bad")
+
+;; Verify condition type hierarchy
+(reset-stacks!)
+(check
+  "parse-error isa error"
+  (cl-condition-of-type?
+    (cl-make-condition "parse-error" "token" "x" "position" 0)
+    "error")
+  true)
+
+;; ── summary ────────────────────────────────────────────────────────────────
+
+(define parse-passed passed)
+(define parse-failed failed)
+(define parse-failures failures)