path: root/compiler/iface/BuildTyCl.lhs

%
% (c) The University of Glasgow 2006
% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%

\begin{code}
module BuildTyCl (
	buildSynTyCon, 
        buildAlgTyCon, 
        buildDataCon,
	TcMethInfo, buildClass,
	mkAbstractTyConRhs, 
	mkNewTyConRhs, mkDataTyConRhs, 
        newImplicitBinder
    ) where

#include "HsVersions.h"

import IfaceEnv

import DataCon
import Var
import VarSet
import BasicTypes
import Name
import MkId
import Class
import TyCon
import Type
import Coercion

import TcRnMonad
import Data.List	( partition )
import Outputable
\end{code}
	

\begin{code}
------------------------------------------------------
buildSynTyCon :: Name -> [TyVar] 
              -> SynTyConRhs
	      -> Kind			-- ^ Kind of the RHS
	      -> TyConParent
	      -> Maybe (TyCon, [Type])    -- ^ family instance if applicable
              -> TcRnIf m n TyCon
buildSynTyCon tc_name tvs rhs rhs_kind parent mb_family 
  | Just fam_inst_info <- mb_family
  = ASSERT( isNoParent parent )
    fixM $ \ tycon_rec -> do 
    { fam_parent <- mkFamInstParentInfo tc_name tvs fam_inst_info tycon_rec 
    ; return (mkSynTyCon tc_name kind tvs rhs fam_parent) }

  | otherwise
  = return (mkSynTyCon tc_name kind tvs rhs parent)
  where
    kind = mkArrowKinds (map tyVarKind tvs) rhs_kind

------------------------------------------------------
buildAlgTyCon :: Name -> [TyVar] 
	      -> ThetaType		-- ^ Stupid theta
	      -> AlgTyConRhs
	      -> RecFlag
	      -> Bool			-- ^ True <=> was declared in GADT syntax
              -> TyConParent
	      -> Maybe (TyCon, [Type])  -- ^ family instance if applicable
	      -> TcRnIf m n TyCon

buildAlgTyCon tc_name tvs stupid_theta rhs is_rec gadt_syn
	      parent mb_family
  | Just fam_inst_info <- mb_family
  = -- We need to tie a knot as the coercion of a data instance depends
     -- on the instance representation tycon and vice versa.
    ASSERT( isNoParent parent )
    fixM $ \ tycon_rec -> do 
    { fam_parent <- mkFamInstParentInfo tc_name tvs fam_inst_info tycon_rec
    ; return (mkAlgTyCon tc_name kind tvs stupid_theta rhs
		         fam_parent is_rec gadt_syn) }

  | otherwise
  = return (mkAlgTyCon tc_name kind tvs stupid_theta rhs
	               parent is_rec gadt_syn)
  where
    kind = mkArrowKinds (map tyVarKind tvs) liftedTypeKind

-- | If a family tycon with instance types is given, the current tycon is an
-- instance of that family and we need to
--
-- (1) create a coercion that identifies the family instance type and the
--     representation type from Step (1); ie, it is of the form 
--	   `Co tvs :: F ts ~ R tvs', where `Co' is the name of the coercion,
--	   `F' the family tycon and `R' the (derived) representation tycon,
--	   and
-- (2) produce a `TyConParent' value containing the parent and coercion
--     information.
--
mkFamInstParentInfo :: Name -> [TyVar] 
             	    -> (TyCon, [Type]) 
             	    -> TyCon 
             	    -> TcRnIf m n TyConParent
mkFamInstParentInfo tc_name tvs (family, instTys) rep_tycon
  = do { -- Create the coercion
       ; co_tycon_name <- newImplicitBinder tc_name mkInstTyCoOcc
       ; let co_tycon = mkFamInstCo co_tycon_name tvs
                                    family instTys rep_tycon
       ; return $ FamInstTyCon family instTys co_tycon }
    
------------------------------------------------------
mkAbstractTyConRhs :: AlgTyConRhs
mkAbstractTyConRhs = AbstractTyCon

mkDataTyConRhs :: [DataCon] -> AlgTyConRhs
mkDataTyConRhs cons
  = DataTyCon {
        data_cons = cons,
        is_enum = not (null cons) && all is_enum_con cons
		  -- See Note [Enumeration types] in TyCon
    }
  where
    is_enum_con con
       | (_tvs, theta, arg_tys, _res) <- dataConSig con
       = null theta && null arg_tys


mkNewTyConRhs :: Name -> TyCon -> DataCon -> TcRnIf m n AlgTyConRhs
-- ^ Monadic because it makes a Name for the coercion TyCon
--   We pass the Name of the parent TyCon, as well as the TyCon itself,
--   because the latter is part of a knot, whereas the former is not.
mkNewTyConRhs tycon_name tycon con 
  = do	{ co_tycon_name <- newImplicitBinder tycon_name mkNewTyCoOcc
	; let co_tycon = mkNewTypeCo co_tycon_name tycon etad_tvs etad_rhs
	; traceIf (text "mkNewTyConRhs" <+> ppr co_tycon)
	; return (NewTyCon { data_con    = con, 
		       	     nt_rhs      = rhs_ty,
		       	     nt_etad_rhs = (etad_tvs, etad_rhs),
 		       	     nt_co 	 = co_tycon } ) }
                             -- Coreview looks through newtypes with a Nothing
                             -- for nt_co, or uses explicit coercions otherwise
  where
    tvs    = tyConTyVars tycon
    inst_con_ty = applyTys (dataConUserType con) (mkTyVarTys tvs)
    rhs_ty = ASSERT( isFunTy inst_con_ty ) funArgTy inst_con_ty
	-- Instantiate the data con with the 
	-- type variables from the tycon
	-- NB: a newtype DataCon has a type that must look like
	--        forall tvs.  <arg-ty> -> T tvs
	-- Note that we *can't* use dataConInstOrigArgTys here because
	-- the newtype arising from   class Foo a => Bar a where {}
  	-- has a single argument (Foo a) that is a *type class*, so
	-- dataConInstOrigArgTys returns [].

    etad_tvs :: [TyVar]	-- Matched lazily, so that mkNewTypeCo can
    etad_rhs :: Type	-- return a TyCon without pulling on rhs_ty
			-- See Note [Tricky iface loop] in LoadIface
    (etad_tvs, etad_rhs) = eta_reduce (reverse tvs) rhs_ty
 
    eta_reduce :: [TyVar]		-- Reversed
	       -> Type			-- Rhs type
	       -> ([TyVar], Type)	-- Eta-reduced version (tyvars in normal order)
    eta_reduce (a:as) ty | Just (fun, arg) <- splitAppTy_maybe ty,
			   Just tv <- getTyVar_maybe arg,
			   tv == a,
			   not (a `elemVarSet` tyVarsOfType fun)
			 = eta_reduce as fun
    eta_reduce tvs ty = (reverse tvs, ty)
				

------------------------------------------------------
buildDataCon :: Name -> Bool
	    -> [HsBang] 
	    -> [Name]			-- Field labels
	    -> [TyVar] -> [TyVar]	-- Univ and ext 
            -> [(TyVar,Type)]           -- Equality spec
	    -> ThetaType		-- Does not include the "stupid theta"
					-- or the GADT equalities
	    -> [Type] -> Type		-- Argument and result types
	    -> TyCon			-- Rep tycon
	    -> TcRnIf m n DataCon
-- A wrapper for DataCon.mkDataCon that
--   a) makes the worker Id
--   b) makes the wrapper Id if necessary, including
--	allocating its unique (hence monadic)
buildDataCon src_name declared_infix arg_stricts field_lbls
	     univ_tvs ex_tvs eq_spec ctxt arg_tys res_ty rep_tycon
  = do	{ wrap_name <- newImplicitBinder src_name mkDataConWrapperOcc
	; work_name <- newImplicitBinder src_name mkDataConWorkerOcc
	-- This last one takes the name of the data constructor in the source
	-- code, which (for Haskell source anyway) will be in the DataName name
	-- space, and puts it into the VarName name space

	; let
		stupid_ctxt = mkDataConStupidTheta rep_tycon arg_tys univ_tvs
		data_con = mkDataCon src_name declared_infix
				     arg_stricts field_lbls
				     univ_tvs ex_tvs eq_spec ctxt
				     arg_tys res_ty rep_tycon
				     stupid_ctxt dc_ids
		dc_ids = mkDataConIds wrap_name work_name data_con

	; return data_con }


-- The stupid context for a data constructor should be limited to
-- the type variables mentioned in the arg_tys
-- ToDo: Or functionally dependent on?  
--	 This whole stupid theta thing is, well, stupid.
mkDataConStupidTheta :: TyCon -> [Type] -> [TyVar] -> [PredType]
mkDataConStupidTheta tycon arg_tys univ_tvs
  | null stupid_theta = []	-- The common case
  | otherwise 	      = filter in_arg_tys stupid_theta
  where
    tc_subst	 = zipTopTvSubst (tyConTyVars tycon) (mkTyVarTys univ_tvs)
    stupid_theta = substTheta tc_subst (tyConStupidTheta tycon)
	-- Start by instantiating the master copy of the 
	-- stupid theta, taken from the TyCon

    arg_tyvars      = tyVarsOfTypes arg_tys
    in_arg_tys pred = not $ isEmptyVarSet $ 
		      tyVarsOfPred pred `intersectVarSet` arg_tyvars
\end{code}


------------------------------------------------------
\begin{code}
type TcMethInfo = (Name, DefMethSpec, Type)  
        -- A temporary intermediate, to communicate between 
        -- tcClassSigs and buildClass.

buildClass :: Bool		-- True <=> do not include unfoldings 
				--	    on dict selectors
				-- Used when importing a class without -O
	   -> Name -> [TyVar] -> ThetaType
	   -> [FunDep TyVar]		   -- Functional dependencies
	   -> [TyThing]			   -- Associated types
	   -> [TcMethInfo]                 -- Method info
	   -> RecFlag			   -- Info for type constructor
	   -> TcRnIf m n Class

buildClass no_unf class_name tvs sc_theta fds ats sig_stuff tc_isrec
  = do	{ traceIf (text "buildClass")
	; tycon_name <- newImplicitBinder class_name mkClassTyConOcc
	; datacon_name <- newImplicitBinder class_name mkClassDataConOcc
		-- The class name is the 'parent' for this datacon, not its tycon,
		-- because one should import the class to get the binding for 
		-- the datacon

	; fixM (\ rec_clas -> do {	-- Only name generation inside loop

	; op_items <- mapM (mk_op_item rec_clas) sig_stuff
	  		-- Build the selector id and default method id

	; let (eq_theta, dict_theta) = partition isEqPred sc_theta

	      -- We only make selectors for the *value* superclasses, 
	      -- not equality predicates 
	; sc_sel_names <- mapM  (newImplicitBinder class_name . mkSuperDictSelOcc) 
				[1..length dict_theta]
        ; let sc_sel_ids = [ mkDictSelId no_unf sc_name rec_clas 
                           | sc_name <- sc_sel_names]
	      -- We number off the Dict superclass selectors, 1, 2, 3 etc so that we 
	      -- can construct names for the selectors. Thus
	      --      class (C a, C b) => D a b where ...
	      -- gives superclass selectors
	      --      D_sc1, D_sc2
	      -- (We used to call them D_C, but now we can have two different
	      --  superclasses both called C!)
	
	; let use_newtype = null eq_theta && (length dict_theta + length sig_stuff == 1)
		-- Use a newtype if the data constructor has 
		-- 	(a) exactly one value field
		--	(b) no existential or equality-predicate fields
		-- i.e. exactly one operation or superclass taken together
		-- See note [Class newtypes and equality predicates]

		-- We play a bit fast and loose by treating the dictionary
		-- superclasses as ordinary arguments.  That means that in 
                -- the case of
		--     class C a => D a
		-- we don't get a newtype with no arguments!
	      args      = sc_sel_names ++ op_names
	      op_tys	= [ty | (_,_,ty) <- sig_stuff]
	      op_names  = [op | (op,_,_) <- sig_stuff]
	      arg_tys   = map mkPredTy dict_theta ++ op_tys
              rec_tycon = classTyCon rec_clas
               
	; dict_con <- buildDataCon datacon_name
				   False 	-- Not declared infix
				   (map (const HsNoBang) args)
				   [{- No fields -}]
				   tvs [{- no existentials -}]
                                   [{- No GADT equalities -}] 
                                   eq_theta
                                   arg_tys
				   (mkTyConApp rec_tycon (mkTyVarTys tvs))
				   rec_tycon

	; rhs <- if use_newtype
		 then mkNewTyConRhs tycon_name rec_tycon dict_con
		 else return (mkDataTyConRhs [dict_con])

	; let {	clas_kind = mkArrowKinds (map tyVarKind tvs) liftedTypeKind

 	      ; tycon = mkClassTyCon tycon_name clas_kind tvs
 	                             rhs rec_clas tc_isrec
		-- A class can be recursive, and in the case of newtypes 
		-- this matters.  For example
		-- 	class C a where { op :: C b => a -> b -> Int }
		-- Because C has only one operation, it is represented by
		-- a newtype, and it should be a *recursive* newtype.
		-- [If we don't make it a recursive newtype, we'll expand the
		-- newtype like a synonym, but that will lead to an infinite
		-- type]
	      ; atTyCons = [tycon | ATyCon tycon <- ats]

	      ; result = mkClass class_name tvs fds 
			         (eq_theta ++ dict_theta)  -- Equalities first
                                 (length eq_theta)	   -- Number of equalities
                                 sc_sel_ids atTyCons
				 op_items tycon
	      }
	; traceIf (text "buildClass" <+> ppr tycon) 
	; return result
	})}
  where
    mk_op_item :: Class -> TcMethInfo -> TcRnIf n m ClassOpItem
    mk_op_item rec_clas (op_name, dm_spec, _) 
      = do { dm_info <- case dm_spec of
                          NoDM      -> return NoDefMeth
                          GenericDM -> do { dm_name <- newImplicitBinder op_name mkGenDefMethodOcc
			  	          ; return (GenDefMeth dm_name) }
                          VanillaDM -> do { dm_name <- newImplicitBinder op_name mkDefaultMethodOcc
			  	          ; return (DefMeth dm_name) }
           ; return (mkDictSelId no_unf op_name rec_clas, dm_info) }
\end{code}

Note [Class newtypes and equality predicates]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Consider
	class (a ~ F b) => C a b where
	  op :: a -> b

We cannot represent this by a newtype, even though it's not
existential, and there's only one value field, because we do
capture an equality predicate:

	data C a b where
	  MkC :: forall a b. (a ~ F b) => (a->b) -> C a b

We need to access this equality predicate when we get passes a C
dictionary.  See Trac #2238