2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[TcRules]{Typechecking transformation rules}
7 module TcRules ( tcRules ) where
9 #include "HsVersions.h"
11 import HsSyn ( RuleDecl(..), RuleBndr(..), HsExpr(..), collectRuleBndrSigTys )
12 import CoreSyn ( CoreRule(..) )
13 import RnHsSyn ( RenamedRuleDecl )
14 import TcHsSyn ( TypecheckedRuleDecl, TcExpr, mkHsLet )
16 import TcSimplify ( tcSimplifyToDicts, tcSimplifyInferCheck )
17 import TcMType ( newTyVarTy )
18 import TcType ( TcTyVarSet, tyVarsOfTypes, openTypeKind )
19 import TcIfaceSig ( tcCoreExpr, tcCoreLamBndrs, tcVar )
20 import TcMonoType ( tcHsSigType, UserTypeCtxt(..), tcAddScopedTyVars )
21 import TcExpr ( tcMonoExpr )
22 import TcEnv ( tcExtendLocalValEnv )
23 import Inst ( instToId )
24 import Id ( idType, mkLocalId )
30 tcRules :: [RenamedRuleDecl] -> TcM [TypecheckedRuleDecl]
31 tcRules decls = mappM tcRule decls
33 tcRule :: RenamedRuleDecl -> TcM TypecheckedRuleDecl
34 tcRule (IfaceRule name act vars fun args rhs src_loc)
36 addErrCtxt (ruleCtxt name) $
37 tcVar fun `thenM` \ fun' ->
38 tcCoreLamBndrs vars $ \ vars' ->
39 mappM tcCoreExpr args `thenM` \ args' ->
40 tcCoreExpr rhs `thenM` \ rhs' ->
41 returnM (IfaceRuleOut fun' (Rule name act vars' args' rhs'))
43 tcRule (IfaceRuleOut fun rule) -- Built-in rules come this way
44 = tcVar fun `thenM` \ fun' ->
45 returnM (IfaceRuleOut fun' rule)
47 tcRule (HsRule name act vars lhs rhs src_loc)
49 addErrCtxt (ruleCtxt name) $
50 newTyVarTy openTypeKind `thenM` \ rule_ty ->
52 -- Deal with the tyvars mentioned in signatures
53 tcAddScopedTyVars (collectRuleBndrSigTys vars) (
55 -- Ditto forall'd variables
56 mappM new_id vars `thenM` \ ids ->
57 tcExtendLocalValEnv ids $
60 getLIE (tcMonoExpr lhs rule_ty) `thenM` \ (lhs', lhs_lie) ->
61 getLIE (tcMonoExpr rhs rule_ty) `thenM` \ (rhs', rhs_lie) ->
63 returnM (ids, lhs', rhs', lhs_lie, rhs_lie)
64 ) `thenM` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
66 -- Check that LHS has no overloading at all
67 getLIE (tcSimplifyToDicts lhs_lie) `thenM` \ (lhs_binds, lhs_dicts) ->
69 -- Gather the template variables and tyvars
71 tpl_ids = map instToId lhs_dicts ++ ids
73 -- IMPORTANT! We *quantify* over any dicts that appear in the LHS
75 -- a) The particular dictionary isn't important, because its value
76 -- depends only on the type
77 -- e.g gcd Int $fIntegralInt
78 -- Here we'd like to match against (gcd Int any_d) for any 'any_d'
80 -- b) We'd like to make available the dictionaries bound
81 -- on the LHS in the RHS, so quantifying over them is good
82 -- See the 'lhs_dicts' in tcSimplifyAndCheck for the RHS
84 -- We initially quantify over any tyvars free in *either* the rule
85 -- *or* the bound variables. The latter is important. Consider
86 -- ss (x,(y,z)) = (x,z)
87 -- RULE: forall v. fst (ss v) = fst v
88 -- The type of the rhs of the rule is just a, but v::(a,(b,c))
90 -- We also need to get the free tyvars of the LHS; see notes
91 -- below with ruleLhsTvs.
93 forall_tvs = tyVarsOfTypes (rule_ty : map idType tpl_ids)
97 -- RHS can be a bit more lenient. In particular,
98 -- we let constant dictionaries etc float outwards
100 -- NB: tcSimplifyInferCheck zonks the forall_tvs, and
101 -- knocks out any that are constrained by the environment
102 tcSimplifyInferCheck (text "tcRule")
104 lhs_dicts rhs_lie `thenM` \ (forall_tvs1, rhs_binds) ->
106 returnM (HsRule name act
107 (map RuleBndr (forall_tvs1 ++ tpl_ids)) -- yuk
108 (mkHsLet lhs_binds lhs')
109 (mkHsLet rhs_binds rhs')
112 new_id (RuleBndr var) = newTyVarTy openTypeKind `thenM` \ ty ->
113 returnM (mkLocalId var ty)
114 new_id (RuleBndrSig var rn_ty) = tcHsSigType (RuleSigCtxt var) rn_ty `thenM` \ ty ->
115 returnM (mkLocalId var ty)
117 ruleLhsTvs :: TcExpr -> TcTyVarSet
118 -- We need to gather the type variables mentioned on the LHS so we can
119 -- quantify over them. Example:
125 -- {-# RULES "myrule" foo C = 1 #-}
127 -- After type checking the LHS becomes (foo a (C a))
128 -- and we do not want to zap the unbound tyvar 'a' to (), because
129 -- that limits the applicability of the rule. Instead, we
130 -- want to quantify over it!
132 -- Fortunately the form of the LHS is pretty limited (see RnSource.validRuleLhs)
133 -- so we don't need to deal with the whole of HsSyn.
135 ruleLhsTvs (OpApp e1 op _ e2)
136 = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs op `unionVarSet` ruleLhsTvs e2
137 ruleLhsTvs (HsApp e1 e2)
138 = ruleLhsTvs e1 `unionVarSet` ruleLhsTvs e2
139 ruleLhsTvs (HsVar v) = emptyVarSet -- I don't think we need the tyvars of the Id
140 ruleLhsTvs (TyApp e1 tys)
141 = ruleLhsTvs e1 `unionVarSet` tyVarsOfTypes tys
142 ruleLhsTvs e = pprPanic "ruleLhsTvs" (ppr e)
145 ruleCtxt name = ptext SLIT("When checking the transformation rule") <+>
146 doubleQuotes (ftext name)