patch applied (ghc): Deriving for indexed data types

Mon Dec 18 13:12:05 PST 2006  Manuel M T Chakravarty <[email protected]>
  * Deriving for indexed data types
  - This patch implements deriving clauses for data instance declarations
    (toplevel and associated)
  - Doesn't support standalone deriving.  This could be easily supported,
    but requires an extension of the syntax of standalone deriving clauses.
    Bj[_\c3_][_\b6_]rn, fancy adding this?
  - We cannot derive Typeable.  This seems a problem of notation, more than 
    anything else.  Why?  For a binary vanilla data type "T a b", we would 
    generate an instance Typeable2 T; ie, the instance is for the constructor
    alone.  In the case of a family instance, such as (S [a] (Maybe b)), we
    simply have no means to denote the associated constuctor.  It appears to
    require type level lambda - something like (/\a b. S [a] (Maybe b).
  - Derivings are for *individual* family *instances*, not for entire families.
    Currently, I know of no simple translation of class instances for entire 
    families to System F_C.  This actually seems to be similar to implementing
    open data types [_\c3_][_\a0_] la L[_\c3_][_\b6_]h & Hinze.
  - This patch only covers data types, not newtypes.

    M ./compiler/typecheck/TcDeriv.lhs -59 +111
    M ./compiler/typecheck/TcEnv.lhs -1 +19
    M ./compiler/types/FamInstEnv.lhs -2 +46
    M ./compiler/types/Type.lhs +8