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Diffstat (limited to 'compiler/GHC/Core/TyCon.hs')
| -rw-r--r-- | compiler/GHC/Core/TyCon.hs | 81 |
1 files changed, 0 insertions, 81 deletions
diff --git a/compiler/GHC/Core/TyCon.hs b/compiler/GHC/Core/TyCon.hs index fc6aaf7d7b..919407376e 100644 --- a/compiler/GHC/Core/TyCon.hs +++ b/compiler/GHC/Core/TyCon.hs @@ -126,10 +126,6 @@ module GHC.Core.TyCon( primRepsCompatible, primRepCompatible, - -- * Recursion breaking - RecTcChecker, initRecTc, defaultRecTcMaxBound, - setRecTcMaxBound, checkRecTc - ) where #include "HsVersions.h" @@ -2710,83 +2706,6 @@ instance Binary Injectivity where _ -> do { xs <- get bh ; return (Injective xs) } } -{- -************************************************************************ -* * - Walking over recursive TyCons -* * -************************************************************************ - -Note [Expanding newtypes and products] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -When expanding a type to expose a data-type constructor, we need to be -careful about newtypes, lest we fall into an infinite loop. Here are -the key examples: - - newtype Id x = MkId x - newtype Fix f = MkFix (f (Fix f)) - newtype T = MkT (T -> T) - - Type Expansion - -------------------------- - T T -> T - Fix Maybe Maybe (Fix Maybe) - Id (Id Int) Int - Fix Id NO NO NO - -Notice that - * We can expand T, even though it's recursive. - * We can expand Id (Id Int), even though the Id shows up - twice at the outer level, because Id is non-recursive - -So, when expanding, we keep track of when we've seen a recursive -newtype at outermost level; and bail out if we see it again. - -We sometimes want to do the same for product types, so that the -strictness analyser doesn't unbox infinitely deeply. - -More precisely, we keep a *count* of how many times we've seen it. -This is to account for - data instance T (a,b) = MkT (T a) (T b) -Then (#10482) if we have a type like - T (Int,(Int,(Int,(Int,Int)))) -we can still unbox deeply enough during strictness analysis. -We have to treat T as potentially recursive, but it's still -good to be able to unwrap multiple layers. - -The function that manages all this is checkRecTc. --} - -data RecTcChecker = RC !Int (NameEnv Int) - -- The upper bound, and the number of times - -- we have encountered each TyCon - --- | Initialise a 'RecTcChecker' with 'defaultRecTcMaxBound'. -initRecTc :: RecTcChecker -initRecTc = RC defaultRecTcMaxBound emptyNameEnv - --- | The default upper bound (100) for the number of times a 'RecTcChecker' is --- allowed to encounter each 'TyCon'. -defaultRecTcMaxBound :: Int -defaultRecTcMaxBound = 100 --- Should we have a flag for this? - --- | Change the upper bound for the number of times a 'RecTcChecker' is allowed --- to encounter each 'TyCon'. -setRecTcMaxBound :: Int -> RecTcChecker -> RecTcChecker -setRecTcMaxBound new_bound (RC _old_bound rec_nts) = RC new_bound rec_nts - -checkRecTc :: RecTcChecker -> TyCon -> Maybe RecTcChecker --- Nothing => Recursion detected --- Just rec_tcs => Keep going -checkRecTc (RC bound rec_nts) tc - = case lookupNameEnv rec_nts tc_name of - Just n | n >= bound -> Nothing - | otherwise -> Just (RC bound (extendNameEnv rec_nts tc_name (n+1))) - Nothing -> Just (RC bound (extendNameEnv rec_nts tc_name 1)) - where - tc_name = tyConName tc - -- | Returns whether or not this 'TyCon' is definite, or a hole -- that may be filled in at some later point. See Note [Skolem abstract data] tyConSkolem :: TyCon -> Bool |