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rose-ash/lib/haskell/tests/program-safediv.sx
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haskell: Phase 16 — exception handling (catch/try/throwIO/evaluate/handle/throw)
hk-bind-exceptions! in eval.sx registers throwIO, throw, evaluate, catch,
try, handle, displayException. SomeException constructor pre-registered
in runtime.sx (arity 1, type SomeException).

throwIO and the existing error primitive both raise via SX `raise` with a
uniform "hk-error: msg" string. catch/try/handle parse it back into a
SomeException via hk-exception-of, which strips nested
'Unhandled exception: "..."' host wraps (CEK's host_error formatter) and
the "hk-error: " prefix.

catch and handle evaluate the handler outside the guard scope (build an
"ok"/"exn" outcome tag inside guard, then dispatch outside) so that a
re-throw from the handler propagates past this catch — matching Haskell
semantics rather than infinite-looping in the same guard.

14 unit tests in tests/exceptions.sx (catch success, catch error, try
Right/Left, handle, throwIO + catch/try, evaluate, nested catch, do-bind
through catch, branch on try result, IORef-mutating handler).

Conformance: safediv.hs (8/8) and trycatch.hs (8/8). Scoreboard now
285/285 tests, 36/36 programs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
2026-05-08 00:17:46 +00:00

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;; safediv.hs — safe division using catch (Phase 16 conformance).
(define
hk-safediv-source
"safeDiv :: Int -> Int -> IO Int
safeDiv _ 0 = throwIO (SomeException \"division by zero\")
safeDiv x y = return (x `div` y)
guarded :: Int -> Int -> IO Int
guarded x y = catch (safeDiv x y) (\\(SomeException _) -> return 0)
reason :: Int -> Int -> IO String
reason x y = catch (safeDiv x y `seq` return \"ok\")
(\\(SomeException m) -> return m)
bothBranches :: Int -> Int -> IO Int
bothBranches x y = do
v <- catch (safeDiv x y) (\\(SomeException _) -> return (-1))
return (v + 100)
")
(hk-test
"safediv.hs — divide by non-zero"
(hk-deep-force
(hk-run
(str hk-safediv-source "main = guarded 10 2")))
(list "IO" 5))
(hk-test
"safediv.hs — divide by zero returns 0"
(hk-deep-force
(hk-run
(str hk-safediv-source "main = guarded 10 0")))
(list "IO" 0))
(hk-test
"safediv.hs — divide by zero — reason captured"
(hk-deep-force
(hk-run
(str hk-safediv-source "main = catch (safeDiv 1 0) (\\(SomeException m) -> return 0) >> reason 1 0")))
(list "IO" "division by zero"))
(hk-test
"safediv.hs — bothBranches success path"
(hk-deep-force
(hk-run
(str hk-safediv-source "main = bothBranches 8 2")))
(list "IO" 104))
(hk-test
"safediv.hs — bothBranches failure path"
(hk-deep-force
(hk-run
(str hk-safediv-source "main = bothBranches 8 0")))
(list "IO" 99))
(hk-test
"safediv.hs — chained safeDiv with catch"
(hk-deep-force
(hk-run
(str hk-safediv-source
"main = do { a <- guarded 20 4; b <- guarded 7 0; return (a + b) }")))
(list "IO" 5))
(hk-test
"safediv.hs — try then bind through Either"
(hk-deep-force
(hk-run
(str hk-safediv-source
"main = do { r <- try (safeDiv 1 0); case r of { Right v -> return v; Left (SomeException m) -> return 999 } }")))
(list "IO" 999))
(hk-test
"safediv.hs — handle (flip catch)"
(hk-deep-force
(hk-run
(str hk-safediv-source
"main = handle (\\(SomeException _) -> return 0) (safeDiv 5 0)")))
(list "IO" 0))