Antoine, Thanks for the suggestions. No sooner did I send my message than I came to the same conclusion of creating a monadic version of the combinators to simplify the migration. It actually worked out fairly well -- most of the code ported over to the monadic version unaltered. The only exception is with literal lists used by combinators such as 'sep', e.g. sep [...]. This has to become sep $ sequence [...] in order to convert the argument into the expected monad. I put my code up on github https://github.com/warrenharris/pretty/blob/master/src/Text/PrettyPrint/Read.... If you can take a look, I'd appreciate your suggestions. Warren On Apr 12, 2012, at 6:22 PM, Antoine Latter wrote:

Hi Warren,

On Thu, Apr 12, 2012 at 6:31 PM, Warren Harris wrote:

...

I wrote a parsec parser that does symbols lookups during the parsing process (ParsecT String Store IO a). Now I'd like to write a pretty printer that does the reverse. Unfortunately there doesn't appear to be a transformer version of Text.PrettyPrint.HughesPJ. Can anyone suggest a way to do this? Thanks,

It seems like the opposite would be a function of type 'a -> Store -> IO Doc'.

Maybe a function of type 'a -> ReaderT Store IO Doc' could be easier to work with.

If you go this route you could write a lifted versions of (<>), (<+>), hcat etc.

An example:

(<>) :: Applicative m => m Doc -> m Doc -> m Doc

I haven't tried any of this, so I'm not sure if you would get any big win over just using the first suggestion (a function of type 'a -> Store -> IO Doc') and using the stock combinators and threading the store around by hand.

But do let me know if something works out.

Antoine