2 Module for type coercions, as in System FC.
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4 Coercions are represented as types, and their kinds tell what types the
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7 The coercion kind constructor is a special TyCon that must always be saturated
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9 typeKind (symCoercion type) :: TyConApp CoercionTyCon{...} [type, type]
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15 mkCoKind, mkReflCoKind, splitCoercionKind_maybe, splitCoercionKind,
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16 coercionKind, coercionKinds, coercionKindPredTy,
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18 -- Equality predicates
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19 isEqPred, mkEqPred, getEqPredTys, isEqPredTy,
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21 -- Coercion transformations
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22 mkSymCoercion, mkTransCoercion,
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23 mkLeftCoercion, mkRightCoercion, mkInstCoercion, mkAppCoercion,
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24 mkForAllCoercion, mkFunCoercion, mkInstsCoercion, mkUnsafeCoercion,
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25 mkNewTypeCoercion, mkAppsCoercion,
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27 splitNewTypeRepCo_maybe, decomposeCo,
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29 unsafeCoercionTyCon, symCoercionTyCon,
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30 transCoercionTyCon, leftCoercionTyCon,
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31 rightCoercionTyCon, instCoercionTyCon -- needed by TysWiredIn
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34 #include "HsVersions.h"
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37 import Type ( Type, Kind, PredType, substTyWith, mkAppTy, mkForAllTy,
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38 mkFunTy, splitAppTy_maybe, splitForAllTy_maybe, coreView,
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39 kindView, mkTyConApp, isCoercionKind, isEqPred, mkAppTys
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41 import TyCon ( TyCon, tyConArity, mkCoercionTyCon, isNewTyCon,
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42 newTyConRhs, newTyConCo,
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43 isCoercionTyCon, isCoercionTyCon_maybe )
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44 import Var ( Var, TyVar, isTyVar, tyVarKind )
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45 import Name ( BuiltInSyntax(..), Name, mkWiredInName, tcName )
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46 import OccName ( mkOccNameFS )
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47 import PrelNames ( symCoercionTyConKey,
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48 transCoercionTyConKey, leftCoercionTyConKey,
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49 rightCoercionTyConKey, instCoercionTyConKey,
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50 unsafeCoercionTyConKey, gHC_PRIM
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52 import Util ( lengthIs, snocView )
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53 import Unique ( hasKey )
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54 import BasicTypes ( Arity )
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59 ------------------------------
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60 decomposeCo :: Arity -> Coercion -> [Coercion]
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61 -- (decomposeCo 3 c) = [right (left (left c)), right (left c), right c]
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66 go n co cos = go (n-1) (mkLeftCoercion co)
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67 (mkRightCoercion co : cos)
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69 ------------------------------
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71 -------------------------------------------------------
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72 -- and some coercion kind stuff
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74 isEqPredTy (PredTy pred) = isEqPred pred
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75 isEqPredTy other = False
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77 mkEqPred :: (Type, Type) -> PredType
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78 mkEqPred (ty1, ty2) = EqPred ty1 ty2
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80 getEqPredTys :: PredType -> (Type,Type)
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81 getEqPredTys (EqPred ty1 ty2) = (ty1, ty2)
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82 getEqPredTys other = pprPanic "getEqPredTys" (ppr other)
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84 mkCoKind :: Type -> Type -> CoercionKind
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85 mkCoKind ty1 ty2 = PredTy (EqPred ty1 ty2)
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87 mkReflCoKind :: Type -> CoercionKind
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88 mkReflCoKind ty = mkCoKind ty ty
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90 splitCoercionKind :: CoercionKind -> (Type, Type)
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91 splitCoercionKind co | Just co' <- kindView co = splitCoercionKind co'
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92 splitCoercionKind (PredTy (EqPred ty1 ty2)) = (ty1, ty2)
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94 splitCoercionKind_maybe :: Kind -> Maybe (Type, Type)
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95 splitCoercionKind_maybe co | Just co' <- kindView co = splitCoercionKind_maybe co'
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96 splitCoercionKind_maybe (PredTy (EqPred ty1 ty2)) = Just (ty1, ty2)
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97 splitCoercionKind_maybe other = Nothing
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99 isCoVar :: Var -> Bool
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100 isCoVar tv = isTyVar tv && isCoercionKind (tyVarKind tv)
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102 type Coercion = Type
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103 type CoercionKind = Kind -- A CoercionKind is always of form (ty1 :=: ty2)
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105 coercionKind :: Coercion -> (Type, Type)
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106 -- c :: (t1 :=: t2)
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107 -- Then (coercionKind c) = (t1,t2)
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109 coercionKind (TyVarTy a) | isCoVar a = splitCoercionKind (tyVarKind a)
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110 | otherwise = let t = (TyVarTy a) in (t, t)
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111 coercionKind (AppTy ty1 ty2)
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112 = let (t1, t2) = coercionKind ty1
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113 (s1, s2) = coercionKind ty2 in
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114 (mkAppTy t1 s1, mkAppTy t2 s2)
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115 coercionKind (TyConApp tc args)
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116 | Just (ar, rule) <- isCoercionTyCon_maybe tc
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117 = if length args >= ar
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118 then splitCoercionKind (rule args)
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119 else pprPanic ("arity/arguments mismatch in coercionKind:")
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120 (ppr ar $$ ppr tc <+> ppr args)
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122 = let (lArgs, rArgs) = coercionKinds args in
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123 (TyConApp tc lArgs, TyConApp tc rArgs)
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124 coercionKind (FunTy ty1 ty2)
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125 = let (t1, t2) = coercionKind ty1
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126 (s1, s2) = coercionKind ty2 in
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127 (mkFunTy t1 s1, mkFunTy t2 s2)
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128 coercionKind (ForAllTy tv ty)
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129 = let (ty1, ty2) = coercionKind ty in
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130 (ForAllTy tv ty1, ForAllTy tv ty2)
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131 coercionKind (NoteTy _ ty) = coercionKind ty
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132 coercionKind (PredTy (EqPred c1 c2))
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133 = let k1 = coercionKindPredTy c1
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134 k2 = coercionKindPredTy c2 in
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136 coercionKind (PredTy (ClassP cl args))
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137 = let (lArgs, rArgs) = coercionKinds args in
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138 (PredTy (ClassP cl lArgs), PredTy (ClassP cl rArgs))
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139 coercionKind (PredTy (IParam name ty))
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140 = let (ty1, ty2) = coercionKind ty in
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141 (PredTy (IParam name ty1), PredTy (IParam name ty2))
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143 coercionKindPredTy :: Coercion -> CoercionKind
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144 coercionKindPredTy c = let (t1, t2) = coercionKind c in mkCoKind t1 t2
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146 coercionKinds :: [Coercion] -> ([Type], [Type])
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147 coercionKinds tys = unzip $ map coercionKind tys
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149 -------------------------------------
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150 -- Coercion kind and type mk's
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151 -- (make saturated TyConApp CoercionTyCon{...} args)
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153 mkCoercion coCon args = ASSERT( tyConArity coCon == length args )
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154 TyConApp coCon args
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156 mkAppCoercion, mkFunCoercion, mkTransCoercion, mkInstCoercion :: Coercion -> Coercion -> Coercion
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157 mkSymCoercion, mkLeftCoercion, mkRightCoercion :: Coercion -> Coercion
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159 mkAppCoercion co1 co2 = mkAppTy co1 co2
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160 mkAppsCoercion co1 tys = foldl mkAppTy co1 tys
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161 -- note that a TyVar should be used here, not a CoVar (nor a TcTyVar)
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162 mkForAllCoercion tv co = ASSERT ( isTyVar tv ) mkForAllTy tv co
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163 mkFunCoercion co1 co2 = mkFunTy co1 co2
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166 | Just co2 <- splitSymCoercion_maybe co = co2
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167 | Just (co1, co2) <- splitAppCoercion_maybe co
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168 -- should make this case better
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169 = mkAppCoercion (mkSymCoercion co1) (mkSymCoercion co2)
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170 | Just (co1, co2) <- splitTransCoercion_maybe co
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171 = mkTransCoercion (mkSymCoercion co1) (mkSymCoercion co2)
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172 | Just (co, ty) <- splitInstCoercion_maybe co
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173 = mkInstCoercion (mkSymCoercion co) ty
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174 | Just co <- splitLeftCoercion_maybe co
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175 = mkLeftCoercion (mkSymCoercion co)
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176 | Just co <- splitRightCoercion_maybe co
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177 = mkRightCoercion (mkSymCoercion co)
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178 mkSymCoercion (ForAllTy tv ty) = ForAllTy tv (mkSymCoercion ty)
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179 -- for atomic types and constructors, we can just ignore sym since these
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180 -- are reflexive coercions
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181 mkSymCoercion (TyVarTy tv)
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182 | isCoVar tv = mkCoercion symCoercionTyCon [TyVarTy tv]
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183 | otherwise = TyVarTy tv
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184 mkSymCoercion co = mkCoercion symCoercionTyCon [co]
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185 -- this should not happen but does
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187 -- Smart constructors for left and right
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189 | Just (co', _) <- splitAppCoercion_maybe co = co'
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190 | otherwise = mkCoercion leftCoercionTyCon [co]
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192 mkRightCoercion co
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193 | Just (co1, co2) <- splitAppCoercion_maybe co = co2
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194 | otherwise = mkCoercion rightCoercionTyCon [co]
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196 mkTransCoercion co1 co2 = mkCoercion transCoercionTyCon [co1, co2]
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198 mkInstCoercion co ty = mkCoercion instCoercionTyCon [co, ty]
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200 mkInstsCoercion co tys = foldl mkInstCoercion co tys
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202 splitSymCoercion_maybe :: Coercion -> Maybe Coercion
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203 splitSymCoercion_maybe (TyConApp tc [co]) =
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204 if tc `hasKey` symCoercionTyConKey
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207 splitSymCoercion_maybe co = Nothing
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209 splitAppCoercion_maybe :: Coercion -> Maybe (Coercion, Coercion)
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210 -- Splits a coercion application, being careful *not* to split (left c), etc
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211 -- which are really sytactic constructs, not applications
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212 splitAppCoercion_maybe co | Just co' <- coreView co = splitAppCoercion_maybe co'
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213 splitAppCoercion_maybe (FunTy ty1 ty2) = Just (TyConApp funTyCon [ty1], ty2)
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214 splitAppCoercion_maybe (AppTy ty1 ty2) = Just (ty1, ty2)
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215 splitAppCoercion_maybe (TyConApp tc tys)
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216 | not (isCoercionTyCon tc)
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217 = case snocView tys of
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218 Just (tys', ty') -> Just (TyConApp tc tys', ty')
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220 splitAppCoercion_maybe co = Nothing
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222 splitTransCoercion_maybe :: Coercion -> Maybe (Coercion, Coercion)
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223 splitTransCoercion_maybe (TyConApp tc [ty1, ty2])
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224 = if tc `hasKey` transCoercionTyConKey then
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228 splitTransCoercion_maybe other = Nothing
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230 splitInstCoercion_maybe :: Coercion -> Maybe (Coercion, Type)
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231 splitInstCoercion_maybe (TyConApp tc [ty1, ty2])
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232 = if tc `hasKey` instCoercionTyConKey then
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236 splitInstCoercion_maybe other = Nothing
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238 splitLeftCoercion_maybe :: Coercion -> Maybe Coercion
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239 splitLeftCoercion_maybe (TyConApp tc [co])
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240 = if tc `hasKey` leftCoercionTyConKey then
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244 splitLeftCoercion_maybe other = Nothing
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246 splitRightCoercion_maybe :: Coercion -> Maybe Coercion
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247 splitRightCoercion_maybe (TyConApp tc [co])
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248 = if tc `hasKey` rightCoercionTyConKey then
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252 splitRightCoercion_maybe other = Nothing
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254 -- Unsafe coercion is not safe, it is used when we know we are dealing with
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255 -- bottom, which is the one case in which it is safe
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256 mkUnsafeCoercion :: Type -> Type -> Coercion
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257 mkUnsafeCoercion ty1 ty2
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258 = mkCoercion unsafeCoercionTyCon [ty1, ty2]
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261 -- make the coercion associated with a newtype
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262 mkNewTypeCoercion :: Name -> TyCon -> [TyVar] -> Type -> TyCon
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263 mkNewTypeCoercion name tycon tvs rhs_ty
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264 = ASSERT (length tvs == tyConArity tycon)
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265 mkCoercionTyCon name (tyConArity tycon) rule
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267 rule args = mkCoKind (substTyWith tvs args rhs_ty) (TyConApp tycon args)
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269 --------------------------------------
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270 -- Coercion Type Constructors...
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272 -- Example. The coercion ((sym c) (sym d) (sym e))
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273 -- will be represented by (TyConApp sym [c, sym d, sym e])
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274 -- If sym c :: p1=q1
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277 -- then ((sym c) (sym d) (sym e)) :: (p1 p2 p3)=(q1 q2 q3)
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279 -- (mkKindingFun f) is given the args [c, sym d, sym e]
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280 mkKindingFun :: ([Type] -> (Type, Type, [Type])) -> [Type] -> Kind
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281 mkKindingFun f args =
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282 let (ty1, ty2, rest) = f args in
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283 let (argtys1, argtys2) = unzip (map coercionKind rest) in
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284 mkCoKind (mkAppTys ty1 argtys1) (mkAppTys ty2 argtys2)
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287 symCoercionTyCon, transCoercionTyCon, leftCoercionTyCon, rightCoercionTyCon, instCoercionTyCon :: TyCon
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288 -- Each coercion TyCon is built with the special CoercionTyCon record and
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289 -- carries its won kinding rule. Such CoercionTyCons must be fully applied
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290 -- by any TyConApp in which they are applied, however they may also be over
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291 -- applied (see example above) and the kinding function must deal with this.
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292 symCoercionTyCon =
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293 mkCoercionTyCon symCoercionTyConName 1 (mkKindingFun flipCoercionKindOf)
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295 flipCoercionKindOf (co:rest) = (ty2, ty1, rest)
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297 (ty1, ty2) = coercionKind co
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299 transCoercionTyCon =
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300 mkCoercionTyCon transCoercionTyConName 2 (mkKindingFun composeCoercionKindsOf)
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302 composeCoercionKindsOf (co1:co2:rest) = (a1, r2, rest)
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304 (a1, r1) = coercionKind co1
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305 (a2, r2) = coercionKind co2
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307 leftCoercionTyCon =
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308 mkCoercionTyCon leftCoercionTyConName 1 (mkKindingFun leftProjectCoercionKindOf)
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310 leftProjectCoercionKindOf (co:rest) = (ty1, ty2, rest)
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312 (ty1,ty2) = fst (splitCoercionKindOf co)
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314 rightCoercionTyCon =
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315 mkCoercionTyCon rightCoercionTyConName 1 (mkKindingFun rightProjectCoercionKindOf)
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317 rightProjectCoercionKindOf (co:rest) = (ty1, ty2, rest)
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319 (ty1,ty2) = snd (splitCoercionKindOf co)
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321 splitCoercionKindOf :: Type -> ((Type,Type), (Type,Type))
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322 -- Helper for left and right. Finds coercion kind of its input and
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323 -- returns the left and right projections of the coercion...
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325 -- if c :: t1 s1 :=: t2 s2 then splitCoercionKindOf c = ((t1, t2), (s1, s2))
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326 splitCoercionKindOf co
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327 | Just (ty1, ty2) <- splitCoercionKind_maybe (coercionKindPredTy co)
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328 , Just (ty_fun1, ty_arg1) <- splitAppTy_maybe ty1
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329 , Just (ty_fun2, ty_arg2) <- splitAppTy_maybe ty2
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330 = ((ty_fun1, ty_fun2),(ty_arg1, ty_arg2))
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333 = mkCoercionTyCon instCoercionTyConName 2 (mkKindingFun instCoercionKind)
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335 instantiateCo t s =
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336 let Just (tv, ty) = splitForAllTy_maybe t in
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337 substTyWith [tv] [s] ty
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339 instCoercionKind (co1:ty:rest) = (instantiateCo t1 ty, instantiateCo t2 ty, rest)
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340 where (t1, t2) = coercionKind co1
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342 unsafeCoercionTyCon
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343 = mkCoercionTyCon unsafeCoercionTyConName 2 (mkKindingFun unsafeCoercionKind)
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345 unsafeCoercionKind (ty1:ty2:rest) = (ty1,ty2,rest)
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347 --------------------------------------
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348 -- ...and their names
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350 mkCoConName occ key coCon = mkWiredInName gHC_PRIM (mkOccNameFS tcName occ)
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351 key Nothing (ATyCon coCon) BuiltInSyntax
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353 transCoercionTyConName = mkCoConName FSLIT("trans") transCoercionTyConKey transCoercionTyCon
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354 symCoercionTyConName = mkCoConName FSLIT("sym") symCoercionTyConKey symCoercionTyCon
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355 leftCoercionTyConName = mkCoConName FSLIT("left") leftCoercionTyConKey leftCoercionTyCon
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356 rightCoercionTyConName = mkCoConName FSLIT("right") rightCoercionTyConKey rightCoercionTyCon
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357 instCoercionTyConName = mkCoConName FSLIT("inst") instCoercionTyConKey instCoercionTyCon
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358 unsafeCoercionTyConName = mkCoConName FSLIT("CoUnsafe") unsafeCoercionTyConKey unsafeCoercionTyCon
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362 -- this is here to avoid module loops
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363 splitNewTypeRepCo_maybe :: Type -> Maybe (Type, Coercion)
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364 -- Sometimes we want to look through a recursive newtype, and that's what happens here
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365 -- It only strips *one layer* off, so the caller will usually call itself recursively
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366 -- Only applied to types of kind *, hence the newtype is always saturated
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367 splitNewTypeRepCo_maybe ty
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368 | Just ty' <- coreView ty = splitNewTypeRepCo_maybe ty'
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369 splitNewTypeRepCo_maybe (TyConApp tc tys)
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371 = ASSERT( tys `lengthIs` tyConArity tc ) -- splitNewTypeRepCo_maybe only be applied
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372 -- to *types* (of kind *)
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373 case newTyConRhs tc of
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375 ASSERT( length tvs == length tys )
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376 Just (substTyWith tvs tys rep_ty, mkTyConApp co_con tys)
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378 co_con = maybe (pprPanic "splitNewTypeRepCo_maybe" (ppr tc)) id (newTyConCo tc)
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380 splitNewTypeRepCo_maybe other = Nothing
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