| +-- The "mapFB" rule optimises compositions of map and
| +-- the "mapFB/id" rule get rids of 'map id' calls.
| +-- (Any similarity to the Functor laws for [] is expected.)
Yes, obviously. But did you have a use-case, or did you just to this on principle? If you don't have this rule what goes wrong. You must have had a proximate reason for adding it.
Oh. And I've just realised that
mapFB c id
will turn into
\x y. c x y
as soon as you inline mapFB. So why do you need a RULE to do that? Why not leave it for the inliner?
Simon
| -----Original Message-----
| From: ghc-commits [mailto:ghc-commits-bounces@haskell.org] On Behalf
| Of git@git.haskell.org
| Sent: 09 March 2017 15:14
| To: ghc-commits@haskell.org
| Subject: [commit: ghc] master: Add a comment to the mapFB rules
| (665cefe)
|
| 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%2F665cefe80d112ed2e4fb9617d277a1466
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|
| >---------------------------------------------------------------
|
| commit 665cefe80d112ed2e4fb9617d277a1466e83f9bd
| Author: Joachim Breitner
| Date: Thu Mar 9 16:13:08 2017 +0100
|
| Add a comment to the mapFB rules
|
| to amend 2fa44217c1d9722227297eefb0d6c6aed7e128ca.
|
|
| >---------------------------------------------------------------
|
| 665cefe80d112ed2e4fb9617d277a1466e83f9bd
| libraries/base/GHC/Base.hs | 6 ++++--
| 1 file changed, 4 insertions(+), 2 deletions(-)
|
| diff --git a/libraries/base/GHC/Base.hs b/libraries/base/GHC/Base.hs
| index 6f9d454..a678c22 100644
| --- a/libraries/base/GHC/Base.hs
| +++ b/libraries/base/GHC/Base.hs
| @@ -964,10 +964,12 @@ mapFB c f = \x ys -> c (f x) ys
| -- (along with build's unfolding) else we'd get an infinite loop
| -- in the rules. Hence the activation control below.
| --
| --- The "mapFB" rule optimises compositions of map.
| ---
| -- This same pattern is followed by many other functions:
| -- e.g. append, filter, iterate, repeat, etc.
| +--
| +-- The "mapFB" rule optimises compositions of map and
| +-- the "mapFB/id" rule get rids of 'map id' calls.
| +-- (Any similarity to the Functor laws for [] is expected.)
|
| {-# RULES
| "map" [~1] forall f xs. map f xs = build (\c n
| -> foldr (mapFB c f) n xs)
|
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