[commit: ghc] master: Comments only (9851275)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/985127510685c3e7ed462260bd69d2e6557430f4/ghc

>---------------------------------------------------------------

commit 985127510685c3e7ed462260bd69d2e6557430f4
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Thu Jul 23 08:34:10 2015 +0100

    Comments only


>---------------------------------------------------------------

985127510685c3e7ed462260bd69d2e6557430f4
 compiler/typecheck/FunDeps.hs | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/compiler/typecheck/FunDeps.hs b/compiler/typecheck/FunDeps.hs
index 9d4ef1c..997dcc0 100644
--- a/compiler/typecheck/FunDeps.hs
+++ b/compiler/typecheck/FunDeps.hs
@@ -225,12 +225,18 @@ checkClsFD :: FunDep TyVar -> [TyVar]             -- One functional dependency f
            -> ClsInst                             -- An instance template
            -> TyVarSet -> [Type] -> [Maybe Name]  -- Arguments of this (C tys) predicate
                                                   -- TyVarSet are extra tyvars that can be instantiated
-           -> [([TyVar], [Pair Type])]
+           -> [([TyVar], [Pair Type])]  -- Empty or singleton
 
 checkClsFD fd clas_tvs
            (ClsInst { is_tvs = qtvs, is_tys = tys_inst, is_tcs = rough_tcs_inst })
            extra_qtvs tys_actual rough_tcs_actual
 
+-- Compare instance   {a,b}   C sx sp sy sq
+--         with       {c,d,e} C tx tp ty tq
+--         for fundep (x,y -> p,q)  from class  (C x p y q)
+-- If (sx,sy) unifies with (tx,ty), take the subst S
+-- 
+
 -- 'qtvs' are the quantified type variables, the ones which an be instantiated
 -- to make the types match.  For example, given
 --      class C a b | a->b where ...