    -- |Computations in the vectorisation monad concerned with naming and fresh variable generation.

    module Vectorise.Monad.Naming
      ( mkLocalisedName
      , mkDerivedName
      , mkVectId
      , cloneVar
      , newExportedVar
      , newLocalVar
      , newLocalVars
      , newDummyVar
      , newTyVar
      )
    where

    import Vectorise.Monad.Base

    import DsMonad
    import TcType
    import Type
    import Var
    import Module
    import Name
    import SrcLoc
    import MkId
    import Id
    import IdInfo( IdDetails(VanillaId) )
    import FastString

    import Control.Monad

    -- Naming ---------------------------------------------------------------------

    -- |Create a localised variant of a name, using the provided function to transform its `OccName`.
    --
    -- If the name external, encode the orignal name's module into the new 'OccName'.  The result is
    -- always an internal system name.
    --
    mkLocalisedName :: (Maybe String -> OccName -> OccName) -> Name -> VM Name
    mkLocalisedName mk_occ name
      = do { mod <- liftDs getModule
           ; u   <- liftDs newUnique
           ; let occ_name = mkLocalisedOccName mod mk_occ name

                 new_name | isExternalName name = mkExternalName u mod occ_name (nameSrcSpan name)
                          | otherwise           = mkSystemName   u     occ_name

           ; return new_name }

    mkDerivedName :: (OccName -> OccName) -> Name -> VM Name
    -- Similar to mkLocalisedName, but assumes the
    -- incoming name is from this module.
    -- Works on External names only
    mkDerivedName mk_occ name
      = do { u   <- liftDs newUnique
           ; return (mkExternalName u (nameModule name)
                                      (mk_occ (nameOccName name))
                                      (nameSrcSpan name)) }

    -- |Produce the vectorised variant of an `Id` with the given vectorised type, while taking care that
    -- vectorised dfun ids must be dfuns again.
    --
    -- Force the new name to be a system name and, if the original was an external name, disambiguate
    -- the new name with the module name of the original.
    --
    mkVectId :: Id -> Type -> VM Id
    mkVectId id ty
      = do { name <- mkLocalisedName mkVectOcc (getName id)
           ; let id' | isDFunId id     = MkId.mkDictFunId name tvs theta cls tys
                     | isExportedId id = Id.mkExportedLocalId VanillaId name ty
                     | otherwise       = Id.mkLocalId         name ty
           ; return id'
           }
      where
        -- Decompose a dictionary function signature: \forall tvs. theta -> cls tys
        -- NB: We do *not* use closures '(:->)' for vectorised predicate abstraction as dictionary
        --     functions are always fully applied.
        (tvs, theta, pty) = tcSplitSigmaTy  ty
        (cls, tys)        = tcSplitDFunHead pty

    -- |Make a fresh instance of this var, with a new unique.
    --
    cloneVar :: Var -> VM Var
    cloneVar var = liftM (setIdUnique var) (liftDs newUnique)

    -- |Make a fresh exported variable with the given type.
    --
    newExportedVar :: OccName -> Type -> VM Var
    newExportedVar occ_name ty
     = do mod <- liftDs getModule
          u   <- liftDs newUnique

          let name = mkExternalName u mod occ_name noSrcSpan

          return $ Id.mkExportedLocalId VanillaId name ty

    -- |Make a fresh local variable with the given type.
    -- The variable's name is formed using the given string as the prefix.
    --
    newLocalVar :: FastString -> Type -> VM Var
    newLocalVar fs ty
     = do u <- liftDs newUnique
          return $ mkSysLocal fs u ty

    -- |Make several fresh local variables with the given types.
    -- The variable's names are formed using the given string as the prefix.
    --
    newLocalVars :: FastString -> [Type] -> VM [Var]
    newLocalVars fs = mapM (newLocalVar fs)

    -- |Make a new local dummy variable.
    --
    newDummyVar :: Type -> VM Var
    newDummyVar = newLocalVar (fsLit "vv")

    -- |Make a fresh type variable with the given kind.
    -- The variable's name is formed using the given string as the prefix.
    --
    newTyVar :: FastString -> Kind -> VM Var
    newTyVar fs k
     = do u <- liftDs newUnique
          return $ mkTyVar (mkSysTvName u fs) k