Hello all,

SYB uses DataRep to represent datatypes:

    -- | Public representation of datatypes
    data DataRep = AlgRep [Constr]
                 | IntRep
                 | FloatRep
                 | StringRep
                 | NoRep

I believe that StringRep should be CharRep. Note that IntRep is used for the primitive Int and Integer datatypes, FloatRep for Float and Double, and StringRep (apparently) for Char. String, however, is represented as AlgRep [[],(:)]:

    *Main> dataTypeOf 'p'
    DataType {tycon = "Prelude.Char", datarep = StringRep}
    *Main> dataTypeOf "p"
    DataType {tycon = "Prelude.[]", datarep = AlgRep [[],(:)]}

This makes sense, since String is not a primitive datatype. But it causes the apparently wrong behavior:

    *Main> fromConstr (mkStringConstr (dataTypeOf "a") "ab") :: String
    "*** Exception: mkStringConstr
    *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: String
    "*** Exception: constrIndex

The correct way of using mkStringConstr is to construct a Char. This, however, only works for strings with a single character:

    *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "b") :: Char
    'b'
    *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: Char
    *** Exception: gunfold
    *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "")   :: Char
    *** Exception: gunfold

I find this behavior counterintuitive. Therefore I propose to rename StringRep to CharRep and mkStringConstr to mkCharConstr. For backwards compatibility, this entails:

    * Deprecating mkStringConstr and StringConstr
    * Deprecating mkStringRep and StringRep
    * Introducing mkCharConstr and CharConstr
    * Introducing mkCharRep and CharRep

Additionally, due to deprecation warnings, the following have to change as well:

    * libraries/template-haskell/Language/Haskell/TH/Quote.hs
    * compiler/utils/Serialized.hs

A patch is attached in #2875 (http://hackage.haskell.org/trac/ghc/ticket/2875). I propose a discussion period of 4 weeks, therefore until the 8th of January.

Thanks,
Pedro