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I am working on a project using Heist, and since it recently upgrade to 0.13 version, I tried it out and find the original HeistConfig changed a lot. 

data HeistConfig m = HeistConfig
    { hcInterpretedSplices :: Splices (I.Splice m)
        -- ^ Interpreted splices are the splices that Heist has always had.  They
        -- return a list of nodes and are processed at runtime.
    , hcLoadTimeSplices    :: Splices (I.Splice IO)
        -- ^ Load time splices are like interpreted splices because they return a
        -- list of nodes.  But they are like compiled splices because they are
        -- processed once at load time.  All of Heist's built-in splices should be
        -- used as load time splices.
    , hcCompiledSplices    :: Splices (C.Splice m)
        -- ^ Compiled splices return a DList of Chunks and are processed at load
        -- time to generate a runtime monad action that will be used to render the
        -- template.
    , hcAttributeSplices   :: Splices (AttrSplice m)
        -- ^ Attribute splices are bound to attribute names and return a list of
        -- attributes.
    , hcTemplateLocations  :: [TemplateLocation]
        -- ^ A list of all the locations that Heist should get its templates
    }

So now I could no longer use [] as default Splices, since there are defaultInterpretedSplices and defaultLoadTimeSplices, I find the defaultAttrSplices just missed, so how shoud I define it?

bennofs
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Lynton
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1 Answers1

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I think there are no built-in AttrSplices. You should be able to bind no splices using one of mempty, return () or noSplices from Heist.SpliceAPI.

Splices s is a type alias for SplicesM s (), which is just a State wrapped in newtype. Slices s is also instance of Monoid type class so you can use mempty here.

newtype SplicesM s a = SplicesM { unSplices :: State (Map Text s) a }
  deriving (Monad, MonadState (Map Text s))

type Splices s = SplicesM s ()

instance Monoid (Splices s) where
  mempty = noSplices
  mappend = unionWithS (\_ b -> b)
sopvop
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  • sopvop is exactly right here. If you don't have any attribute splices, then use mempty. – mightybyte Sep 15 '13 at 20:34
  • `noSplices` works, but `mempty` is more general. Before Heist 0.13 we used lists to represent splices. If we had used `[]` to represent no splices, then 0.13 would have broken our code. But if we used `mempty`, it would have worked in both places. It is also worth remembering that any time you see that something has a Monoid instance, `mempty` is available to you for this purpose. – mightybyte Sep 16 '13 at 16:46