Work with a StateT transformator

It would be nice if we can also use a StateT monad transformer when walking through the AST and thus keep track of the section, and update the state based on content that we see when "walking" over the tree.

walkM in Text.Pandoc.Walk works for any monad. So yes, you can use it with a state monad or something else with StateT. Am I missing something in your question?

After rereading, I realized it was missing the most important part: the toJSONFilter which does not seem to allow effectively walk over this.

The implementation looks like

pandoc-types/src/Text/Pandoc/JSON.hs

Lines 120 to 124 in da9aeed

    
           instance (Walkable [a] Pandoc) => ToJSONFilter (a -> IO [a]) where 
        
             toJSONFilter f = BL.getContents >>= 
        
                (walkM (fmap concat . mapM f) :: Pandoc -> IO Pandoc) . 
        
                either error id . eitherDecode' >>= 
        
                BL.putStr . encode

so probably generalizing it to any monad transformer with IO as the "outer" one is possible. I will take a look into it.

Yes, maybe we could generalize these to any MonadIO instance.
An alternative approach that should work already would be to use the IO Monad and an IORef for state.

Closed by #105.

	instance (Walkable [a] Pandoc) => ToJSONFilter (a -> IO [a]) where
	toJSONFilter f = BL.getContents >>=
	(walkM (fmap concat . mapM f) :: Pandoc -> IO Pandoc) .
	either error id . eitherDecode' >>=
	BL.putStr . encode