haskell-src-meta-0.8.3: examples/Hs.hs

-- | Eat your face!

module Hs (hs, pat) where

import Language.Haskell.Meta       (parseExp, parsePat)
import Language.Haskell.Meta.Utils (pretty)
import Language.Haskell.TH.Lib
import Language.Haskell.TH.Quote
import Language.Haskell.TH.Syntax

import qualified Control.Monad.Fail as Fail

-- TODO: narrow type & move to shared module
quoteTypeNotImplemented :: Fail.MonadFail m => String -> m a
quoteTypeNotImplemented = fail . ("type quoter not implemented: " ++)

-- TODO: narrow type & move to shared module
quoteDecNotImplemented :: Fail.MonadFail m => String -> m a
quoteDecNotImplemented = fail . ("dec quoter not implemented: " ++ )

-- |
-- > ghci> [$hs|\x -> (x,x)|] 42
-- > (42,42)
-- > ghci> (\[$hs|a@(x,_)|] -> (a,x)) (42,88)
-- > ((42,88),42)
hs :: QuasiQuoter
hs = QuasiQuoter
      { quoteExp = either fail transformE . parseExp
      , quotePat = either fail transformP . parsePat
      , quoteType = quoteTypeNotImplemented
      , quoteDec = quoteDecNotImplemented
      }

transformE :: Exp -> ExpQ
transformE = return

transformP :: Pat -> PatQ
transformP = return

pat :: QuasiQuoter
pat = QuasiQuoter
        { quoteExp = quoteExp hs
        , quotePat = \s -> case parseExp s of
                Left err -> fail err
                Right e  -> either fail return (parsePat . pretty $ e)
      , quoteType = quoteTypeNotImplemented
      , quoteDec = quoteDecNotImplemented
        }