2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[TcRules]{Typechecking transformation rules}
7 module TcRules ( tcIfaceRules, tcSourceRules ) where
9 #include "HsVersions.h"
11 import HsSyn ( RuleDecl(..), RuleBndr(..) )
12 import CoreSyn ( CoreRule(..) )
13 import RnHsSyn ( RenamedRuleDecl )
14 import HscTypes ( PackageRuleBase )
15 import TcHsSyn ( TypecheckedRuleDecl, mkHsLet )
17 import TcSimplify ( tcSimplifyToDicts, tcSimplifyInferCheck )
18 import TcMType ( newTyVarTy )
19 import TcType ( tyVarsOfTypes, openTypeKind )
20 import TcIfaceSig ( tcCoreExpr, tcCoreLamBndrs, tcVar )
21 import TcMonoType ( kcHsSigTypes, tcHsSigType, tcScopedTyVars )
22 import TcExpr ( tcExpr )
23 import TcEnv ( tcExtendLocalValEnv, isLocalThing )
24 import Rules ( extendRuleBase )
25 import Inst ( LIE, plusLIEs, instToId )
26 import Id ( idName, idType, mkLocalId )
27 import Module ( Module )
28 import List ( partition )
33 tcIfaceRules :: PackageRuleBase -> Module -> [RenamedRuleDecl]
34 -> TcM (PackageRuleBase, [TypecheckedRuleDecl])
35 tcIfaceRules pkg_rule_base mod decls
36 = mapTc tcIfaceRule decls `thenTc` \ new_rules ->
38 (local_rules, imported_rules) = partition is_local new_rules
39 new_rule_base = foldl add pkg_rule_base imported_rules
41 returnTc (new_rule_base, local_rules)
43 add rule_base (IfaceRuleOut id rule) = extendRuleBase rule_base (id, rule)
45 -- When relinking this module from its interface-file decls
46 -- we'll have IfaceRules that are in fact local to this module
47 is_local (IfaceRuleOut n _) = isLocalThing mod n
50 tcIfaceRule :: RenamedRuleDecl -> TcM TypecheckedRuleDecl
51 -- No zonking necessary!
52 tcIfaceRule rule@(IfaceRule name vars fun args rhs src_loc)
53 = tcAddSrcLoc src_loc $
54 tcAddErrCtxt (ruleCtxt name) $
55 tcVar fun `thenTc` \ fun' ->
56 tcCoreLamBndrs vars $ \ vars' ->
57 mapTc tcCoreExpr args `thenTc` \ args' ->
58 tcCoreExpr rhs `thenTc` \ rhs' ->
60 new_rule :: TypecheckedRuleDecl
61 new_rule = IfaceRuleOut fun' (Rule name vars' args' rhs')
65 tcSourceRules :: [RenamedRuleDecl] -> TcM (LIE, [TypecheckedRuleDecl])
67 = mapAndUnzipTc tcSourceRule decls `thenTc` \ (lies, decls') ->
68 returnTc (plusLIEs lies, decls')
70 tcSourceRule (HsRule name sig_tvs vars lhs rhs src_loc)
71 = tcAddSrcLoc src_loc $
72 tcAddErrCtxt (ruleCtxt name) $
73 newTyVarTy openTypeKind `thenNF_Tc` \ rule_ty ->
75 -- Deal with the tyvars mentioned in signatures
76 tcScopedTyVars sig_tvs (kcHsSigTypes sig_tys) (
78 -- Ditto forall'd variables
79 mapNF_Tc new_id vars `thenNF_Tc` \ ids ->
80 tcExtendLocalValEnv [(idName id, id) | id <- ids] $
83 tcExpr lhs rule_ty `thenTc` \ (lhs', lhs_lie) ->
84 tcExpr rhs rule_ty `thenTc` \ (rhs', rhs_lie) ->
86 returnTc (ids, lhs', rhs', lhs_lie, rhs_lie)
87 ) `thenTc` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
89 -- Check that LHS has no overloading at all
90 tcSimplifyToDicts lhs_lie `thenTc` \ (lhs_dicts, lhs_binds) ->
92 -- Gather the template variables and tyvars
94 tpl_ids = map instToId lhs_dicts ++ ids
96 -- IMPORTANT! We *quantify* over any dicts that appear in the LHS
98 -- a) The particular dictionary isn't important, because its value
99 -- depends only on the type
100 -- e.g gcd Int $fIntegralInt
101 -- Here we'd like to match against (gcd Int any_d) for any 'any_d'
103 -- b) We'd like to make available the dictionaries bound
104 -- on the LHS in the RHS, so quantifying over them is good
105 -- See the 'lhs_dicts' in tcSimplifyAndCheck for the RHS
107 -- We initially quantify over any tyvars free in *either* the rule
108 -- *or* the bound variables. The latter is important. Consider
109 -- ss (x,(y,z)) = (x,z)
110 -- RULE: forall v. fst (ss v) = fst v
111 -- The type of the rhs of the rule is just a, but v::(a,(b,c))
113 -- It's still conceivable that there may be type variables mentioned
114 -- in the LHS, but not in the type of the lhs, nor in the binders.
115 -- They'll get zapped to (), but that's over-constraining really.
116 -- Let's see if we get a problem.
117 forall_tvs = tyVarsOfTypes (rule_ty : map idType tpl_ids)
120 -- RHS can be a bit more lenient. In particular,
121 -- we let constant dictionaries etc float outwards
124 tcSimplifyInferCheck (text "tcRule")
126 lhs_dicts rhs_lie `thenTc` \ (forall_tvs1, lie', rhs_binds) ->
128 returnTc (lie', HsRule name forall_tvs1
129 (map RuleBndr tpl_ids) -- yuk
130 (mkHsLet lhs_binds lhs')
131 (mkHsLet rhs_binds rhs')
134 sig_tys = [t | RuleBndrSig _ t <- vars]
136 new_id (RuleBndr var) = newTyVarTy openTypeKind `thenNF_Tc` \ ty ->
137 returnNF_Tc (mkLocalId var ty)
138 new_id (RuleBndrSig var rn_ty) = tcHsSigType rn_ty `thenTc` \ ty ->
139 returnNF_Tc (mkLocalId var ty)
141 ruleCtxt name = ptext SLIT("When checking the transformation rule") <+>
142 doubleQuotes (ptext name)