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Use smart insertion and deletion in alterF #289

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Use smart insertion and deletion in alterF #289

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14 changes: 10 additions & 4 deletions Data/HashMap/Internal.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -1305,10 +1305,16 @@ alterF :: (Functor f, Eq k, Hashable k)
alterF f = \ !k !m ->
let
!h = hash k
mv = lookup' h k m
in (<$> f mv) $ \case
Nothing -> maybe m (const (delete' h k m)) mv
Just v' -> insert' h k v' m
lookupRes = lookupRecordCollision h k m
mv = lookupResToMaybe lookupRes
in (<$> f mv) $ \fres ->
case fres of
Nothing -> case lookupRes of
Absent -> m
Present _ i -> deleteKeyExists i h k m
Just v' -> case lookupRes of
Absent -> insertNewKey h k v' m
Present _ i -> insertKeyExists i h k v' m

-- We unconditionally rewrite alterF in RULES, but we expose an
-- unfolding just in case it's used in some way that prevents the
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