{-# OPTIONS -fno-warn-incomplete-patterns #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details

module MatchCon ( matchConFamily ) where

#include "HsVersions.h"

import {-# SOURCE #-} Match	( match )

import HsSyn
import DsBinds
import DataCon
import TcType
import DsMonad
import DsUtils
import Util	( all2, takeList, zipEqual )
import ListSetOps ( runs )
import Id
import Var      ( Var )
import NameEnv
import SrcLoc
import Outputable

matchConFamily :: [Id]
               -> Type
	       -> [[EquationInfo]]
	       -> DsM MatchResult
-- Each group of eqns is for a single constructor
matchConFamily (var:vars) ty groups
  = do	{ alts <- mapM (matchOneCon vars ty) groups
	; return (mkCoAlgCaseMatchResult var ty alts) }

type ConArgPats = HsConDetails (LPat Id) (HsRecFields Id (LPat Id))

matchOneCon :: [Id]
            -> Type
            -> [EquationInfo]
            -> DsM (DataCon, [Var], MatchResult)
matchOneCon vars ty (eqn1 : eqns)	-- All eqns for a single constructor
  = do	{ arg_vars <- selectConMatchVars arg_tys args1
	 	-- Use the first equation as a source of 
		-- suggestions for the new variables

	-- Divide into sub-groups; see Note [Record patterns]
        ; let groups :: [[(ConArgPats, EquationInfo)]]
	      groups = runs compatible_pats [ (pat_args (firstPat eqn), eqn) 
	      	       	    	            | eqn <- eqn1:eqns ]

	; match_results <- mapM (match_group arg_vars) groups

      	; return (con1, tvs1 ++ dicts1 ++ arg_vars, 
		  foldr1 combineMatchResults match_results) }
  where
    ConPatOut { pat_con = L _ con1, pat_ty = pat_ty1,
	        pat_tvs = tvs1, pat_dicts = dicts1, pat_args = args1 }
	      = firstPat eqn1
    fields1 = dataConFieldLabels con1
	
    arg_tys  = dataConInstOrigArgTys con1 inst_tys
    inst_tys = tcTyConAppArgs pat_ty1 ++ 
	       mkTyVarTys (takeList (dataConExTyVars con1) tvs1)
	-- Newtypes opaque, hence tcTyConAppArgs
	-- dataConInstOrigArgTys takes the univ and existential tyvars
	-- and returns the types of the *value* args, which is what we want

    match_group :: [Id] -> [(ConArgPats, EquationInfo)] -> DsM MatchResult
    -- All members of the group have compatible ConArgPats
    match_group arg_vars arg_eqn_prs
      = do { (wraps, eqns') <- mapAndUnzipM shift arg_eqn_prs
    	   ; let group_arg_vars = select_arg_vars arg_vars arg_eqn_prs
    	   ; match_result <- match (group_arg_vars ++ vars) ty eqns'
    	   ; return (adjustMatchResult (foldr1 (.) wraps) match_result) }

    shift (_, eqn@(EqnInfo { eqn_pats = ConPatOut{ pat_tvs = tvs, pat_dicts = ds, 
					           pat_binds = bind, pat_args = args
					} : pats }))
      = do { ds_ev_binds <- dsTcEvBinds bind
	   ; return (wrapBinds (tvs `zip` tvs1) 
		    . wrapBinds (ds  `zip` dicts1)
		    . wrapDsEvBinds ds_ev_binds,
		    eqn { eqn_pats = conArgPats arg_tys args ++ pats }) }

    -- Choose the right arg_vars in the right order for this group
    -- Note [Record patterns]
    select_arg_vars arg_vars ((arg_pats, _) : _)
      | RecCon flds <- arg_pats
      , let rpats = rec_flds flds  
      , not (null rpats)     -- Treated specially; cf conArgPats
      = ASSERT2( length fields1 == length arg_vars, 
                 ppr con1 $$ ppr fields1 $$ ppr arg_vars )
        map lookup_fld rpats
      | otherwise
      = arg_vars
      where
        fld_var_env = mkNameEnv $ zipEqual "get_arg_vars" fields1 arg_vars
	lookup_fld rpat = lookupNameEnv_NF fld_var_env 
		   	  		   (idName (unLoc (hsRecFieldId rpat)))

-----------------
compatible_pats :: (ConArgPats,a) -> (ConArgPats,a) -> Bool
-- Two constructors have compatible argument patterns if the number
-- and order of sub-matches is the same in both cases
compatible_pats (RecCon flds1, _) (RecCon flds2, _) = same_fields flds1 flds2
compatible_pats (RecCon flds1, _) _                 = null (rec_flds flds1)
compatible_pats _                 (RecCon flds2, _) = null (rec_flds flds2)
compatible_pats _                 _                 = True -- Prefix or infix con

same_fields :: HsRecFields Id (LPat Id) -> HsRecFields Id (LPat Id) -> Bool
same_fields flds1 flds2 
  = all2 (\f1 f2 -> unLoc (hsRecFieldId f1) == unLoc (hsRecFieldId f2))
	 (rec_flds flds1) (rec_flds flds2)


-----------------
selectConMatchVars :: [Type] -> ConArgPats -> DsM [Id]
selectConMatchVars arg_tys (RecCon {})      = newSysLocalsDs arg_tys
selectConMatchVars _       (PrefixCon ps)   = selectMatchVars (map unLoc ps)
selectConMatchVars _       (InfixCon p1 p2) = selectMatchVars [unLoc p1, unLoc p2]

conArgPats :: [Type]	-- Instantiated argument types 
			-- Used only to fill in the types of WildPats, which
			-- are probably never looked at anyway
	   -> ConArgPats
	   -> [Pat Id]
conArgPats _arg_tys (PrefixCon ps)   = map unLoc ps
conArgPats _arg_tys (InfixCon p1 p2) = [unLoc p1, unLoc p2]
conArgPats  arg_tys (RecCon (HsRecFields { rec_flds = rpats }))
  | null rpats = map WildPat arg_tys
	-- Important special case for C {}, which can be used for a 
 	-- datacon that isn't declared to have fields at all
  | otherwise  = map (unLoc . hsRecFieldArg) rpats