From: simonpj <unknown>
Date: Tue, 29 Jul 2003 10:15:10 +0000 (+0000)
Subject: [project @ 2003-07-29 10:14:57 by simonpj]
X-Git-Tag: Approx_11550_changesets_converted~616
X-Git-Url: http://git.megacz.com/?a=commitdiff_plain;ds=sidebyside;h=1a03162e0239a336d297383107a68d06814e8924;p=ghc-hetmet.git

[project @ 2003-07-29 10:14:57 by simonpj]
Comments only
---

diff --git a/ghc/compiler/coreSyn/CoreSyn.lhs b/ghc/compiler/coreSyn/CoreSyn.lhs
index 4c70bb3..a074499 100644
--- a/ghc/compiler/coreSyn/CoreSyn.lhs
+++ b/ghc/compiler/coreSyn/CoreSyn.lhs
@@ -79,12 +79,27 @@ data Expr b	-- "b" for the type of binders,
   | Lam   b (Expr b)
   | Let   (Bind b) (Expr b)
   | Case  (Expr b) b [Alt b]  	-- Binder gets bound to value of scrutinee
-	-- Invariant: the list of alternatives is ALWAYS EXHAUSTIVE
-	-- Invariant: the DEFAULT case must be *first*, if it occurs at all
+	-- Invariant: The list of alternatives is ALWAYS EXHAUSTIVE,
+	--	      meaning that it covers all cases that can occur
+	--	      See the example below
+	--
+	-- Invariant: The DEFAULT case must be *first*, if it occurs at all
   | Note  Note (Expr b)
   | Type  Type			-- This should only show up at the top
 				-- level of an Arg
 
+-- An "exhausive" case does not necessarily mention all constructors:
+--	data Foo = Red | Green | Blue
+--
+--	...case x of 
+--		Red   -> True
+--		other -> f (case x of 
+--				Green -> ...
+--				Blue  -> ... )
+-- The inner case does not need a Red alternative, because x can't be Red at
+-- that program point.
+
+
 type Arg b = Expr b		-- Can be a Type
 
 type Alt b = (AltCon, [b], Expr b)	-- (DEFAULT, [], rhs) is the default alternative
diff --git a/ghc/compiler/typecheck/TcDeriv.lhs b/ghc/compiler/typecheck/TcDeriv.lhs
index 9ea0190..60b7b2f 100644
--- a/ghc/compiler/typecheck/TcDeriv.lhs
+++ b/ghc/compiler/typecheck/TcDeriv.lhs
@@ -497,6 +497,11 @@ makeDerivEqns tycl_decls
 						-- Don't want
 						--	instance Eq [A] => Eq A !!
 
+			-- Here's a recursive newtype that's actually OK
+			--	newtype S1 = S1 [T1 ()]
+			--	newtype T1 a = T1 (StateT S1 IO a ) deriving( Monad )
+			-- It's currently rejected.  Oh well.
+
 	-- Check that eta reduction is OK
 	-- 	(a) the dropped-off args are identical
 	--	(b) the remaining type args mention