Re: [Haskell-cafe] prettyprint with IO

On Thu, 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

On this note, there are various Wadler-Leijin pretty printers variants on hackage, some lifted into a monad so you can do effects, IO, or whatever. E.g. wl-pprint-extras. In my experience though WL gives worse results than H-PJ despite having some more powerful operators.