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refcount: define macro-constraint HasCallStackIfDebug #495

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Dec 11, 2024
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refcount: define macro-constraint HasCallStackIfDebug #495

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14 changes: 7 additions & 7 deletions src-control/Control/RefCount.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -200,9 +200,9 @@ class RefCounted obj where
getRefCounter :: obj -> RefCounter (FinaliserM obj)

#ifdef NO_IGNORE_ASSERTS
#define HAS_CALL_STACK => HasCallStack
#define HasCallStackIfDebug HasCallStack
#else
#define HAS_CALL_STACK
#define HasCallStackIfDebug ()
#endif
Comment on lines 202 to 206
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I prefer the all-caps macros because it makes it clear that it is not actual haskell syntax

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Do you feel that with the all-caps name, this is an improvement?

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There is, of course, the risk that this is highly dependent on what is arguably a GHC bug.


-- GHC says specialising is too complicated! But it's ok, each of these can
Expand All @@ -219,7 +219,7 @@ class RefCounted obj where
--
newRef ::
(RefCounted obj, FinaliserM obj ~ m, PrimMonad m)
HAS_CALL_STACK
=> HasCallStackIfDebug
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What's the reason that this does not throw a warning?

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By the looks of it, GHC combines successive constraint arrows, so by the time it reaches the warning subsystem, (A, B) => () => x has turned into (A, B) => x by concatenation, whereas it does no other normalisation, so (A, B, ()) => x remains unchanged.

=> m ()
-> (RefCounter m -> obj)
-> m (Ref obj)
Expand All @@ -234,7 +234,7 @@ newRef finaliser mkObject = do
--
releaseRef ::
(RefCounted obj, FinaliserM obj ~ m, PrimMonad m, MonadMask m)
HAS_CALL_STACK
=> HasCallStackIfDebug
=> Ref obj
-> m ()
releaseRef ref@Ref{refobj} = do
Expand Down Expand Up @@ -268,7 +268,7 @@ deRef ref@Ref{refobj} =
withRef ::
forall m obj a.
PrimMonad m
HAS_CALL_STACK
=> HasCallStackIfDebug
=> Ref obj
-> (obj -> m a)
-> m a
Expand All @@ -280,7 +280,7 @@ withRef ref@Ref{refobj} f = do
--
dupRef ::
(RefCounted obj, FinaliserM obj ~ m, PrimMonad m)
HAS_CALL_STACK
=> HasCallStackIfDebug
=> Ref obj
-> m (Ref obj)
dupRef ref@Ref{refobj} = do
Expand Down Expand Up @@ -313,7 +313,7 @@ mkWeakRefFromRaw obj = WeakRef obj
--
deRefWeak ::
(RefCounted obj, FinaliserM obj ~ m, PrimMonad m)
HAS_CALL_STACK
=> HasCallStackIfDebug
=> WeakRef obj
-> m (Maybe (Ref obj))
deRefWeak (WeakRef obj) = do
Expand Down
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