4 -- the "tc" prefix indicates that matching always
5 -- respects newtypes (rather than looking through them)
6 tcMatchTys, tcMatchTyX, ruleMatchTyX, tcMatchPreds, MatchEnv(..)
9 #include "HsVersions.h"
11 import Var ( Var, TyVar, tyVarKind )
14 import Type ( typeKind, tyVarsOfType, tyVarsOfTypes, tyVarsOfTheta,
15 TvSubstEnv, emptyTvSubstEnv, TvSubst(..), tcEqTypeX,
16 tcView, isSubKind, repSplitAppTy_maybe )
17 import TypeRep ( Type(..), PredType(..) )
23 %************************************************************************
27 %************************************************************************
30 Matching is much tricker than you might think.
32 1. The substitution we generate binds the *template type variables*
33 which are given to us explicitly.
35 2. We want to match in the presence of foralls;
36 e.g (forall a. t1) ~ (forall b. t2)
38 That is what the RnEnv2 is for; it does the alpha-renaming
39 that makes it as if a and b were the same variable.
40 Initialising the RnEnv2, so that it can generate a fresh
41 binder when necessary, entails knowing the free variables of
44 3. We must be careful not to bind a template type variable to a
45 locally bound variable. E.g.
46 (forall a. x) ~ (forall b. b)
47 where x is the template type variable. Then we do not want to
48 bind x to a/b! This is a kind of occurs check.
49 The necessary locals accumulate in the RnEnv2.
54 = ME { me_tmpls :: VarSet -- Template tyvars
55 , me_env :: RnEnv2 -- Renaming envt for nested foralls
56 } -- In-scope set includes template tyvars
58 tcMatchTys :: TyVarSet -- Template tyvars
61 -> Maybe TvSubst -- One-shot; in principle the template
62 -- variables could be free in the target
64 tcMatchTys tmpls tys1 tys2
65 = case match_tys menv emptyTvSubstEnv tys1 tys2 of
66 Just subst_env -> Just (TvSubst in_scope subst_env)
69 menv = ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope }
70 in_scope = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
71 -- We're assuming that all the interesting
72 -- tyvars in tys1 are in tmpls
74 -- This is similar, but extends a substitution
75 tcMatchTyX :: TyVarSet -- Template tyvars
76 -> TvSubst -- Substitution to extend
80 tcMatchTyX tmpls (TvSubst in_scope subst_env) ty1 ty2
81 = case match menv subst_env ty1 ty2 of
82 Just subst_env -> Just (TvSubst in_scope subst_env)
85 menv = ME {me_tmpls = tmpls, me_env = mkRnEnv2 in_scope}
88 :: [TyVar] -- Bind these
89 -> [PredType] -> [PredType]
91 tcMatchPreds tmpls ps1 ps2
92 = match_list (match_pred menv) emptyTvSubstEnv ps1 ps2
94 menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
95 in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
97 -- This one is called from the expression matcher, which already has a MatchEnv in hand
98 ruleMatchTyX :: MatchEnv
99 -> TvSubstEnv -- Substitution to extend
104 ruleMatchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
107 Now the internals of matching
110 match :: MatchEnv -- For the most part this is pushed downwards
111 -> TvSubstEnv -- Substitution so far:
112 -- Domain is subset of template tyvars
113 -- Free vars of range is subset of
114 -- in-scope set of the RnEnv2
115 -> Type -> Type -- Template and target respectively
117 -- This matcher works on source types; that is,
118 -- it respects NewTypes and PredType
120 match menv subst ty1 ty2 | Just ty1' <- tcView ty1 = match menv subst ty1' ty2
121 match menv subst ty1 ty2 | Just ty2' <- tcView ty2 = match menv subst ty1 ty2'
123 match menv subst (TyVarTy tv1) ty2
124 | tv1 `elemVarSet` me_tmpls menv
125 = case lookupVarEnv subst tv1' of
126 Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
127 -> Nothing -- Occurs check
128 | not (typeKind ty2 `isSubKind` tyVarKind tv1)
129 -> Nothing -- Kind mis-match
131 -> Just (extendVarEnv subst tv1 ty2)
133 Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
134 -- ty1 has no locally-bound variables, hence nukeRnEnvL
135 -- Note tcEqType...we are doing source-type matching here
140 | otherwise -- tv1 is not a template tyvar
142 TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
146 tv1' = rnOccL rn_env tv1
148 match menv subst (ForAllTy tv1 ty1) (ForAllTy tv2 ty2)
149 = match menv' subst ty1 ty2
150 where -- Use the magic of rnBndr2 to go under the binders
151 menv' = menv { me_env = rnBndr2 (me_env menv) tv1 tv2 }
153 match menv subst (PredTy p1) (PredTy p2)
154 = match_pred menv subst p1 p2
155 match menv subst (TyConApp tc1 tys1) (TyConApp tc2 tys2)
156 | tc1 == tc2 = match_tys menv subst tys1 tys2
157 match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
158 = do { subst' <- match menv subst ty1a ty2a
159 ; match menv subst' ty1b ty2b }
160 match menv subst (AppTy ty1a ty1b) ty2
161 | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
162 = do { subst' <- match menv subst ty1a ty2a
163 ; match menv subst' ty1b ty2b }
165 match menv subst ty1 ty2
169 match_tys menv subst tys1 tys2 = match_list (match menv) subst tys1 tys2
172 match_list :: (TvSubstEnv -> a -> a -> Maybe TvSubstEnv)
173 -> TvSubstEnv -> [a] -> [a] -> Maybe TvSubstEnv
174 match_list fn subst [] [] = Just subst
175 match_list fn subst (ty1:tys1) (ty2:tys2) = do { subst' <- fn subst ty1 ty2
176 ; match_list fn subst' tys1 tys2 }
177 match_list fn subst tys1 tys2 = Nothing
180 match_pred menv subst (ClassP c1 tys1) (ClassP c2 tys2)
181 | c1 == c2 = match_tys menv subst tys1 tys2
182 match_pred menv subst (IParam n1 t1) (IParam n2 t2)
183 | n1 == n2 = match menv subst t1 t2
184 match_pred menv subst p1 p2 = Nothing