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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2018-01-02 17:11:55 +0000 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2018-01-03 11:26:20 +0000 |
| commit | 3bf910d0ff7f82b4c316dcc08c143dbb65362366 (patch) | |
| tree | 526dd7cbf8798a083aede852d85dc3ce9637f3d6 | |
| parent | 1e12783b658043dfa836ad6003da0e283faa7716 (diff) | |
| download | haskell-3bf910d0ff7f82b4c316dcc08c143dbb65362366.tar.gz | |
Small refactoring in Coercion
* Kill unused mkHomoPhantomCo
* Refactor downgradeRole_maybe to be more perspicuous
* Don't export toPhantomCo (not used externally)
| -rw-r--r-- | compiler/types/Coercion.hs | 29 |
1 files changed, 13 insertions, 16 deletions
diff --git a/compiler/types/Coercion.hs b/compiler/types/Coercion.hs index 2a94755424..3f83b09f67 100644 --- a/compiler/types/Coercion.hs +++ b/compiler/types/Coercion.hs @@ -32,7 +32,7 @@ module Coercion ( mkNthCo, mkNthCoRole, mkLRCo, mkInstCo, mkAppCo, mkAppCos, mkTyConAppCo, mkFunCo, mkFunCos, mkForAllCo, mkForAllCos, mkHomoForAllCos, mkHomoForAllCos_NoRefl, - mkPhantomCo, mkHomoPhantomCo, toPhantomCo, + mkPhantomCo, mkUnsafeCo, mkHoleCo, mkUnivCo, mkSubCo, mkAxiomInstCo, mkProofIrrelCo, downgradeRole, maybeSubCo, mkAxiomRuleCo, @@ -909,8 +909,9 @@ mkKindCo co | otherwise = KindCo co --- input coercion is Nominal; see also Note [Role twiddling functions] mkSubCo :: Coercion -> Coercion +-- Input coercion is Nominal, result is Representational +-- see also Note [Role twiddling functions] mkSubCo (Refl Nominal ty) = Refl Representational ty mkSubCo (TyConAppCo Nominal tc cos) = TyConAppCo Representational tc (applyRoles tc cos) @@ -927,12 +928,16 @@ downgradeRole_maybe :: Role -- ^ desired role -> Coercion -> Maybe Coercion -- In (downgradeRole_maybe dr cr co) it's a precondition that -- cr = coercionRole co -downgradeRole_maybe Representational Nominal co = Just (mkSubCo co) -downgradeRole_maybe Nominal Representational _ = Nothing -downgradeRole_maybe Phantom Phantom co = Just co -downgradeRole_maybe Phantom _ co = Just (toPhantomCo co) -downgradeRole_maybe _ Phantom _ = Nothing -downgradeRole_maybe _ _ co = Just co + +downgradeRole_maybe Nominal Nominal co = Just co +downgradeRole_maybe Nominal _ _ = Nothing + +downgradeRole_maybe Representational Nominal co = Just (mkSubCo co) +downgradeRole_maybe Representational Representational co = Just co +downgradeRole_maybe Representational Phantom _ = Nothing + +downgradeRole_maybe Phantom Phantom co = Just co +downgradeRole_maybe Phantom _ co = Just (toPhantomCo co) -- | Like 'downgradeRole_maybe', but panics if the change isn't a downgrade. -- See Note [Role twiddling functions] @@ -1019,14 +1024,6 @@ mkPhantomCo :: Coercion -> Type -> Type -> Coercion mkPhantomCo h t1 t2 = mkUnivCo (PhantomProv h) Phantom t1 t2 --- | Make a phantom coercion between two types of the same kind. -mkHomoPhantomCo :: Type -> Type -> Coercion -mkHomoPhantomCo t1 t2 - = ASSERT( k1 `eqType` typeKind t2 ) - mkPhantomCo (mkNomReflCo k1) t1 t2 - where - k1 = typeKind t1 - -- takes any coercion and turns it into a Phantom coercion toPhantomCo :: Coercion -> Coercion toPhantomCo co |