module Vectorise.Monad.InstEnv (
	lookupInst,
	lookupFamInst
) where
import Vectorise.Monad.Global
import Vectorise.Monad.Base
import Vectorise.Env

import FamInstEnv
import InstEnv
import Class
import Type
import TyCon
import Outputable


#include "HsVersions.h"


getInstEnv :: VM (InstEnv, InstEnv)
getInstEnv = readGEnv global_inst_env

getFamInstEnv :: VM FamInstEnvs
getFamInstEnv = readGEnv global_fam_inst_env


-- Look up the dfun of a class instance.
--
-- The match must be unique - ie, match exactly one instance - but the 
-- type arguments used for matching may be more specific than those of 
-- the class instance declaration.  The found class instances must not have
-- any type variables in the instance context that do not appear in the
-- instances head (i.e., no flexi vars); for details for what this means,
-- see the docs at InstEnv.lookupInstEnv.
--
lookupInst :: Class -> [Type] -> VM (DFunId, [Type])
lookupInst cls tys
  = do { instEnv <- getInstEnv
       ; case lookupInstEnv instEnv cls tys of
	   ([(inst, inst_tys)], _) 
             | noFlexiVar -> return (instanceDFunId inst, inst_tys')
             | otherwise  -> pprPanic "VectMonad.lookupInst: flexi var: " 
                                      (ppr $ mkTyConApp (classTyCon cls) tys)
             where
               inst_tys'  = [ty | Right ty <- inst_tys]
               noFlexiVar = all isRight inst_tys
	   _other         ->
             pprPanic "VectMonad.lookupInst: not found " (ppr cls <+> ppr tys)
       }
  where
    isRight (Left  _) = False
    isRight (Right _) = True

-- Look up the representation tycon of a family instance.
--
-- The match must be unique - ie, match exactly one instance - but the 
-- type arguments used for matching may be more specific than those of 
-- the family instance declaration.
--
-- Return the instance tycon and its type instance.  For example, if we have
--
--  lookupFamInst 'T' '[Int]' yields (':R42T', 'Int')
--
-- then we have a coercion (ie, type instance of family instance coercion)
--
--  :Co:R42T Int :: T [Int] ~ :R42T Int
--
-- which implies that :R42T was declared as 'data instance T [a]'.
--
lookupFamInst :: TyCon -> [Type] -> VM (TyCon, [Type])
lookupFamInst tycon tys
  = ASSERT( isOpenTyCon tycon )
    do { instEnv <- getFamInstEnv
       ; case lookupFamInstEnv instEnv tycon tys of
	   [(fam_inst, rep_tys)] -> return (famInstTyCon fam_inst, rep_tys)
	   _other                -> 
             pprPanic "VectMonad.lookupFamInst: not found: " 
                      (ppr $ mkTyConApp tycon tys)
       }