I'm looking for a reliable way to turn values into Template Haskell expressions. I thought dataToExpQ from Language.Haskell.TH.Quote was the ticket, but it appears to produce constructors different from those produced by [| ... |], including [], (:), (), and (,). Here's an example run for (). I'm using template-haskell-2.5.0.0:
GHCi, version 7.0.4: http://www.haskell.org/ghc/ :? for help
Prelude> import Data.Data
Prelude Data.Data> import Language.Haskell.TH
Prelude Data.Data Language.Haskell.TH> :set -XTemplateHaskell
Prelude Data.Data Language.Haskell.TH> import Language.Haskell.TH.Quote
Prelude Data.Data Language.Haskell.TH Language.Haskell.TH.Quote> u1 <- runQ (dataToExpQ (const Nothing) ())
Prelude Data.Data Language.Haskell.TH Language.Haskell.TH.Quote> u2 <- runQ [| () |]
Prelude Data.Data Language.Haskell.TH Language.Haskell.TH.Quote> u1
ConE ()
Prelude Data.Data Language.Haskell.TH Language.Haskell.TH.Quote> u2
ConE GHC.Unit.()
Prelude Data.Data Language.Haskell.TH Language.Haskell.TH.Quote> u1 == u2
False
Any suggestions?
-- Conal