RE: [commit: ghc] master: Add rule mapFB c (λx.x) = c (2fa4421)

[Joachim Breitner]

Hi,

I guess you are right. I should also be more careful about distinguishing Phab DR that I create to get feedback from CI and review, even before I do such non-functional polishing of the patch, and ready-to-apply changes (which I'd commit myself anyways).

Joachim 




Am 8. März 2017 13:22:55 MEZ schrieb Simon Peyton Jones <simonpj at microsoft.com>:
>Joachim
>
>Please, I beg you, add a comment to explain why this rule is useful.
>I'm sure you had a good reason for adding it, but it's not apparent
>from the code.
>
>Thanks
>
>Simon
>
>|  -----Original Message-----
>|  From: ghc-commits [mailto:ghc-commits-bounces at haskell.org] On Behalf
>|  Of git at git.haskell.org
>|  Sent: 06 March 2017 23:52
>|  To: ghc-commits at haskell.org
>|  Subject: [commit: ghc] master: Add rule mapFB c (λx.x) = c (2fa4421)
>|  
>|  Repository : ssh://git@git.haskell.org/ghc
>|  
>|  On branch  : master
>|  Link       :
>| 
>https://na01.safelinks.protection.outlook.com/?url=http%3A%2F%2Fghc.ha
>| 
>skell.org%2Ftrac%2Fghc%2Fchangeset%2F2fa44217c1d9722227297eefb0d6c6aed
>| 
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>|  erved=0
>|  
>|  >---------------------------------------------------------------
>|  
>|  commit 2fa44217c1d9722227297eefb0d6c6aed7e128ca
>|  Author: Joachim Breitner <mail at joachim-breitner.de>
>|  Date:   Mon Mar 6 17:30:52 2017 -0500
>|  
>|      Add rule mapFB c (λx.x) = c
>|  
>|      Test Plan: exended T2110 with a case for that.
>|  
>|      Reviewers: austin, hvr, dfeuer, bgamari
>|  
>|      Reviewed By: dfeuer
>|  
>|      Subscribers: dfeuer, thomie
>|  
>|      Differential Revision: https://phabricator.haskell.org/D3275
>|  
>|  
>|  >---------------------------------------------------------------
>|  
>|  2fa44217c1d9722227297eefb0d6c6aed7e128ca
>|   libraries/base/GHC/Base.hs                        | 1 +
>|   testsuite/tests/simplCore/should_run/T2110.hs     | 3 +++
>|   testsuite/tests/simplCore/should_run/T2110.stdout | 1 +
>|   3 files changed, 5 insertions(+)
>|  
>|  diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs
>|  index 2f155c6..6f9d454 100644
>|  --- a/libraries/base/GHC/Base.hs
>|  +++ b/libraries/base/GHC/Base.hs
>|  @@ -973,6 +973,7 @@ mapFB c f = \x ys -> c (f x) ys
>|   "map"       [~1] forall f xs.   map f xs                = build (\c
>n
>|  -> foldr (mapFB c f) n xs)
>|   "mapList"   [1]  forall f.      foldr (mapFB (:) f) []  = map f
>|   "mapFB"     forall c f g.       mapFB (mapFB c f) g     = mapFB c
>|  (f.g)
>|  +"mapFB/id"  forall c.           mapFB c (\x -> x)       = c
>|     #-}
>|  
>|   -- See Breitner, Eisenberg, Peyton Jones, and Weirich, "Safe Zero-
>|  cost diff --git a/testsuite/tests/simplCore/should_run/T2110.hs
>|  b/testsuite/tests/simplCore/should_run/T2110.hs
>|  index 610be09..d945fac 100644
>|  --- a/testsuite/tests/simplCore/should_run/T2110.hs
>|  +++ b/testsuite/tests/simplCore/should_run/T2110.hs
>|  @@ -5,6 +5,8 @@ import Unsafe.Coerce
>|  
>|   newtype Age = Age Int
>|  
>|  +foo :: [Int] -> [Int]
>|  +foo = map id
>|   fooAge :: [Int] -> [Age]
>|   fooAge = map Age
>|   fooCoerce :: [Int] -> [Age]
>|  @@ -19,6 +21,7 @@ same x y = case reallyUnsafePtrEquality#
>|  (unsafeCoerce x) y of
>|  
>|   main = do
>|       let l = [1,2,3]
>|  +    same (foo l) l
>|       same (fooAge l) l
>|       same (fooCoerce l) l
>|       same (fooUnsafeCoerce l) l
>|  diff --git a/testsuite/tests/simplCore/should_run/T2110.stdout
>|  b/testsuite/tests/simplCore/should_run/T2110.stdout
>|  index 55f7ebb..4ff957b 100644
>|  --- a/testsuite/tests/simplCore/should_run/T2110.stdout
>|  +++ b/testsuite/tests/simplCore/should_run/T2110.stdout
>|  @@ -1,3 +1,4 @@
>|   yes
>|   yes
>|   yes
>|  +yes
>|  
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