Move the caching support code into its own Nix.Cache module

hnix.cabal

@@ -2,7 +2,7 @@
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: 13b58b4fb9f715dd28ba6e47cb5feeb0da553ac1b16b356677c580f8b71f70e6
+-- hash: 00ae617f664cd9dc67f4a6551a0e3c0eee19899f21b44c6dda24e17618a8fb5d
 
 name:           hnix
 version:        0.5.0
@@ -30,6 +30,7 @@ library
       Nix
       Nix.Atoms
       Nix.Builtins
+      Nix.Cache
       Nix.Context
       Nix.Effects
       Nix.Eval

main/Main.hs

@@ -1,19 +1,13 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
 -- {-# LANGUAGE QuasiQuotes #-}
 
-#ifdef __linux__
-#define USE_COMPACT 1
-#endif
-
 module Main where
 
 import           Control.DeepSeq
 import qualified Control.Exception as Exc
 import           Control.Monad
 import           Control.Monad.ST
-import qualified Data.ByteString.Lazy as BS
 import           Data.Text (Text, pack)
 import qualified Data.Text.IO as Text
 import qualified Nix
@@ -28,13 +22,6 @@ import           System.IO
 import           System.FilePath
 import           Text.PrettyPrint.ANSI.Leijen hiding ((<$>))
 
-#ifdef USE_COMPACT
-import qualified Data.Compact as C
-import qualified Data.Compact.Serialize as C
-#else
-import qualified Codec.Serialise as S
-#endif
-
 data Options = Options
     { verbose      :: Bool
     , debug        :: Bool
@@ -109,21 +96,8 @@ main = do
     opts <- execParser optsDef
     case readFrom opts of
         Just path -> do
-#ifdef USE_COMPACT
-            eres <- C.unsafeReadCompact path
-            case eres of
-                Left err -> error $ "Error reading cache file: " ++ err
-                Right expr -> do
-                    let file = addExtension (dropExtension path) "nix"
-                    process opts (Just file) (C.getCompact expr)
-#else
-            eres <- S.deserialiseOrFail <$> BS.readFile path
-            case eres of
-                Left err -> error $ "Error reading cache file: " ++ show err
-                Right expr -> do
-                    let file = addExtension (dropExtension path) "nix"
-                    process opts (Just file) expr
-#endif
+            let file = addExtension (dropExtension path) "nix"
+            process opts (Just file) =<< readCache path
         Nothing -> case expression opts of
             Just s -> handleResult opts Nothing (parseNixTextLoc s)
             Nothing  -> case fromFile opts of
@@ -177,21 +151,9 @@ main = do
                  putStrLn . printNix =<< Nix.evalLoc mpath expr
            | debug opts ->
                  print $ stripAnnotation expr
-           | cache opts ->
-#ifdef USE_COMPACT
-                 do cx <- C.compact expr
-                    case mpath of
-                        Nothing -> return ()
-                        Just path -> do
-                            let file = addExtension (dropExtension path) "nixc"
-                            C.writeCompact file cx
-#else
-                 case mpath of
-                     Nothing -> return ()
-                     Just path -> do
-                         let file = addExtension (dropExtension path) "nixc"
-                         BS.writeFile file (S.serialise expr)
-#endif
+           | cache opts, Just path <- mpath -> do
+                let file = addExtension (dropExtension path) "nixc"
+                writeCache file expr
            | parseOnly opts ->
                  void $ Exc.evaluate $ force expr
            | otherwise ->

src/Nix/Cache.hs

@@ -0,0 +1,39 @@
+{-# LANGUAGE CPP #-}
+
+module Nix.Cache where
+
+import qualified Data.ByteString.Lazy as BS
+import           Nix.Expr.Types.Annotated
+
+#ifdef __linux__
+#define USE_COMPACT 1
+#endif
+
+#ifdef USE_COMPACT
+import qualified Data.Compact as C
+import qualified Data.Compact.Serialize as C
+#else
+import qualified Codec.Serialise as S
+#endif
+
+readCache :: FilePath -> IO NExprLoc
+readCache path = do
+#ifdef USE_COMPACT
+    eres <- C.unsafeReadCompact path
+    case eres of
+        Left err -> error $ "Error reading cache file: " ++ err
+        Right expr -> return $ C.getCompact expr
+#else
+    eres <- S.deserialiseOrFail <$> BS.readFile path
+    case eres of
+        Left err -> error $ "Error reading cache file: " ++ show err
+        Right expr -> return expr
+#endif
+
+writeCache :: FilePath -> NExprLoc -> IO ()
+writeCache path expr =
+#ifdef USE_COMPACT
+    C.writeCompact path =<< C.compact expr
+#else
+    BS.writeFile path (S.serialise expr)
+#endif

src/Nix/Expr/Types.hs

@@ -111,6 +111,8 @@ instance Lift (Fix NExprF) where
 -- | The monomorphic expression type is a fixed point of the polymorphic one.
 type NExpr = Fix NExprF
 
+instance Serialise NExpr
+
 -- | A single line of the bindings section of a let expression or of a set.
 data Binding r
   = NamedVar !(NAttrPath r) !r