Value: {iterNValue: unflip 2nd arg, add iterNValueByDiscardWith, notes}

Author: Anton-Latukha

src/Nix/Normal.hs

@@ -19,7 +19,6 @@ import           Data.Set                  ( member
                                            )
 import           Nix.Cited
 import           Nix.Frames
-import           Nix.String
 import           Nix.Thunk
 import           Nix.Value
 
@@ -156,7 +155,7 @@ stubCycles
   -> NValue t f m
 stubCycles =
   iterNValue
-    (\t _ ->
+    (\_ t ->
       Free $
         NValue' $
           foldr

src/Nix/Pretty.hs

@@ -307,7 +307,7 @@ exprFNixDoc = \case
 
 
 valueToExpr :: forall t f m . MonadDataContext f m => NValue t f m -> NExpr
-valueToExpr = iterNValue (\_ _ -> thk) (Fix . phi)
+valueToExpr = iterNValueByDiscardWith thk (Fix . phi)
  where
   thk = Fix . NSym $ "<expr>"
 
@@ -372,7 +372,7 @@ prettyNThunk t =
 
 -- | This function is used only by the testing code.
 printNix :: forall t f m . MonadDataContext f m => NValue t f m -> String
-printNix = iterNValue (\_ _ -> thk) phi
+printNix = iterNValueByDiscardWith thk phi
  where
   thk = toString thunkStubText
 

src/Nix/Value.hs

@@ -513,18 +513,26 @@ type NValue t f m = Free (NValue' t f m) t
 
 -- ** Free
 
--- | @iter@
+-- | HOF of @iter@ from @Free@
 iterNValue
   :: forall t f m r
    . MonadDataContext f m
-  => (t -> (NValue t f m -> r) -> r)
+  => ((Free (NValue' t f m) t -> r) -> t -> r)
   -> (NValue' t f m r -> r)
-  -> NValue t f m
+  -> Free (NValue' t f m) t
+  -> r
+iterNValue k f = iter f . fmap (k (iterNValue k f))
+
+iterNValueByDiscardWith
+  :: MonadDataContext f m
+  => r
+  -> (NValue' t f m r -> r)
+  -> Free (NValue' t f m) t
   -> r
-iterNValue k f = iter f . fmap (\t -> k t $ iterNValue k f)
+iterNValueByDiscardWith dflt = iterNValue (\ _ _ -> dflt)
 
 
--- | @iter@ for monadic values
+-- | HOF of @iterM@ from @Free@
 iterNValueM
   :: (MonadDataContext f m, Monad n)
   => (forall x . n x -> m x)

src/Nix/XML.hs

@@ -17,7 +17,7 @@ import           Text.XML.Light                 ( Element(Element)
                                                 )
 
 toXML :: forall t f m . MonadDataContext f m => NValue t f m -> NixString
-toXML = runWithStringContext . fmap pp . iterNValue (\_ _ -> cyc) phi
+toXML = runWithStringContext . fmap pp . iterNValueByDiscardWith cyc phi
  where
   cyc = pure $ mkEVal "string" "<expr>"