[commit: ghc] master: Comments only (6d40470)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/6d404707e533922c26aebb82cf97565fe773ca60/ghc

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

commit 6d404707e533922c26aebb82cf97565fe773ca60
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Fri Nov 21 13:29:42 2014 +0000

    Comments only


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

6d404707e533922c26aebb82cf97565fe773ca60
 compiler/typecheck/TcFlatten.lhs |  7 +++++--
 compiler/typecheck/TcSMonad.lhs  | 30 ++----------------------------
 2 files changed, 7 insertions(+), 30 deletions(-)

diff --git a/compiler/typecheck/TcFlatten.lhs b/compiler/typecheck/TcFlatten.lhs
index fbb4729..ac68ec9 100644
--- a/compiler/typecheck/TcFlatten.lhs
+++ b/compiler/typecheck/TcFlatten.lhs
@@ -925,6 +925,9 @@ In effect they become Givens, implemented via the side-effected substitution.
 
 Note [An alternative story for the inert substitution]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+(This entire note is just background, left here in case we ever want
+ to return the the previousl state of affairs)
+
 We used (GHC 7.8) to have this story for the inert substitution inert_eqs
 
  * 'a' is not in fvs(ty)
@@ -1012,8 +1015,8 @@ Note [eqCanRewrite]
 tv ~ ty) can be used to rewrite ct2.
 
 The EqCanRewrite Property:
-  * For any a,b in {G,W,D}  if   a canRewrite b
-                            then a canRewrite a
+  * For any a,b in {G,W,D}  if   a eqCanRewrite b
+                            then a eqCanRewrite a
   This is what guarantees that canonicalisation will terminate.
   See Note [Applying the inert substitution]
 
diff --git a/compiler/typecheck/TcSMonad.lhs b/compiler/typecheck/TcSMonad.lhs
index b756fbc..44ecc6f 100644
--- a/compiler/typecheck/TcSMonad.lhs
+++ b/compiler/typecheck/TcSMonad.lhs
@@ -328,34 +328,8 @@ The InertCans represents a collection of constraints with the following properti
     to the CTyEqCan equalities (modulo canRewrite of course;
     eg a wanted cannot rewrite a given)
 
-  * CTyEqCan equalities _do_not_ form an idempotent substitution, but
-    they are guaranteed to not have any occurs errors. Additional notes:
-
-       - The lack of idempotence of the inert substitution implies
-         that we must make sure that when we rewrite a constraint we
-         apply the substitution /recursively/ to the types
-         involved. Currently the one AND ONLY way in the whole
-         constraint solver that we rewrite types and constraints wrt
-         to the inert substitution is TcFlatten/flattenTyVar.
-
-       - In the past we did try to have the inert substitution as
-         idempotent as possible but this would only be true for
-         constraints of the same flavor, so in total the inert
-         substitution could not be idempotent, due to flavor-related
-         issued.  Note [Non-idempotent inert substitution] in TcFlatten
-         explains what is going on.
-
-       - Whenever a constraint ends up in the worklist we do
-         recursively apply exhaustively the inert substitution to it
-         to check for occurs errors.  But if an equality is already in
-         the inert set and we can guarantee that adding a new equality
-         will not cause the first equality to have an occurs check
-         then we do not rewrite the inert equality.  This happens in
-         TcInteract, rewriteInertEqsFromInertEq.
-
-         See Note [Delicate equality kick-out] to see which inert
-         equalities can safely stay in the inert set and which must be
-         kicked out to be rewritten and re-checked for occurs errors.
+  * CTyEqCan equalities: see Note [Applying the inert substitution]
+                         in TcFlatten
 
 Note [Type family equations]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~