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(..), collectRuleBndrSigTys )
12 import CoreSyn ( CoreRule(..) )
13 import RnHsSyn ( RenamedRuleDecl )
14 import TcHsSyn ( TypecheckedRuleDecl, mkHsLet )
16 import TcSimplify ( tcSimplifyToDicts, tcSimplifyInferCheck )
17 import TcMType ( newTyVarTy )
18 import TcType ( 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 )
29 tcRules :: [RenamedRuleDecl] -> TcM [TypecheckedRuleDecl]
30 tcRules decls = mappM tcRule decls
32 tcRule :: RenamedRuleDecl -> TcM TypecheckedRuleDecl
33 tcRule (IfaceRule name act vars fun args rhs src_loc)
35 addErrCtxt (ruleCtxt name) $
36 tcVar fun `thenM` \ fun' ->
37 tcCoreLamBndrs vars $ \ vars' ->
38 mappM tcCoreExpr args `thenM` \ args' ->
39 tcCoreExpr rhs `thenM` \ rhs' ->
40 returnM (IfaceRuleOut fun' (Rule name act vars' args' rhs'))
42 tcRule (IfaceRuleOut fun rule) -- Built-in rules come this way
43 = tcVar fun `thenM` \ fun' ->
44 returnM (IfaceRuleOut fun' rule)
46 tcRule (HsRule name act vars lhs rhs src_loc)
48 addErrCtxt (ruleCtxt name) $
49 newTyVarTy openTypeKind `thenM` \ rule_ty ->
51 -- Deal with the tyvars mentioned in signatures
52 tcAddScopedTyVars (collectRuleBndrSigTys vars) (
54 -- Ditto forall'd variables
55 mappM new_id vars `thenM` \ ids ->
56 tcExtendLocalValEnv ids $
59 getLIE (tcMonoExpr lhs rule_ty) `thenM` \ (lhs', lhs_lie) ->
60 getLIE (tcMonoExpr rhs rule_ty) `thenM` \ (rhs', rhs_lie) ->
62 returnM (ids, lhs', rhs', lhs_lie, rhs_lie)
63 ) `thenM` \ (ids, lhs', rhs', lhs_lie, rhs_lie) ->
65 -- Check that LHS has no overloading at all
66 getLIE (tcSimplifyToDicts lhs_lie) `thenM` \ (lhs_binds, lhs_dicts) ->
68 -- Gather the template variables and tyvars
70 tpl_ids = map instToId lhs_dicts ++ ids
72 -- IMPORTANT! We *quantify* over any dicts that appear in the LHS
74 -- a) The particular dictionary isn't important, because its value
75 -- depends only on the type
76 -- e.g gcd Int $fIntegralInt
77 -- Here we'd like to match against (gcd Int any_d) for any 'any_d'
79 -- b) We'd like to make available the dictionaries bound
80 -- on the LHS in the RHS, so quantifying over them is good
81 -- See the 'lhs_dicts' in tcSimplifyAndCheck for the RHS
83 -- We initially quantify over any tyvars free in *either* the rule
84 -- *or* the bound variables. The latter is important. Consider
85 -- ss (x,(y,z)) = (x,z)
86 -- RULE: forall v. fst (ss v) = fst v
87 -- The type of the rhs of the rule is just a, but v::(a,(b,c))
89 -- It's still conceivable that there may be type variables mentioned
90 -- in the LHS, but not in the type of the lhs, nor in the binders.
91 -- They'll get zapped to (), but that's over-constraining really.
92 -- Let's see if we get a problem.
93 forall_tvs = tyVarsOfTypes (rule_ty : map idType tpl_ids)
96 -- RHS can be a bit more lenient. In particular,
97 -- we let constant dictionaries etc float outwards
100 tcSimplifyInferCheck (text "tcRule")
102 lhs_dicts rhs_lie `thenM` \ (forall_tvs1, rhs_binds) ->
104 returnM (HsRule name act
105 (map RuleBndr (forall_tvs1 ++ tpl_ids)) -- yuk
106 (mkHsLet lhs_binds lhs')
107 (mkHsLet rhs_binds rhs')
110 new_id (RuleBndr var) = newTyVarTy openTypeKind `thenM` \ ty ->
111 returnM (mkLocalId var ty)
112 new_id (RuleBndrSig var rn_ty) = tcHsSigType (RuleSigCtxt var) rn_ty `thenM` \ ty ->
113 returnM (mkLocalId var ty)
115 ruleCtxt name = ptext SLIT("When checking the transformation rule") <+>
116 doubleQuotes (ftext name)