4 files changed, 63 insertions, 10 deletions
diff --git a/compiler/Language/Haskell/Syntax.hs b/compiler/Language/Haskell/Syntax.hs
index d5129cbb13..82e9f5558d 100644
--- a/compiler/Language/Haskell/Syntax.hs
+++ b/compiler/Language/Haskell/Syntax.hs
@@ -22,6 +22,7 @@ module Language.Haskell.Syntax (
         module Language.Haskell.Syntax.Expr,
         module Language.Haskell.Syntax.ImpExp,
         module Language.Haskell.Syntax.Lit,
+        module Language.Haskell.Syntax.Module.Name,
         module Language.Haskell.Syntax.Pat,
         module Language.Haskell.Syntax.Type,
         module Language.Haskell.Syntax.Extension,
@@ -32,6 +33,7 @@ import Language.Haskell.Syntax.Decls
 import Language.Haskell.Syntax.Binds
 import Language.Haskell.Syntax.Expr
 import Language.Haskell.Syntax.ImpExp
+import Language.Haskell.Syntax.Module.Name
 import Language.Haskell.Syntax.Lit
 import Language.Haskell.Syntax.Extension
 import Language.Haskell.Syntax.Pat
diff --git a/compiler/Language/Haskell/Syntax/ImpExp.hs b/compiler/Language/Haskell/Syntax/ImpExp.hs
index 7e529701c4..b31c417936 100644
--- a/compiler/Language/Haskell/Syntax/ImpExp.hs
+++ b/compiler/Language/Haskell/Syntax/ImpExp.hs
@@ -3,6 +3,7 @@
 module Language.Haskell.Syntax.ImpExp where
 
 import Language.Haskell.Syntax.Extension
+import Language.Haskell.Syntax.Module.Name
 
 import Data.Eq (Eq)
 import Data.Ord (Ord)
@@ -14,7 +15,6 @@ import Data.String (String)
 import Data.Int (Int)
 
 import GHC.Hs.Doc -- ROMES:TODO Discuss in #21592 whether this is parsed AST or base AST
-import GHC.Data.FastString
 
 {-
 ************************************************************************
@@ -26,9 +26,6 @@ Import and export declaration lists
 One per import declaration in a module.
 -}
 
--- | A ModuleName is essentially a simple string, e.g. @Data.List@.
-newtype ModuleName = ModuleName FastString deriving Show
-
 -- | Located Import Declaration
 type LImportDecl pass = XRec pass (ImportDecl pass)
         -- ^ When in a list this may have
diff --git a/compiler/Language/Haskell/Syntax/ImpExp.hs-boot b/compiler/Language/Haskell/Syntax/ImpExp.hs-boot
index 9cc78600b8..68bd7fdc53 100644
--- a/compiler/Language/Haskell/Syntax/ImpExp.hs-boot
+++ b/compiler/Language/Haskell/Syntax/ImpExp.hs-boot
@@ -1,7 +1,5 @@
 module Language.Haskell.Syntax.ImpExp where
 
-import GHC.Data.FastString
-
 import Data.Eq
 import Data.Ord
 import Text.Show
@@ -16,7 +14,3 @@ instance Eq IsBootInterface
 instance Ord IsBootInterface
 instance Show IsBootInterface
 instance Data IsBootInterface
-
-newtype ModuleName = ModuleName FastString
-
-instance Show ModuleName
diff --git a/compiler/Language/Haskell/Syntax/Module/Name.hs b/compiler/Language/Haskell/Syntax/Module/Name.hs
new file mode 100644
index 0000000000..65e64d8700
--- /dev/null
+++ b/compiler/Language/Haskell/Syntax/Module/Name.hs
@@ -0,0 +1,60 @@
+module Language.Haskell.Syntax.Module.Name where
+
+import Prelude
+
+import Data.Data
+import Data.Char (isAlphaNum)
+import Control.DeepSeq
+import qualified Text.ParserCombinators.ReadP as Parse
+import System.FilePath
+
+import GHC.Utils.Misc (abstractConstr)
+import GHC.Data.FastString
+
+-- | A ModuleName is essentially a simple string, e.g. @Data.List@.
+newtype ModuleName = ModuleName FastString deriving (Show, Eq)
+
+instance Ord ModuleName where
+  nm1 `compare` nm2 = stableModuleNameCmp nm1 nm2
+
+instance Data ModuleName where
+  -- don't traverse?
+  toConstr _   = abstractConstr "ModuleName"
+  gunfold _ _  = error "gunfold"
+  dataTypeOf _ = mkNoRepType "ModuleName"
+
+instance NFData ModuleName where
+  rnf x = x `seq` ()
+
+stableModuleNameCmp :: ModuleName -> ModuleName -> Ordering
+-- ^ Compares module names lexically, rather than by their 'Unique's
+stableModuleNameCmp n1 n2 = moduleNameFS n1 `lexicalCompareFS` moduleNameFS n2
+
+moduleNameFS :: ModuleName -> FastString
+moduleNameFS (ModuleName mod) = mod
+
+moduleNameString :: ModuleName -> String
+moduleNameString (ModuleName mod) = unpackFS mod
+
+mkModuleName :: String -> ModuleName
+mkModuleName s = ModuleName (mkFastString s)
+
+mkModuleNameFS :: FastString -> ModuleName
+mkModuleNameFS s = ModuleName s
+
+-- |Returns the string version of the module name, with dots replaced by slashes.
+--
+moduleNameSlashes :: ModuleName -> String
+moduleNameSlashes = dots_to_slashes . moduleNameString
+  where dots_to_slashes = map (\c -> if c == '.' then pathSeparator else c)
+
+-- |Returns the string version of the module name, with dots replaced by colons.
+--
+moduleNameColons :: ModuleName -> String
+moduleNameColons = dots_to_colons . moduleNameString
+  where dots_to_colons = map (\c -> if c == '.' then ':' else c)
+
+parseModuleName :: Parse.ReadP ModuleName
+parseModuleName = fmap mkModuleName
+                $ Parse.munch1 (\c -> isAlphaNum c || c `elem` "_.")
+