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