Define readOrFail as a general function

hindent.cabal

@@ -46,6 +46,7 @@ library
                      HIndent.Pretty.Imports.Sort
                      HIndent.Pretty.ModuleDeclaration
                      HIndent.Pretty.Pragma
+                     HIndent.Read
                      HIndent.RelocateComments
                      HIndent.SrcSpan
                      HIndent.Types

src/HIndent/CabalFile.hs

@@ -25,10 +25,10 @@ import           GHC.Driver.Session                            (impliedXFlags,
 import qualified GHC.Driver.Session                            as GLP
 import qualified GHC.LanguageExtensions.Type                   as GLP
 import qualified HIndent.ExtensionConversion                   as EC
+import           HIndent.Read
 import           Language.Haskell.Extension
 import           System.Directory
 import           System.FilePath
-import           Text.Read
 
 data Stanza =
   MkStanza
@@ -166,9 +166,6 @@ getCabalExtensionsForSourcePath srcpath = do
 implicitExtensions :: GLP.Language -> [Extension]
 implicitExtensions =
   fmap (EnableExtension . readOrFail . show) . languageExtensions . Just
-  where
-    readOrFail x =
-      fromMaybe (error $ "Unsupported extension: " ++ show x) $ readMaybe x
 
 extensionImplies :: Extension -> [Extension]
 extensionImplies (EnableExtension e) =

src/HIndent/ExtensionConversion.hs

@@ -6,26 +6,19 @@ module HIndent.ExtensionConversion
   , convertExtension
   ) where
 
-import           Data.Maybe
 import qualified GHC.LanguageExtensions     as GLP
+import           HIndent.Read
 import qualified Language.Haskell.Extension as Cabal
-import           Text.Read
 
 gleExtensionToCabalExtension :: GLP.Extension -> Cabal.Extension
 gleExtensionToCabalExtension = readOrFail . show
-  where
-    readOrFail x =
-      fromMaybe (error $ "Unsupported extension: " ++ show x) $ readMaybe x
 
 uniqueExtensions :: [Cabal.Extension] -> [GLP.Extension]
 uniqueExtensions [] = []
 uniqueExtensions ((Cabal.EnableExtension e):xs) =
   convertExtension e : uniqueExtensions xs
 uniqueExtensions ((Cabal.DisableExtension e):xs) =
   uniqueExtensions $ filter (/= readOrFail (show e)) xs
-  where
-    readOrFail x =
-      fromMaybe (error $ "Unsupported extension: " ++ show x) $ readMaybe x
 uniqueExtensions ((Cabal.UnknownExtension s):_) =
   error $ "Unknown extension: " ++ s
 

src/HIndent/Read.hs

@@ -0,0 +1,14 @@
+module HIndent.Read
+  ( readOrFail
+  ) where
+
+import           Data.Maybe
+import           GHC.Stack
+import           Text.Read
+
+-- | `read` but dumps a stack trace if reading a value fails.
+readOrFail ::
+     HasCallStack
+  => Read a =>
+       String -> a
+readOrFail x = fromMaybe (error $ "`read` failed: " ++ x) $ readMaybe x