atomicModifyMutVar# has incorrect type

this ticket

specifically, currently we only expose in ghc-prim

atomicModifyMutVar# :: MutVar# s a -> (a -> b) -> State# s -> (# State# s,c #)

is the type more like the following?

atomicModifyMutVar# :: MutVar# s a -> (a -> (#a,b #)) -> State# s -> (# State# s,b #)

looking at GHC.IOREF

atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b
atomicModifyIORef (IORef (STRef r#)) f = IO $ \s -> atomicModifyMutVar# r# f s

it seems that either way, something screwy is afoot

i'm not sure where the spurious c type variable comes from

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
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changed milestone to %8.2.1

changed weight to 5

added Tbug Trac import labels

There's a comment about this in compiler/prelude/primops.txt.pp. But it should be a Haddock comment so it shows up in the documentation. A note on why we don't use an unboxed tuple would also be nice.

mentioned in commit d91b1045

closed

Trac metadata

Trac field	Value
Resolution	Unresolved → ResolvedFixed

added Pnormal label