giles
ab66b29a74
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>
141 lines
3.6 KiB
Plaintext
141 lines
3.6 KiB
Plaintext
;; restart-demo.sx — Classic CL condition system demo
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;;
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;; Demonstrates resumable exceptions via restarts.
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;; The `safe-divide` function signals a division-by-zero condition
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;; and offers two restarts:
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;; :use-zero — return 0 as the result
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;; :retry — call safe-divide again with a corrected divisor
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;;
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;; Depends on: lib/common-lisp/runtime.sx already loaded.
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;; ── safe-divide ────────────────────────────────────────────────────────────
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;;
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;; Divides numerator by denominator.
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;; When denominator is 0, signals division-by-zero with two restarts.
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(define
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safe-divide
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(fn
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(n d)
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(if
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(= d 0)
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(cl-restart-case
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(fn
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()
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(cl-signal
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(cl-make-condition
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"division-by-zero"
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"operation"
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"/"
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"operands"
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(list n d)))
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(error "division by zero — no restart invoked"))
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(list "use-zero" (list) (fn () 0))
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(list "retry" (list "d") (fn (d2) (safe-divide n d2))))
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(/ n d))))
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;; ── tests ─────────────────────────────────────────────────────────────────
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(define passed 0)
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(define failed 0)
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(define failures (list))
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(define
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check
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(fn
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(label got expected)
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(if
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(= got expected)
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(set! passed (+ passed 1))
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(begin
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(set! failed (+ failed 1))
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(set!
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failures
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(append
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failures
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(list
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(str
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"FAIL ["
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label
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"]: got="
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(inspect got)
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" expected="
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(inspect expected)))))))))
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(define
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reset-stacks!
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(fn () (set! cl-handler-stack (list)) (set! cl-restart-stack (list))))
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;; Normal division
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(reset-stacks!)
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(check "10 / 2 = 5" (safe-divide 10 2) 5)
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;; Invoke use-zero restart
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(reset-stacks!)
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(check
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"10 / 0 -> use-zero"
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(cl-handler-bind
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(list
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(list "division-by-zero" (fn (c) (cl-invoke-restart "use-zero"))))
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(fn () (safe-divide 10 0)))
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0)
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;; Invoke retry restart with a corrected denominator
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(reset-stacks!)
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(check
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"10 / 0 -> retry with 2"
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(cl-handler-bind
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(list
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(list
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"division-by-zero"
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(fn (c) (cl-invoke-restart "retry" 2))))
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(fn () (safe-divide 10 0)))
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5)
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;; Nested calls: outer handles the inner divide-by-zero
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(reset-stacks!)
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(check
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"nested: 20 / (0->4) = 5"
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(cl-handler-bind
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(list
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(list
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"division-by-zero"
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(fn (c) (cl-invoke-restart "retry" 4))))
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(fn () (let ((r1 (safe-divide 20 0))) r1)))
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5)
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;; handler-case — unwinding version
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(reset-stacks!)
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(check
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"handler-case: catches division-by-zero"
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(cl-handler-case
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(fn () (safe-divide 9 0))
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(list "division-by-zero" (fn (c) "caught!")))
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"caught!")
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;; Verify use-zero is idempotent (two uses)
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(reset-stacks!)
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(check
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"two use-zero invocations"
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(cl-handler-bind
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(list
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(list "division-by-zero" (fn (c) (cl-invoke-restart "use-zero"))))
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(fn
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()
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(+
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(safe-divide 10 0)
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(safe-divide 3 0))))
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0)
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;; No restart needed for normal division
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(reset-stacks!)
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(check
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"no restart needed for 8/4"
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(safe-divide 8 4)
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2)
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;; ── summary ────────────────────────────────────────────────────────────────
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(define demo-passed passed)
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(define demo-failed failed)
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(define demo-failures failures) |