Add comment for the invariant that DataAlt is never a newtype

diff --git a/compiler/coreSyn/CoreSyn.lhs b/compiler/coreSyn/CoreSyn.lhs
index f83845f..a108945 100644 (file)
--- a/compiler/coreSyn/CoreSyn.lhs
+++ b/compiler/coreSyn/CoreSyn.lhs
@@ -112,7 +112,8 @@ type Arg b = Expr b         -- Can be a Type
 
 type Alt b = (AltCon, [b], Expr b)     -- (DEFAULT, [], rhs) is the default alternative
 
-data AltCon = DataAlt DataCon
+data AltCon = DataAlt DataCon  -- Invariant: the DataCon is always from 
+                               -- a *data* type, and never from a *newtype*
            | LitAlt  Literal
            | DEFAULT
         deriving (Eq, Ord)