import Class
import Var
import CoreUnfold ( mkDFunUnfolding )
+import CoreUtils ( mkPiTypes )
import PrelNames ( inlineIdName )
import Id
import MkId
The INLINE on df is vital, else $cop_list occurs just once and is inlined,
which is a disaster if $cop_list *itself* has an INLINE pragma.
+Notice, also, that we go to the trouble of generating a complicated cast,
+rather than do this:
+ df = /\a. \d. MkD ($cop_list a d)
+where the MkD "constructor" willl expand to a suitable cast:
+ df = /\a. \d. ($cop_list a d) |> (...)
+Reason: suppose $cop_list has an INLINE pragma. We want to avoid the
+nasty possibility that we eta-expand df, to get
+ df = (/\a \d \x. $cop_list a d x) |> (...)
+and now $cop_list may get inlined into the df, rather than at
+the actual call site. Of course, eta reduction may get there first,
+but it seems less fragile to generate the Right Thing in the first place.
+See Trac #3772.
+
Note [Subtle interaction of recursion and overlap]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
; checkSigTyVars inst_tyvars'
-- Create the result bindings
- ; let dict_constr = classDataCon clas
- this_dict_id = instToId this_dict
- dict_bind = mkVarBind this_dict_id dict_rhs
- dict_rhs = foldl mk_app inst_constr (sc_ids ++ meth_ids)
- inst_constr = L loc $ wrapId (mkWpTyApps inst_tys')
- (dataConWrapId dict_constr)
- -- We don't produce a binding for the dict_constr; instead we
- -- rely on the simplifier to unfold this saturated application
- -- We do this rather than generate an HsCon directly, because
- -- it means that the special cases (e.g. dictionary with only one
- -- member) are dealt with by the common MkId.mkDataConWrapId code rather
- -- than needing to be repeated here.
-
- mk_app :: LHsExpr Id -> Id -> LHsExpr Id
- mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id)))
- arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
-
- dfun_id_w_fun | isNewTyCon (classTyCon clas)
- = dfun_id -- Just let the dfun inline; see Note [Single-method classes]
- `setInlinePragma` alwaysInlinePragma
- | otherwise
- = dfun_id -- Do not inline; instead give it a magic DFunFunfolding
- -- See Note [ClassOp/DFun selection]
- `setIdUnfolding` mkDFunUnfolding dict_constr (sc_ids ++ meth_ids)
- `setInlinePragma` dfunInlinePragma
-
- main_bind = noLoc $ AbsBinds
- inst_tyvars'
- dfun_lam_vars
- [(inst_tyvars', dfun_id_w_fun, this_dict_id, spec_inst_prags)]
- (unitBag dict_bind)
+ ; let this_dict_id = instToId this_dict
+ arg_ids = sc_ids ++ meth_ids
+ arg_binds = listToBag meth_binds `unionBags`
+ listToBag sc_binds
; showLIE (text "instance")
- ; return (unitBag main_bind `unionBags`
- listToBag meth_binds `unionBags`
- listToBag sc_binds) }
+ ; case newTyConCo_maybe (classTyCon clas) of
+ Nothing -- A multi-method class
+ -> return (unitBag (L loc data_bind) `unionBags` arg_binds)
+ where
+ data_dfun_id = dfun_id -- Do not inline; instead give it a magic DFunFunfolding
+ -- See Note [ClassOp/DFun selection]
+ `setIdUnfolding` mkDFunUnfolding dict_constr arg_ids
+ `setInlinePragma` dfunInlinePragma
+
+ data_bind = AbsBinds inst_tyvars' dfun_lam_vars
+ [(inst_tyvars', data_dfun_id, this_dict_id, spec_inst_prags)]
+ (unitBag dict_bind)
+
+ dict_bind = mkVarBind this_dict_id dict_rhs
+ dict_rhs = foldl mk_app inst_constr arg_ids
+ dict_constr = classDataCon clas
+ inst_constr = L loc $ wrapId (mkWpTyApps inst_tys')
+ (dataConWrapId dict_constr)
+ -- We don't produce a binding for the dict_constr; instead we
+ -- rely on the simplifier to unfold this saturated application
+ -- We do this rather than generate an HsCon directly, because
+ -- it means that the special cases (e.g. dictionary with only one
+ -- member) are dealt with by the common MkId.mkDataConWrapId code rather
+ -- than needing to be repeated here.
+
+ mk_app :: LHsExpr Id -> Id -> LHsExpr Id
+ mk_app fun arg_id = L loc (HsApp fun (L loc (wrapId arg_wrapper arg_id)))
+ arg_wrapper = mkWpApps dfun_lam_vars <.> mkWpTyApps (mkTyVarTys inst_tyvars')
+
+ Just the_nt_co -- (Just co) for a single-method class
+ -> return (unitBag (L loc nt_bind) `unionBags` arg_binds)
+ where
+ nt_dfun_id = dfun_id -- Just let the dfun inline; see Note [Single-method classes]
+ `setInlinePragma` alwaysInlinePragma
+
+ local_nt_dfun = setIdType this_dict_id inst_ty -- A bit of a hack, but convenient
+
+ nt_bind = AbsBinds [] []
+ [([], nt_dfun_id, local_nt_dfun, spec_inst_prags)]
+ (unitBag (mkVarBind local_nt_dfun (L loc (wrapId nt_cast the_meth_id))))
+
+ the_meth_id = ASSERT( length arg_ids == 1 ) head arg_ids
+ nt_cast = WpCast $ mkPiTypes (inst_tyvars' ++ dfun_lam_vars) $
+ mkSymCoercion (mkTyConApp the_nt_co inst_tys')
+ }
------------------------------
That is important to allow the mutual recursion between $fooInt and
$cop1 to be broken
-This is all regrettably delicate.
-
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%* *