[commit: ghc] master: Comments only (4c571f3)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/4c571f3321eb8f7a06dada4c37822c22bbdd148b/ghc

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

commit 4c571f3321eb8f7a06dada4c37822c22bbdd148b
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Jul 25 17:50:28 2018 +0100

    Comments only


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

4c571f3321eb8f7a06dada4c37822c22bbdd148b
 compiler/deSugar/DsBinds.hs     |  5 +++--
 compiler/typecheck/TcRnTypes.hs | 12 +++++++++---
 2 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/compiler/deSugar/DsBinds.hs b/compiler/deSugar/DsBinds.hs
index db7acfd..6524e10 100644
--- a/compiler/deSugar/DsBinds.hs
+++ b/compiler/deSugar/DsBinds.hs
@@ -184,8 +184,9 @@ dsHsBind dflags (AbsBinds { abs_tvs = tyvars, abs_ev_vars = dicts
                           , abs_binds = binds, abs_sig = has_sig })
   = do { ds_binds <- addDictsDs (listToBag dicts) $
                      dsLHsBinds binds
-                                   -- addDictsDs: push type constraints deeper
-                                   --             for inner pattern match check
+                         -- addDictsDs: push type constraints deeper
+                         --             for inner pattern match check
+                         -- See Check, Note [Type and Term Equality Propagation]
 
        ; ds_ev_binds <- dsTcEvBinds_s ev_binds
 
diff --git a/compiler/typecheck/TcRnTypes.hs b/compiler/typecheck/TcRnTypes.hs
index e8f0762..6627c25 100644
--- a/compiler/typecheck/TcRnTypes.hs
+++ b/compiler/typecheck/TcRnTypes.hs
@@ -385,9 +385,15 @@ instance ContainsModule DsGblEnv where
 data DsLclEnv = DsLclEnv {
         dsl_meta    :: DsMetaEnv,        -- Template Haskell bindings
         dsl_loc     :: RealSrcSpan,      -- To put in pattern-matching error msgs
-        dsl_dicts   :: Bag EvVar,        -- Constraints from GADT pattern-matching
-        dsl_tm_cs   :: Bag SimpleEq,
-        dsl_pm_iter :: IORef Int         -- no iterations for pmcheck
+
+        -- See Note [Note [Type and Term Equality Propagation] in Check.hs
+        -- These two fields are augmented as we walk inwards,
+        -- through each patttern match in turn
+        dsl_dicts   :: Bag EvVar,     -- Constraints from GADT pattern-matching
+        dsl_tm_cs   :: Bag SimpleEq,  -- Constraints form term-level pattern matching
+
+        dsl_pm_iter :: IORef Int  -- Number of iterations for pmcheck so far
+                                  -- We fail if this gets too big
      }
 
 -- Inside [| |] brackets, the desugarer looks