path: root/compiler/types/Class.lhs

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

The @Class@ datatype

\begin{code}
{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

module Class (
	Class,
        ClassOpItem, DefMeth (..),
        ClassATItem, ATDefault (..),
	defMethSpecOfDefMeth,

	FunDep,	pprFundeps, pprFunDep,

	mkClass, classTyVars, classArity, 
	classKey, className, classATs, classATItems, classTyCon, classMethods,
	classOpItems, classBigSig, classExtraBigSig, classTvsFds, classSCTheta,
        classAllSelIds, classSCSelId
    ) where

#include "Typeable.h"
#include "HsVersions.h"

import {-# SOURCE #-} TyCon	( TyCon, tyConName, tyConUnique )
import {-# SOURCE #-} TypeRep	( Type, PredType )

import Var
import Name
import BasicTypes
import Unique
import Util
import Outputable
import SrcLoc
import FastString

import Data.Typeable (Typeable)
import qualified Data.Data as Data
\end{code}

%************************************************************************
%*									*
\subsection[Class-basic]{@Class@: basic definition}
%*									*
%************************************************************************

A @Class@ corresponds to a Greek kappa in the static semantics:

\begin{code}
data Class
  = Class {
	classTyCon :: TyCon,	-- The data type constructor for
				-- dictionaries of this class
                                -- See Note [ATyCon for classes] in TypeRep

	className :: Name,              -- Just the cached name of the TyCon
	classKey  :: Unique,		-- Cached unique of TyCon
	
	classTyVars  :: [TyVar],	-- The class kind and type variables;
		     			-- identical to those of the TyCon

	classFunDeps :: [FunDep TyVar],	-- The functional dependencies

	-- Superclasses: eg: (F a ~ b, F b ~ G a, Eq a, Show b)
        -- We need value-level selectors for both the dictionary 
	-- superclasses and the equality superclasses
	classSCTheta :: [PredType],	-- Immediate superclasses, 
	classSCSels  :: [Id],		-- Selector functions to extract the
		     			--   superclasses from a 
					--   dictionary of this class
	-- Associated types
        classATStuff :: [ClassATItem],	-- Associated type families

        -- Class operations (methods, not superclasses)
	classOpStuff :: [ClassOpItem]	-- Ordered by tag
     }
  deriving Typeable

type FunDep a = ([a],[a])  --  e.g. class C a b c | a b -> c, a c -> b where...
			   --  Here fun-deps are [([a,b],[c]), ([a,c],[b])]

type ClassOpItem = (Id, DefMeth)
        -- Selector function; contains unfolding
	-- Default-method info

data DefMeth = NoDefMeth 		-- No default method
	     | DefMeth Name  		-- A polymorphic default method
	     | GenDefMeth Name 		-- A generic default method
             deriving Eq

type ClassATItem = (TyCon, [ATDefault])
  -- Default associated types from these templates. If the template list is empty,
  -- we assume that there is no default -- not that the default is to generate no
  -- instances (this only makes a difference for warnings).
  -- We can have more than one default per type; see
  -- Note [Associated type defaults] in TcTyClsDecls

-- Each associated type default template is a triple of:
data ATDefault = ATD { -- TyVars of the RHS and family arguments 
                       -- (including, but perhaps more than, the class TVs)
                       atDefaultTys     :: [TyVar],
                       -- The instantiated family arguments
                       atDefaultPats    :: [Type],
                       -- The RHS of the synonym
                       atDefaultRhs     :: Type,
                       -- The source location of the synonym
                       atDefaultSrcSpan :: SrcSpan }

-- | Convert a `DefMethSpec` to a `DefMeth`, which discards the name field in
--   the `DefMeth` constructor of the `DefMeth`.
defMethSpecOfDefMeth :: DefMeth -> DefMethSpec
defMethSpecOfDefMeth meth
 = case meth of
	NoDefMeth	-> NoDM
	DefMeth _	-> VanillaDM
	GenDefMeth _	-> GenericDM

\end{code}

The @mkClass@ function fills in the indirect superclasses.

\begin{code}
mkClass :: [TyVar]
	-> [([TyVar], [TyVar])]
	-> [PredType] -> [Id]
	-> [ClassATItem]
	-> [ClassOpItem]
	-> TyCon
	-> Class

mkClass tyvars fds super_classes superdict_sels at_stuff
	op_stuff tycon
  = Class {	classKey     = tyConUnique tycon, 
		className    = tyConName tycon,
		classTyVars  = tyvars,
		classFunDeps = fds,
		classSCTheta = super_classes,
		classSCSels  = superdict_sels,
		classATStuff = at_stuff,
		classOpStuff = op_stuff,
		classTyCon   = tycon }
\end{code}

%************************************************************************
%*									*
\subsection[Class-selectors]{@Class@: simple selectors}
%*									*
%************************************************************************

The rest of these functions are just simple selectors.

\begin{code}
classArity :: Class -> Arity
classArity clas = length (classTyVars clas)
	-- Could memoise this

classAllSelIds :: Class -> [Id]
-- Both superclass-dictionary and method selectors
classAllSelIds c@(Class {classSCSels = sc_sels})
  = sc_sels ++ classMethods c

classSCSelId :: Class -> Int -> Id
-- Get the n'th superclass selector Id
-- where n is 0-indexed, and counts 
--    *all* superclasses including equalities
classSCSelId (Class { classSCSels = sc_sels }) n
  = ASSERT( n >= 0 && n < length sc_sels )
    sc_sels !! n

classMethods :: Class -> [Id]
classMethods (Class {classOpStuff = op_stuff})
  = [op_sel | (op_sel, _) <- op_stuff]

classOpItems :: Class -> [ClassOpItem]
classOpItems = classOpStuff

classATs :: Class -> [TyCon]
classATs (Class { classATStuff = at_stuff })
  = [tc | (tc, _) <- at_stuff]

classATItems :: Class -> [ClassATItem]
classATItems = classATStuff

classTvsFds :: Class -> ([TyVar], [FunDep TyVar])
classTvsFds c
  = (classTyVars c, classFunDeps c)

classBigSig :: Class -> ([TyVar], [PredType], [Id], [ClassOpItem])
classBigSig (Class {classTyVars = tyvars, classSCTheta = sc_theta, 
	 	    classSCSels = sc_sels, classOpStuff = op_stuff})
  = (tyvars, sc_theta, sc_sels, op_stuff)

classExtraBigSig :: Class -> ([TyVar], [FunDep TyVar], [PredType], [Id], [ClassATItem], [ClassOpItem])
classExtraBigSig (Class {classTyVars = tyvars, classFunDeps = fundeps,
			 classSCTheta = sc_theta, classSCSels = sc_sels,
			 classATStuff = ats, classOpStuff = op_stuff})
  = (tyvars, fundeps, sc_theta, sc_sels, ats, op_stuff)
\end{code}


%************************************************************************
%*									*
\subsection[Class-instances]{Instance declarations for @Class@}
%*									*
%************************************************************************

We compare @Classes@ by their keys (which include @Uniques@).

\begin{code}
instance Eq Class where
    c1 == c2 = classKey c1 == classKey c2
    c1 /= c2 = classKey c1 /= classKey c2

instance Ord Class where
    c1 <= c2 = classKey c1 <= classKey c2
    c1 <  c2 = classKey c1 <  classKey c2
    c1 >= c2 = classKey c1 >= classKey c2
    c1 >  c2 = classKey c1 >  classKey c2
    compare c1 c2 = classKey c1 `compare` classKey c2
\end{code}

\begin{code}
instance Uniquable Class where
    getUnique c = classKey c

instance NamedThing Class where
    getName clas = className clas

instance Outputable Class where
    ppr c = ppr (getName c)

instance Show Class where
    showsPrec p c = showsPrecSDoc p (ppr c)

instance Outputable DefMeth where
    ppr (DefMeth n)    =  ptext (sLit "Default method") <+> ppr n
    ppr (GenDefMeth n) =  ptext (sLit "Generic default method") <+> ppr n
    ppr NoDefMeth      =  empty   -- No default method

pprFundeps :: Outputable a => [FunDep a] -> SDoc
pprFundeps []  = empty
pprFundeps fds = hsep (ptext (sLit "|") : punctuate comma (map pprFunDep fds))

pprFunDep :: Outputable a => FunDep a -> SDoc
pprFunDep (us, vs) = hsep [interppSP us, ptext (sLit "->"), interppSP vs]

instance Data.Data Class where
    -- don't traverse?
    toConstr _   = abstractConstr "Class"
    gunfold _ _  = error "gunfold"
    dataTypeOf _ = mkNoRepType "Class"
\end{code}