[Haskell-beginners] Defining of subset of constructors as valid values

[Lev Broido]

Hi all
I have the following code :

data CmdTiming  = RAS Time | CAS Time | PCH Time | ACT Time deriving
(Ord,Show,Eq)

data Command  =
  RD_CMD {bank :: Int, col :: Int }  |
  WR_CMD {bank :: Int, col :: Int}  |
  ACT_CMD {bank :: Int, row :: Int} |
  PCH_CMD {bank :: Int} deriving Show

I'd like to have something like :
RD_CMD {bank :: Int, col :: Int,timing :: RAS Time }
to limit possible values to RAS Time .

The reason I use constructors is differentiate whether current value is
applicable to some function , getting CmdTiming as parameter or not .

I am not sure this is valid definition since RAS Time is not type .

Regards,
Lev
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