On Thu, Jul 23, 2009 at 11:21 PM, Ashley Yakeley
David Menendez wrote:
instance Data Double where toConstr = mkFloatConstr floatType -- that should probably be "doubleType" gunfold _ z c = case constrRep c of (FloatConstr x) -> z x _ -> error "gunfold" dataTypeOf _ = doubleType
I could do something like this for Fixed, but deriving Fixed automatically does essentially the same thing.
It depends on how abstract you want Fixed to be. If you use the
derived Data instances, then gshow and gread (from Data.Generics.Text)
expose the implementation.
*Fixed Data.Generics.Text> gshow (4::Micro)
"(MkFixed (4000000))"
*Fixed Data.Generics.Text> gread "(MkFixed (4))" :: [(Micro,String)]
[(0.000004,"")]
*Fixed Data.Generics.Text> gread "(MkFixed (4))" :: [(Pico,String)]
[(0.000000000004,"")]
In contrast, the StringRep version I posted elsewhere works fine with
gshow/gread while still hiding the implementation.
*Main Data.Generics.Text> gshow (4::Micro)
"(4.000000)"
*Main Data.Generics.Text> gread "(4)" :: [(Micro,String)]
[(4.000000,"")]
*Main Data.Generics.Text> gread "(4)" :: [(Pico,String)]
[(4.000000000000,"")]
--
Dave Menendez