fix bugs, add boolean flag to identify coercion variables

[ghc-hetmet.git] / compiler / deSugar / Match.lhs

diff --git a/compiler/deSugar/Match.lhs b/compiler/deSugar/Match.lhs
index 2d64633..9ff1548 100644 (file)
--- a/compiler/deSugar/Match.lhs
+++ b/compiler/deSugar/Match.lhs
@@ -254,7 +254,7 @@ match :: [Id]                 -- Variables rep'ing the exprs we're matching with
       -> DsM MatchResult  -- Desugared result!
 
 match [] ty eqns
-  = ASSERT( not (null eqns) )
+  = ASSERT2( not (null eqns), ppr ty )
     returnDs (foldr1 combineMatchResults match_results)
   where
     match_results = [ ASSERT( null (eqn_pats eqn) ) 
@@ -715,6 +715,9 @@ data PatGroup
 
 
 groupEquations :: [EquationInfo] -> [[(PatGroup, EquationInfo)]]
+-- If the result is of form [g1, g2, g3], 
+-- (a) all the (pg,eq) pairs in g1 have the same pg
+-- (b) none of the gi are empty
 groupEquations eqns
   = runs same_gp [(patGroup (firstPat eqn), eqn) | eqn <- eqns]
   where
@@ -745,6 +748,10 @@ sameGroup (PgN l1)   (PgN l2)   = True             -- Needs conditionals
 sameGroup (PgNpK l1) (PgNpK l2) = l1==l2       -- Order is significant
                                                -- See Note [Order of n+k]
 sameGroup (PgCo        t1)  (PgCo t2)  = t1 `coreEqType` t2
+       -- CoPats are in the same goup only if the type of the
+       -- enclosed pattern is the same. The patterns outside the CoPat
+       -- always have the same type, so this boils down to saying that
+       -- the two coercions are identical.
 sameGroup _          _          = False
  
 patGroup :: Pat Id -> PatGroup