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Diffstat (limited to 'compiler/GHC/Core/TyCo/Rep.hs')
| -rw-r--r-- | compiler/GHC/Core/TyCo/Rep.hs | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/compiler/GHC/Core/TyCo/Rep.hs b/compiler/GHC/Core/TyCo/Rep.hs index 493b2d767a..636dc87405 100644 --- a/compiler/GHC/Core/TyCo/Rep.hs +++ b/compiler/GHC/Core/TyCo/Rep.hs @@ -1928,13 +1928,16 @@ GHC.Core.Multiplicity above this module. -} -- | A shorthand for data with an attached 'Mult' element (the multiplicity). -data Scaled a = Scaled Mult a +data Scaled a = Scaled !Mult a deriving (Data.Data) -- You might think that this would be a natural candidate for -- Functor, Traversable but Krzysztof says (!3674) "it was too easy -- to accidentally lift functions (substitutions, zonking etc.) from -- Type -> Type to Scaled Type -> Scaled Type, ignoring -- multiplicities and causing bugs". So we don't. + -- + -- Being strict in a is worse for performance, so we are only strict on the + -- Mult part of scaled. instance (Outputable a) => Outputable (Scaled a) where |