X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FdeSugar%2FMatchCon.lhs;h=141f6a7e3dcb56609ecb1be3274efa7c2ffb3b30;hb=0e7803679c313842bd9a6fc9deba7809760ccd62;hp=152d082050ee212ca89fa7329acec8c118c68278;hpb=9dd6e1c216993624a2cd74b62ca0f0569c02c26b;p=ghc-hetmet.git

diff --git a/ghc/compiler/deSugar/MatchCon.lhs b/ghc/compiler/deSugar/MatchCon.lhs
index 152d082..141f6a7 100644
--- a/ghc/compiler/deSugar/MatchCon.lhs
+++ b/ghc/compiler/deSugar/MatchCon.lhs
@@ -1,5 +1,5 @@
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 %
 \section[MatchCon]{Pattern-matching constructors}
 
@@ -10,14 +10,17 @@ module MatchCon ( matchConFamily ) where
 
 import {-# SOURCE #-} Match	( match )
 
-import HsSyn		( OutPat(..), HsLit, HsExpr )
-import DsHsSyn		( outPatType )
+import HsSyn		( Pat(..), HsConDetails(..) )
 
 import DsMonad
 import DsUtils
 
-import Id		( GenId{-instances-}, Id )
-import Util		( panic, assertPanic )
+import Id		( Id )
+import Subst		( mkSubst, mkInScopeSet, bindSubst, substExpr )
+import CoreFVs		( exprFreeVars )
+import VarEnv		( emptySubstEnv )
+import ListSetOps	( equivClassesByUniq )
+import Unique		( Uniquable(..) )
 \end{code}
 
 We are confronted with the first column of patterns in a set of
@@ -76,51 +79,61 @@ matchConFamily :: [Id]
 	       -> DsM MatchResult
 
 matchConFamily (var:vars) eqns_info
-  = match_cons_used vars eqns_info `thenDs` \ alts ->
-    mkCoAlgCaseMatchResult var alts
+  = let
+	-- Sort into equivalence classes by the unique on the constructor
+	-- All the EqnInfos should start with a ConPat
+	eqn_groups = equivClassesByUniq get_uniq eqns_info
+	get_uniq (EqnInfo _ _ (ConPatOut data_con _ _ _ _ : _) _) = getUnique data_con
+    in
+	-- Now make a case alternative out of each group
+    mapDs (match_con vars) eqn_groups	`thenDs` \ alts ->
+
+    returnDs (mkCoAlgCaseMatchResult var alts)
 \end{code}
 
 And here is the local function that does all the work.  It is
 more-or-less the @matchCon@/@matchClause@ functions on page~94 in
 Wadler's chapter in SLPJ.
-\begin{code}
-match_cons_used _ [{- no more eqns -}] = returnDs []
 
-match_cons_used vars eqns_info@(EqnInfo n ctx (ConPat data_con _ arg_pats : ps1) _ : eqns)
-  = let
-	(eqns_for_this_con, eqns_not_for_this_con)       = splitByCon eqns_info
-    in
-    -- Go ahead and do the recursive call to make the alts
-    -- for the other ConPats in this con family...
-    match_cons_used vars eqns_not_for_this_con 	          `thenDs` \ rest_of_alts ->
-
-    -- Make new vars for the con arguments; avoid new locals where possible
-    selectMatchVars arg_pats				   `thenDs` \ new_vars ->
+\begin{code}
+match_con vars (eqn1@(EqnInfo _ _ (ConPatOut data_con (PrefixCon arg_pats) _ ex_tvs ex_dicts : _) _)
+		: other_eqns)
+  = -- Make new vars for the con arguments; avoid new locals where possible
+    mapDs selectMatchVar arg_pats	`thenDs` \ arg_vars ->
 
     -- Now do the business to make the alt for _this_ ConPat ...
-    match (new_vars++vars)
-	  (map shift_con_pat eqns_for_this_con)		   `thenDs` \ match_result ->
-
-    returnDs (
-	(data_con, new_vars, match_result)
-	: rest_of_alts
-    )
+    match (arg_vars ++ vars) 
+	  (map shift_con_pat (eqn1:other_eqns))	`thenDs` \ match_result ->
+
+    --		[See "notes on do_subst" below this function]
+    -- Make the ex_tvs and ex_dicts line up with those
+    -- in the first pattern.  Remember, they are all guaranteed to be variables
+    let
+	match_result' | null ex_tvs     = match_result
+		      | null other_eqns = match_result
+		      | otherwise       = adjustMatchResult do_subst match_result
+    in
+	
+    returnDs (data_con, ex_tvs ++ ex_dicts ++ arg_vars, match_result')
   where
-    splitByCon :: [EquationInfo] -> ([EquationInfo], [EquationInfo])
-    splitByCon [] = ([],[])
-    splitByCon (info@(EqnInfo _ _ (pat : _) _) : rest)
-	= case pat of
-		ConPat n _ _ | n == data_con -> (info:rest_yes, rest_no)
-		other_pat		     -> (rest_yes,      info:rest_no)
-	where
-	  (rest_yes, rest_no) = splitByCon rest
-
     shift_con_pat :: EquationInfo -> EquationInfo
-    shift_con_pat (EqnInfo n ctx (ConPat _ _ pats': pats) match_result)
-      = EqnInfo n ctx (pats' ++ pats) match_result
-    shift_con_pat (EqnInfo n ctx (WildPat _: pats) match_result) -- Will only happen in shadow
-      = EqnInfo n ctx ([WildPat (outPatType arg_pat) | arg_pat <- arg_pats] ++ pats) match_result
-    shift_con_pat other = panic "matchConFamily:match_cons_used:shift_con_pat"
+    shift_con_pat (EqnInfo n ctx (ConPatOut _ (PrefixCon arg_pats) _ _ _ : pats) match_result)
+      = EqnInfo n ctx (arg_pats ++ pats) match_result
+
+    other_pats = [p | EqnInfo _ _ (p:_) _ <- other_eqns]
+
+    var_prs = concat [ (ex_tvs'   `zip` ex_tvs) ++ 
+		       (ex_dicts' `zip` ex_dicts) 
+		     | ConPatOut _ _ _ ex_tvs' ex_dicts' <- other_pats ]
+
+    do_subst e = substExpr subst e
+	       where
+		 subst    = foldl (\ s (v', v) -> bindSubst s v' v) in_scope var_prs
+		 in_scope = mkSubst (mkInScopeSet (exprFreeVars e)) emptySubstEnv
+			-- We put all the free variables of e into the in-scope 
+			-- set of the substitution, not because it is necessary,
+			-- but to suppress the warning in Subst.lookupInScope
+			-- Tiresome, but doing the substitution at all is rare.
 \end{code}
 
 Note on @shift_con_pats@ just above: does what the list comprehension in
@@ -128,3 +141,37 @@ Note on @shift_con_pats@ just above: does what the list comprehension in
 life.  Works for @ConPats@, and we want it to fail catastrophically
 for anything else (which a list comprehension wouldn't).
 Cf.~@shift_lit_pats@ in @MatchLits@.
+
+
+Notes on do_subst stuff
+~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+	data T = forall a. Ord a => T a (a->Int)
+
+	f (T x f) True  = ...expr1...
+	f (T y g) False = ...expr2..
+
+When we put in the tyvars etc we get
+
+	f (T a (d::Ord a) (x::a) (f::a->Int)) True =  ...expr1...
+	f (T b (e::Ord a) (y::a) (g::a->Int)) True =  ...expr2...
+
+After desugaring etc we'll get a single case:
+
+	f = \t::T b::Bool -> 
+	    case t of
+	       T a (d::Ord a) (x::a) (f::a->Int)) ->
+	    case b of
+		True  -> ...expr1...
+		False -> ...expr2...
+
+*** We have to substitute [a/b, d/e] in expr2! **
+That is what do_subst is doing.
+
+Originally I tried to use 
+	(\b -> let e = d in expr2) a 
+to do this substitution.  While this is "correct" in a way, it fails
+Lint, because e::Ord b but d::Ord a.  
+
+So now I simply do the substitution properly using substExpr.
+