[Git][ghc/ghc][wip/jeltsch/system-io-uncovering] Move `MonadFix IO` instance declaration to `base`

24 Feb 2026

Wolfgang Jeltsch pushed to branch wip/jeltsch/system-io-uncovering at Glasgow Haskell Compiler / GHC


Commits:
f59b6261 by Wolfgang Jeltsch at 2026-02-24T16:47:45+02:00
Move `MonadFix IO` instance declaration to `base`

- - - - -


6 changed files:

- libraries/base/src/Control/Monad/Fix.hs
- libraries/ghc-internal/src/GHC/Internal/Control/Monad/Fix.hs
- testsuite/tests/interface-stability/base-exports.stdout
- testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
- testsuite/tests/interface-stability/base-exports.stdout-mingw32
- testsuite/tests/interface-stability/base-exports.stdout-ws-32


Changes:

=====================================
libraries/base/src/Control/Monad/Fix.hs
=====================================
@@ -119,3 +119,9 @@ module Control.Monad.Fix
      ) where
 
 import GHC.Internal.Control.Monad.Fix
+
+import GHC.Internal.System.IO
+
+-- | @since base-2.01
+instance MonadFix IO where
+    mfix = fixIO


=====================================
libraries/ghc-internal/src/GHC/Internal/Control/Monad/Fix.hs
=====================================
@@ -39,7 +39,6 @@ import GHC.Internal.Base ( Monad, errorWithoutStackTrace, (.) )
 import GHC.Internal.Generics
 import GHC.Internal.List ( head, drop )
 import GHC.Internal.Control.Monad.ST.Imp
-import GHC.Internal.System.IO
 
 -- | Monads having fixed points with a \'knot-tying\' semantics.
 -- Instances of 'MonadFix' should satisfy the following laws:
@@ -98,10 +97,6 @@ instance MonadFix NonEmpty where
       neHead ~(a :| _) = a
       neTail ~(_ :| as) = as

--- | @since base-2.01
-instance MonadFix IO where
-    mfix = fixIO
-
 -- | @since base-2.01
 instance MonadFix ((->) r) where
     mfix f = \ r -> let a = f a r in a


=====================================
testsuite/tests/interface-stability/base-exports.stdout
=====================================
@@ -11544,6 +11544,7 @@ instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fail.MonadFail f => GH
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.P -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.ReadP -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadPrec.ReadPrec -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadPrec’
+instance [safe] GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘Control.Monad.Fix’
 instance forall (f :: * -> *) (g :: * -> *). (GHC.Internal.Control.Monad.Fix.MonadFix f, GHC.Internal.Control.Monad.Fix.MonadFix g) => GHC.Internal.Control.Monad.Fix.MonadFix (f GHC.Internal.Generics.:*: g) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Semigroup.Internal.Alt f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Monoid.Ap f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
@@ -11552,7 +11553,6 @@ instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Semigroup.Int
 instance forall e. GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Either.Either e) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall r. GHC.Internal.Control.Monad.Fix.MonadFix ((->) r) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.First -- Defined in ‘GHC.Internal.Control.Monad.Fix’
-instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.Last -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix [] -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *) i (c :: GHC.Internal.Generics.Meta). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Generics.M1 i c f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
=====================================
@@ -11571,6 +11571,7 @@ instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fail.MonadFail f => GH
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.P -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.ReadP -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadPrec.ReadPrec -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadPrec’
+instance [safe] GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘Control.Monad.Fix’
 instance forall (f :: * -> *) (g :: * -> *). (GHC.Internal.Control.Monad.Fix.MonadFix f, GHC.Internal.Control.Monad.Fix.MonadFix g) => GHC.Internal.Control.Monad.Fix.MonadFix (f GHC.Internal.Generics.:*: g) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Semigroup.Internal.Alt f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Monoid.Ap f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
@@ -11579,7 +11580,6 @@ instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Semigroup.Int
 instance forall e. GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Either.Either e) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall r. GHC.Internal.Control.Monad.Fix.MonadFix ((->) r) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.First -- Defined in ‘GHC.Internal.Control.Monad.Fix’
-instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.Last -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix [] -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *) i (c :: GHC.Internal.Generics.Meta). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Generics.M1 i c f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-mingw32
=====================================
@@ -11802,6 +11802,7 @@ instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fail.MonadFail f => GH
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.P -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.ReadP -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadPrec.ReadPrec -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadPrec’
+instance [safe] GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘Control.Monad.Fix’
 instance forall (f :: * -> *) (g :: * -> *). (GHC.Internal.Control.Monad.Fix.MonadFix f, GHC.Internal.Control.Monad.Fix.MonadFix g) => GHC.Internal.Control.Monad.Fix.MonadFix (f GHC.Internal.Generics.:*: g) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Semigroup.Internal.Alt f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Monoid.Ap f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
@@ -11810,7 +11811,6 @@ instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Semigroup.Int
 instance forall e. GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Either.Either e) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall r. GHC.Internal.Control.Monad.Fix.MonadFix ((->) r) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.First -- Defined in ‘GHC.Internal.Control.Monad.Fix’
-instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.Last -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix [] -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *) i (c :: GHC.Internal.Generics.Meta). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Generics.M1 i c f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-ws-32
=====================================
@@ -11544,6 +11544,7 @@ instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fail.MonadFail f => GH
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.P -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadP.ReadP -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadP’
 instance GHC.Internal.Control.Monad.Fail.MonadFail GHC.Internal.Text.ParserCombinators.ReadPrec.ReadPrec -- Defined in ‘GHC.Internal.Text.ParserCombinators.ReadPrec’
+instance [safe] GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘Control.Monad.Fix’
 instance forall (f :: * -> *) (g :: * -> *). (GHC.Internal.Control.Monad.Fix.MonadFix f, GHC.Internal.Control.Monad.Fix.MonadFix g) => GHC.Internal.Control.Monad.Fix.MonadFix (f GHC.Internal.Generics.:*: g) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Semigroup.Internal.Alt f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Monoid.Ap f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
@@ -11552,7 +11553,6 @@ instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Semigroup.Int
 instance forall e. GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Data.Either.Either e) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall r. GHC.Internal.Control.Monad.Fix.MonadFix ((->) r) -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.First -- Defined in ‘GHC.Internal.Control.Monad.Fix’
-instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Types.IO -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix GHC.Internal.Data.Monoid.Last -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance GHC.Internal.Control.Monad.Fix.MonadFix [] -- Defined in ‘GHC.Internal.Control.Monad.Fix’
 instance forall (f :: * -> *) i (c :: GHC.Internal.Generics.Meta). GHC.Internal.Control.Monad.Fix.MonadFix f => GHC.Internal.Control.Monad.Fix.MonadFix (GHC.Internal.Generics.M1 i c f) -- Defined in ‘GHC.Internal.Control.Monad.Fix’



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/f59b62611d826b0b1cdc396a9b349a82...

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[Git][ghc/ghc][wip/jeltsch/system-io-uncovering] Move `MonadFix IO` instance declaration to `base`

Wolfgang Jeltsch (＠jeltsch)