[Git][ghc/ghc][wip/jeltsch/text-read-uncovering] Move the implementation of `readConstr` into `base`

8 Apr 2026

Wolfgang Jeltsch pushed to branch wip/jeltsch/text-read-uncovering at Glasgow Haskell Compiler / GHC


Commits:
d70ced06 by Wolfgang Jeltsch at 2026-04-08T16:46:51+03:00
Move the implementation of `readConstr` into `base`

- - - - -


6 changed files:

- libraries/base/src/Data/Data.hs
- libraries/ghc-internal/src/GHC/Internal/Data/Data.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/Data/Data.hs
=====================================
@@ -99,3 +99,38 @@ module Data.Data (
 
 import GHC.Internal.Data.Data
 import Data.Typeable
+
+import GHC.Real (toRational)
+import GHC.Float (Double)
+import Data.Eq ((==))
+import Data.Function ((.))
+import Data.Maybe (Maybe (Nothing, Just))
+import Data.List (filter)
+import Data.String (String)
+import Text.Read (Read, reads)
+
+-- | Lookup a constructor via a string
+readConstr :: DataType -> String -> Maybe Constr
+readConstr dt str =
+      case dataTypeRep dt of
+        AlgRep cons -> idx cons
+        IntRep      -> mkReadCon (\i -> (mkPrimCon dt str (IntConstr i)))
+        FloatRep    -> mkReadCon ffloat
+        CharRep     -> mkReadCon (\c -> (mkPrimCon dt str (CharConstr c)))
+        NoRep       -> Nothing
+  where
+
+    -- Read a value and build a constructor
+    mkReadCon :: Read t => (t -> Constr) -> Maybe Constr
+    mkReadCon f = case (reads str) of
+                    [(t,"")] -> Just (f t)
+                    _ -> Nothing
+
+    -- Traverse list of algebraic datatype constructors
+    idx :: [Constr] -> Maybe Constr
+    idx cons = case filter ((==) str . showConstr) cons of
+                [] -> Nothing
+                hd : _ -> Just hd
+
+    ffloat :: Double -> Constr
+    ffloat =  mkPrimCon dt str . FloatConstr . toRational


=====================================
libraries/ghc-internal/src/GHC/Internal/Data/Data.hs
=====================================
@@ -61,6 +61,7 @@ module GHC.Internal.Data.Data (
         mkIntType,
         mkFloatType,
         mkCharType,
+        mkPrimCon,
         mkNoRepType,
         -- ** Observers
         dataTypeName,
@@ -94,7 +95,6 @@ module GHC.Internal.Data.Data (
         constrIndex,
         -- ** From strings to constructors and vice versa: all data types
         showConstr,
-        readConstr,
 
         -- * Convenience functions: take type constructors apart
         tyconUQname,
@@ -126,10 +126,8 @@ import GHC.Internal.Base (
 import GHC.Internal.Err (errorWithoutStackTrace)
 import GHC.Internal.List
 import GHC.Internal.Num
-import GHC.Internal.Read
 import GHC.Internal.Show
 import GHC.Internal.Tuple (Solo (..))
-import GHC.Internal.Text.Read( reads )
 import GHC.Internal.Types (
     Bool(..), Char, Coercible, Float, Double, Type, type (~), type (~~),
   )
@@ -688,32 +686,6 @@ showConstr :: Constr -> String
 showConstr = constring

--- | Lookup a constructor via a string
-readConstr :: DataType -> String -> Maybe Constr
-readConstr dt str =
-      case dataTypeRep dt of
-        AlgRep cons -> idx cons
-        IntRep      -> mkReadCon (\i -> (mkPrimCon dt str (IntConstr i)))
-        FloatRep    -> mkReadCon ffloat
-        CharRep     -> mkReadCon (\c -> (mkPrimCon dt str (CharConstr c)))
-        NoRep       -> Nothing
-  where
-
-    -- Read a value and build a constructor
-    mkReadCon :: Read t => (t -> Constr) -> Maybe Constr
-    mkReadCon f = case (reads str) of
-                    [(t,"")] -> Just (f t)
-                    _ -> Nothing
-
-    -- Traverse list of algebraic datatype constructors
-    idx :: [Constr] -> Maybe Constr
-    idx cons = case filter ((==) str . showConstr) cons of
-                [] -> Nothing
-                hd : _ -> Just hd
-
-    ffloat :: Double -> Constr
-    ffloat =  mkPrimCon dt str . FloatConstr . toRational
-
 ------------------------------------------------------------------------------
 --
 --      Convenience functions: algebraic data types


=====================================
testsuite/tests/interface-stability/base-exports.stdout
=====================================
@@ -12545,13 +12545,12 @@ instance [safe] GHC.Internal.Read.Read GHC.Stats.RTSStats -- Defined in ‘GHC.S
 instance GHC.Internal.Read.Read GHC.Internal.TypeNats.SomeNat -- Defined in ‘GHC.Internal.TypeNats’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeChar -- Defined in ‘GHC.Internal.TypeLits’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeSymbol -- Defined in ‘GHC.Internal.TypeLits’
-instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.BufferMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.IOMode.IOMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.Newline -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.NewlineMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Device.SeekMode -- Defined in ‘System.IO’
-instance forall a k (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
+instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance forall a. GHC.Internal.Float.RealFloat a => GHC.Internal.Real.Fractional (Data.Complex.Complex a) -- Defined in ‘Data.Complex’
 instance forall k (a :: k). Data.Fixed.HasResolution a => GHC.Internal.Real.Fractional (Data.Fixed.Fixed a) -- Defined in ‘Data.Fixed’
 instance forall k1 k2 (f :: k1 -> *) (g :: k2 -> k1) (a :: k2). GHC.Internal.Real.Fractional (f (g a)) => GHC.Internal.Real.Fractional (Data.Functor.Compose.Compose f g a) -- Defined in ‘Data.Functor.Compose’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-javascript-unknown-ghcjs
=====================================
@@ -12574,13 +12574,12 @@ instance [safe] GHC.Internal.Read.Read GHC.Stats.RTSStats -- Defined in ‘GHC.S
 instance GHC.Internal.Read.Read GHC.Internal.TypeNats.SomeNat -- Defined in ‘GHC.Internal.TypeNats’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeChar -- Defined in ‘GHC.Internal.TypeLits’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeSymbol -- Defined in ‘GHC.Internal.TypeLits’
-instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.BufferMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.IOMode.IOMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.Newline -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.NewlineMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Device.SeekMode -- Defined in ‘System.IO’
-instance forall a k (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
+instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance forall a. GHC.Internal.Float.RealFloat a => GHC.Internal.Real.Fractional (Data.Complex.Complex a) -- Defined in ‘Data.Complex’
 instance forall k (a :: k). Data.Fixed.HasResolution a => GHC.Internal.Real.Fractional (Data.Fixed.Fixed a) -- Defined in ‘Data.Fixed’
 instance forall k1 k2 (f :: k1 -> *) (g :: k2 -> k1) (a :: k2). GHC.Internal.Real.Fractional (f (g a)) => GHC.Internal.Real.Fractional (Data.Functor.Compose.Compose f g a) -- Defined in ‘Data.Functor.Compose’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-mingw32
=====================================
@@ -12817,13 +12817,12 @@ instance [safe] GHC.Internal.Read.Read GHC.Stats.RTSStats -- Defined in ‘GHC.S
 instance GHC.Internal.Read.Read GHC.Internal.TypeNats.SomeNat -- Defined in ‘GHC.Internal.TypeNats’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeChar -- Defined in ‘GHC.Internal.TypeLits’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeSymbol -- Defined in ‘GHC.Internal.TypeLits’
-instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.BufferMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.IOMode.IOMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.Newline -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.NewlineMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Device.SeekMode -- Defined in ‘System.IO’
-instance forall a k (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
+instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance forall a. GHC.Internal.Float.RealFloat a => GHC.Internal.Real.Fractional (Data.Complex.Complex a) -- Defined in ‘Data.Complex’
 instance forall k (a :: k). Data.Fixed.HasResolution a => GHC.Internal.Real.Fractional (Data.Fixed.Fixed a) -- Defined in ‘Data.Fixed’
 instance forall k1 k2 (f :: k1 -> *) (g :: k2 -> k1) (a :: k2). GHC.Internal.Real.Fractional (f (g a)) => GHC.Internal.Real.Fractional (Data.Functor.Compose.Compose f g a) -- Defined in ‘Data.Functor.Compose’


=====================================
testsuite/tests/interface-stability/base-exports.stdout-ws-32
=====================================
@@ -12545,13 +12545,12 @@ instance [safe] GHC.Internal.Read.Read GHC.Stats.RTSStats -- Defined in ‘GHC.S
 instance GHC.Internal.Read.Read GHC.Internal.TypeNats.SomeNat -- Defined in ‘GHC.Internal.TypeNats’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeChar -- Defined in ‘GHC.Internal.TypeLits’
 instance GHC.Internal.Read.Read GHC.Internal.TypeLits.SomeSymbol -- Defined in ‘GHC.Internal.TypeLits’
-instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.BufferMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.IOMode.IOMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.Newline -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Handle.Types.NewlineMode -- Defined in ‘System.IO’
 instance GHC.Internal.Read.Read GHC.Internal.IO.Device.SeekMode -- Defined in ‘System.IO’
-instance forall a k (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
+instance forall k a (b :: k). GHC.Internal.Real.Fractional a => GHC.Internal.Real.Fractional (GHC.Internal.Data.Functor.Const.Const a b) -- Defined in ‘GHC.Internal.Data.Functor.Const’
 instance forall a. GHC.Internal.Float.RealFloat a => GHC.Internal.Real.Fractional (Data.Complex.Complex a) -- Defined in ‘Data.Complex’
 instance forall k (a :: k). Data.Fixed.HasResolution a => GHC.Internal.Real.Fractional (Data.Fixed.Fixed a) -- Defined in ‘Data.Fixed’
 instance forall k1 k2 (f :: k1 -> *) (g :: k2 -> k1) (a :: k2). GHC.Internal.Real.Fractional (f (g a)) => GHC.Internal.Real.Fractional (Data.Functor.Compose.Compose f g a) -- Defined in ‘Data.Functor.Compose’



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d70ced0611c212293c28738f720f2576...

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View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/d70ced0611c212293c28738f720f2576...
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Wolfgang Jeltsch (＠jeltsch)

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