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, mkTyVarTys,
15 TvSubstEnv, emptyTvSubstEnv, TvSubst(..), substTy, tcEqTypeX,
16 mkOpenTvSubst, tcView, isSubKind, eqKind, repSplitAppTy_maybe )
17 import TypeRep ( Type(..), PredType(..), funTyCon )
18 import DataCon ( DataCon, dataConResTys )
19 import Util ( snocView )
20 import ErrUtils ( Message )
26 %************************************************************************
30 %************************************************************************
33 Matching is much tricker than you might think.
35 1. The substitution we generate binds the *template type variables*
36 which are given to us explicitly.
38 2. We want to match in the presence of foralls;
39 e.g (forall a. t1) ~ (forall b. t2)
41 That is what the RnEnv2 is for; it does the alpha-renaming
42 that makes it as if a and b were the same variable.
43 Initialising the RnEnv2, so that it can generate a fresh
44 binder when necessary, entails knowing the free variables of
47 3. We must be careful not to bind a template type variable to a
48 locally bound variable. E.g.
49 (forall a. x) ~ (forall b. b)
50 where x is the template type variable. Then we do not want to
51 bind x to a/b! This is a kind of occurs check.
52 The necessary locals accumulate in the RnEnv2.
57 = ME { me_tmpls :: VarSet -- Template tyvars
58 , me_env :: RnEnv2 -- Renaming envt for nested foralls
59 } -- In-scope set includes template tyvars
61 tcMatchTys :: TyVarSet -- Template tyvars
64 -> Maybe TvSubst -- One-shot; in principle the template
65 -- variables could be free in the target
67 tcMatchTys tmpls tys1 tys2
68 = case match_tys menv emptyTvSubstEnv tys1 tys2 of
69 Just subst_env -> Just (TvSubst in_scope subst_env)
72 menv = ME { me_tmpls = tmpls, me_env = mkRnEnv2 in_scope }
73 in_scope = mkInScopeSet (tmpls `unionVarSet` tyVarsOfTypes tys2)
74 -- We're assuming that all the interesting
75 -- tyvars in tys1 are in tmpls
77 -- This is similar, but extends a substitution
78 tcMatchTyX :: TyVarSet -- Template tyvars
79 -> TvSubst -- Substitution to extend
83 tcMatchTyX tmpls (TvSubst in_scope subst_env) ty1 ty2
84 = case match menv subst_env ty1 ty2 of
85 Just subst_env -> Just (TvSubst in_scope subst_env)
88 menv = ME {me_tmpls = tmpls, me_env = mkRnEnv2 in_scope}
91 :: [TyVar] -- Bind these
92 -> [PredType] -> [PredType]
94 tcMatchPreds tmpls ps1 ps2
95 = match_list (match_pred menv) emptyTvSubstEnv ps1 ps2
97 menv = ME { me_tmpls = mkVarSet tmpls, me_env = mkRnEnv2 in_scope_tyvars }
98 in_scope_tyvars = mkInScopeSet (tyVarsOfTheta ps1 `unionVarSet` tyVarsOfTheta ps2)
100 -- This one is called from the expression matcher, which already has a MatchEnv in hand
101 ruleMatchTyX :: MatchEnv
102 -> TvSubstEnv -- Substitution to extend
107 ruleMatchTyX menv subst ty1 ty2 = match menv subst ty1 ty2 -- Rename for export
110 Now the internals of matching
113 match :: MatchEnv -- For the most part this is pushed downwards
114 -> TvSubstEnv -- Substitution so far:
115 -- Domain is subset of template tyvars
116 -- Free vars of range is subset of
117 -- in-scope set of the RnEnv2
118 -> Type -> Type -- Template and target respectively
120 -- This matcher works on source types; that is,
121 -- it respects NewTypes and PredType
123 match menv subst ty1 ty2 | Just ty1' <- tcView ty1 = match menv subst ty1' ty2
124 match menv subst ty1 ty2 | Just ty2' <- tcView ty2 = match menv subst ty1 ty2'
126 match menv subst (TyVarTy tv1) ty2
127 | tv1 `elemVarSet` me_tmpls menv
128 = case lookupVarEnv subst tv1' of
129 Nothing | any (inRnEnvR rn_env) (varSetElems (tyVarsOfType ty2))
130 -> Nothing -- Occurs check
131 | not (typeKind ty2 `isSubKind` tyVarKind tv1)
132 -> Nothing -- Kind mis-match
134 -> Just (extendVarEnv subst tv1 ty2)
136 Just ty1' | tcEqTypeX (nukeRnEnvL rn_env) ty1' ty2
137 -- ty1 has no locally-bound variables, hence nukeRnEnvL
138 -- Note tcEqType...we are doing source-type matching here
143 | otherwise -- tv1 is not a template tyvar
145 TyVarTy tv2 | tv1' == rnOccR rn_env tv2 -> Just subst
149 tv1' = rnOccL rn_env tv1
151 match menv subst (ForAllTy tv1 ty1) (ForAllTy tv2 ty2)
152 = match menv' subst ty1 ty2
153 where -- Use the magic of rnBndr2 to go under the binders
154 menv' = menv { me_env = rnBndr2 (me_env menv) tv1 tv2 }
156 match menv subst (PredTy p1) (PredTy p2)
157 = match_pred menv subst p1 p2
158 match menv subst (TyConApp tc1 tys1) (TyConApp tc2 tys2)
159 | tc1 == tc2 = match_tys menv subst tys1 tys2
160 match menv subst (FunTy ty1a ty1b) (FunTy ty2a ty2b)
161 = do { subst' <- match menv subst ty1a ty2a
162 ; match menv subst' ty1b ty2b }
163 match menv subst (AppTy ty1a ty1b) ty2
164 | Just (ty2a, ty2b) <- repSplitAppTy_maybe ty2
165 = do { subst' <- match menv subst ty1a ty2a
166 ; match menv subst' ty1b ty2b }
168 match menv subst ty1 ty2
172 match_tys menv subst tys1 tys2 = match_list (match menv) subst tys1 tys2
175 match_list :: (TvSubstEnv -> a -> a -> Maybe TvSubstEnv)
176 -> TvSubstEnv -> [a] -> [a] -> Maybe TvSubstEnv
177 match_list fn subst [] [] = Just subst
178 match_list fn subst (ty1:tys1) (ty2:tys2) = do { subst' <- fn subst ty1 ty2
179 ; match_list fn subst' tys1 tys2 }
180 match_list fn subst tys1 tys2 = Nothing
183 match_pred menv subst (ClassP c1 tys1) (ClassP c2 tys2)
184 | c1 == c2 = match_tys menv subst tys1 tys2
185 match_pred menv subst (IParam n1 t1) (IParam n2 t2)
186 | n1 == n2 = match menv subst t1 t2
187 match_pred menv subst p1 p2 = Nothing