From a1fc7ce3f16e302b19ab39174ee065fa116b6afd Mon Sep 17 00:00:00 2001
From: Simon Peyton Jones <simonpj@microsoft.com>
Date: Fri, 29 Sep 2017 11:39:28 +0100
Subject: [PATCH] Comments only

---
 compiler/prelude/PrelRules.hs      | 17 +++++++++--------
 compiler/stranal/WorkWrap.hs       |  2 +-
 compiler/typecheck/TcTyClsDecls.hs |  2 +-
 3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/compiler/prelude/PrelRules.hs b/compiler/prelude/PrelRules.hs
index 810fd2ba60..8838c4aaff 100644
--- a/compiler/prelude/PrelRules.hs
+++ b/compiler/prelude/PrelRules.hs
@@ -897,21 +897,22 @@ tagToEnumRule = do
     _ -> WARN( True, text "tagToEnum# on non-enumeration type" <+> ppr ty )
          return $ mkRuntimeErrorApp rUNTIME_ERROR_ID ty "tagToEnum# on non-enumeration type"
 
-{-
-For dataToTag#, we can reduce if either
-
-        (a) the argument is a constructor
-        (b) the argument is a variable whose unfolding is a known constructor
--}
-
+------------------------------
 dataToTagRule :: RuleM CoreExpr
+-- Rules for dataToTag#
 dataToTagRule = a `mplus` b
   where
+    -- dataToTag (tagToEnum x)   ==>   x
     a = do
       [Type ty1, Var tag_to_enum `App` Type ty2 `App` tag] <- getArgs
       guard $ tag_to_enum `hasKey` tagToEnumKey
       guard $ ty1 `eqType` ty2
-      return tag -- dataToTag (tagToEnum x)   ==>   x
+      return tag
+
+    -- dataToTag (K e1 e2)  ==>   tag-of K
+    -- This also works (via exprIsConApp_maybe) for
+    --   dataToTag x
+    -- where x's unfolding is a constructor application
     b = do
       dflags <- getDynFlags
       [_, val_arg] <- getArgs
diff --git a/compiler/stranal/WorkWrap.hs b/compiler/stranal/WorkWrap.hs
index 28b0df3404..ac8798e56e 100644
--- a/compiler/stranal/WorkWrap.hs
+++ b/compiler/stranal/WorkWrap.hs
@@ -182,7 +182,7 @@ If we have
 
 where f is strict in y, we might get a more efficient loop by w/w'ing
 f.  But that would make a new unfolding which would overwrite the old
-one! So the function would no longer be ININABLE, and in particular
+one! So the function would no longer be INLNABLE, and in particular
 will not be specialised at call sites in other modules.
 
 This comes in practice (Trac #6056).
diff --git a/compiler/typecheck/TcTyClsDecls.hs b/compiler/typecheck/TcTyClsDecls.hs
index 876784378c..fa8b2bbdc2 100644
--- a/compiler/typecheck/TcTyClsDecls.hs
+++ b/compiler/typecheck/TcTyClsDecls.hs
@@ -3002,7 +3002,7 @@ checkValidRoleAnnots role_annots tc
           ; _ <- zipWith3M checkRoleAnnot vis_vars the_role_annots vis_roles
           -- Representational or phantom roles for class parameters
           -- quickly lead to incoherence. So, we require
-          -- IncoherentInstances to have them. See #8773.
+          -- IncoherentInstances to have them. See #8773, #14292
           ; incoherent_roles_ok <- xoptM LangExt.IncoherentInstances
           ; checkTc (  incoherent_roles_ok
                     || (not $ isClassTyCon tc)
-- 
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