Builtins: add doc on Nix import clause

Author: Anton-Latukha

src/Nix/Builtins.hs

@@ -1202,6 +1202,16 @@ throwNix mnv =
 
     throwError . ErrorCall . toString $ stringIgnoreContext ns
 
+-- | Implementation of Nix @import@ clause.
+--
+-- Because Nix @import@s work strictly
+-- (import gets fully evaluated befor bringing it into the scope it was called from)
+-- - that property raises a requirement for execution phase of the interpreter go into evaluation phase
+-- & then also go into parsing phase on the imports.
+-- So it is not possible (more precise - not practical) to do a full parse Nix code phase fully & then go into evaluation phase.
+-- As it is not possible to "import them lazily", as import is strict & it is not possible to establish
+-- what imports whould be needed up until where it would be determined & they import strictly
+--
 importNix
   :: forall e t f m . MonadNix e t f m => NValue t f m -> m (NValue t f m)
 importNix = scopedImportNix $ nvSet mempty mempty

src/Nix/Convert.hs

@@ -211,7 +211,7 @@ instance Convertible e t f m
   => FromValue ByteString m (NValue' t f m (NValue t f m)) where
 
   fromValueMay =
-    pure.
+    pure .
       \case
         NVStr' ns -> encodeUtf8 <$> getStringNoContext  ns
         _         -> mempty