From c271e32eac65ee95ba1aacc72ed1b24b58ef17ad Mon Sep 17 00:00:00 2001 From: Joachim Breitner Date: Sun, 26 Jan 2014 11:36:23 +0000 Subject: Add GHC.Prim.oneShot to allow the programer to explictitly set the oneShot flag. This helps with #7994 and will be used in left folds. Also see https://ghc.haskell.org/trac/ghc/wiki/OneShot This commit touches libraries/base/GHC/Event/Manager.hs (which used to have a local definition of the name oneShot) to avoid a shadowing error. Differential Revision: https://phabricator.haskell.org/D392 --- libraries/ghc-prim/GHC/Magic.hs | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) (limited to 'libraries/ghc-prim') diff --git a/libraries/ghc-prim/GHC/Magic.hs b/libraries/ghc-prim/GHC/Magic.hs index 081b838c46..1a6af9237d 100644 --- a/libraries/ghc-prim/GHC/Magic.hs +++ b/libraries/ghc-prim/GHC/Magic.hs @@ -17,7 +17,7 @@ -- ----------------------------------------------------------------------------- -module GHC.Magic ( inline, lazy ) where +module GHC.Magic ( inline, lazy, oneShot ) where -- | The call @inline f@ arranges that 'f' is inlined, regardless of -- its size. More precisely, the call @inline f@ rewrites to the @@ -64,3 +64,12 @@ lazy x = x -- sees it as lazy. Then the worker/wrapper phase inlines it. -- Result: happiness + +-- | The 'oneShot' function can be used to give a hint to the compiler that its +-- argument will be called at most once, which may (or may not) enable certain +-- optimizations. It can be useful to improve the performance of code in continuation +-- passing style. +oneShot :: (a -> b) -> (a -> b) +oneShot f = f +-- Implementation note: This is wired in in MkId.lhs, so the code here is +-- mostly there to have a place for the documentation. -- cgit v1.2.1