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 ( HsDecl(..), RuleDecl(..), RuleBndr(..), HsTyVarBndr(..) )
12 import CoreSyn ( CoreRule(..) )
13 import RnHsSyn ( RenamedHsDecl )
14 import TcHsSyn ( TypecheckedRuleDecl, mkHsLet )
16 import TcSimplify ( tcSimplifyToDicts, tcSimplifyAndCheck )
17 import TcType ( zonkTcTypes, newTyVarTy_OpenKind )
18 import TcIfaceSig ( tcCoreExpr, tcCoreLamBndrs, tcVar )
19 import TcMonoType ( tcHsSigType, tcHsTyVar, checkSigTyVars )
20 import TcExpr ( tcExpr )
21 import TcEnv ( tcExtendLocalValEnv, newLocalId,
24 import Inst ( LIE, emptyLIE, plusLIEs, instToId )
25 import Id ( idType, idName, mkVanillaId )
27 import Type ( tyVarsOfTypes )
28 import Bag ( bagToList )
34 tcRules :: [RenamedHsDecl] -> TcM s (LIE, [TypecheckedRuleDecl])
35 tcRules decls = mapAndUnzipTc tcRule [rule | RuleD rule <- decls] `thenTc` \ (lies, rules) ->
36 returnTc (plusLIEs lies, rules)
38 tcRule (IfaceRule name vars fun args rhs src_loc)
39 = tcAddSrcLoc src_loc $
40 tcAddErrCtxt (ruleCtxt name) $
41 tcVar fun `thenTc` \ fun' ->
42 tcCoreLamBndrs vars $ \ vars' ->
43 mapTc tcCoreExpr args `thenTc` \ args' ->
44 tcCoreExpr rhs `thenTc` \ rhs' ->
45 returnTc (emptyLIE, IfaceRuleOut fun' (Rule name vars' args' rhs'))
47 tcRule (IfaceRuleOut fun rule)
48 = tcVar fun `thenTc` \ fun' ->
49 returnTc (emptyLIE, IfaceRuleOut fun' rule)
51 tcRule (HsRule name sig_tvs vars lhs rhs src_loc)
52 = tcAddSrcLoc src_loc $
53 tcAddErrCtxt (ruleCtxt name) $
54 newTyVarTy_OpenKind `thenNF_Tc` \ rule_ty ->
56 -- Deal with the tyvars mentioned in signatures
57 -- Yuk to the UserTyVar
58 mapNF_Tc (tcHsTyVar . UserTyVar) sig_tvs `thenNF_Tc` \ sig_tyvars ->
59 tcExtendTyVarEnv sig_tyvars (
61 -- Ditto forall'd variables
62 mapNF_Tc new_id vars `thenNF_Tc` \ ids ->
63 tcExtendLocalValEnv [(idName id, id) | id <- ids] $
66 tcExpr lhs rule_ty `thenTc` \ (lhs', lhs_lie) ->
67 tcExpr rhs rule_ty `thenTc` \ (rhs', rhs_lie) ->
69 returnTc (ids, lhs', rhs', lhs_lie, rhs_lie)
70 ) `thenTc` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
72 -- Check that LHS has no overloading at all
73 tcSimplifyToDicts lhs_lie `thenTc` \ (lhs_dicts, lhs_binds) ->
74 checkSigTyVars sig_tyvars emptyVarSet `thenTc_`
76 -- Gather the template variables and tyvars
78 tpl_ids = map instToId (bagToList lhs_dicts) ++ ids
80 -- IMPORTANT! We *quantify* over any dicts that appear in the LHS
82 -- a) The particular dictionary isn't important, because its value
83 -- depends only on the type
84 -- e.g gcd Int $fIntegralInt
85 -- Here we'd like to match against (gcd Int any_d) for any 'any_d'
87 -- b) We'd like to make available the dictionaries bound
88 -- on the LHS in the RHS, so quantifying over them is good
89 -- See the 'lhs_dicts' in tcSimplifyAndCheck for the RHS
92 -- Gather type variables to quantify over
93 zonkTcTypes (rule_ty : map idType tpl_ids) `thenNF_Tc` \ zonked_tys ->
95 tpl_tvs = tyVarsOfTypes zonked_tys
98 -- RHS can be a bit more lenient. In particular,
99 -- we let constant dictionaries etc float outwards
100 tcSimplifyAndCheck (text "tcRule") tpl_tvs
101 lhs_dicts rhs_lie `thenTc` \ (lie', rhs_binds) ->
103 returnTc (lie', HsRule name (varSetElems tpl_tvs)
104 (map RuleBndr tpl_ids) -- yuk
105 (mkHsLet lhs_binds lhs')
106 (mkHsLet rhs_binds rhs')
109 new_id (RuleBndr var) = newTyVarTy_OpenKind `thenNF_Tc` \ ty ->
110 returnNF_Tc (mkVanillaId var ty)
111 new_id (RuleBndrSig var rn_ty) = tcHsSigType rn_ty `thenTc` \ ty ->
112 returnNF_Tc (mkVanillaId var ty)
114 ruleCtxt name = ptext SLIT("When checking the transformation rule") <+>
115 doubleQuotes (ptext name)