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

[ghc-hetmet.git] / ghc / compiler / coreSyn / CoreSyn.lhs

diff --git a/ghc/compiler/coreSyn/CoreSyn.lhs b/ghc/compiler/coreSyn/CoreSyn.lhs
index 12f750f..a074499 100644 (file)
--- a/ghc/compiler/coreSyn/CoreSyn.lhs
+++ b/ghc/compiler/coreSyn/CoreSyn.lhs
@@ -79,11 +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
-                               -- 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
@@ -109,6 +125,8 @@ data Note
   | InlineMe           -- Instructs simplifer to treat the enclosed expression
                        -- as very small, and inline it at its call sites
 
+  | CoreNote String     -- A generic core annotation, propagated but not used by GHC
+
 -- NOTE: we also treat expressions wrapped in InlineMe as
 -- 'cheap' and 'dupable' (in the sense of exprIsCheap, exprIsDupable)
 -- What this means is that we obediently inline even things that don't
@@ -549,6 +567,7 @@ seqExprs [] = ()
 seqExprs (e:es) = seqExpr e `seq` seqExprs es
 
 seqNote (Coerce t1 t2) = seqType t1 `seq` seqType t2
+seqNote (CoreNote s)   = s `seq` ()
 seqNote other         = ()
 
 seqBndr b = b `seq` ()