= return fun -- Common short cut
instFun orig fun subst tv_theta_prs
- = do { -- !!!SPJ: -- Horrid check for tagToEnum; see Note [tagToEnum#]
- -- !!!SPJ: checkBadTagToEnumCall fun_id qtv_tys
+ = do { let ty_theta_prs' = map subst_pr tv_theta_prs
- ; let ty_theta_prs' = map subst_pr tv_theta_prs
-
- -- First, chuck in the constraints from
- -- the "stupid theta" of a data constructor (sigh)
- ; inst_stupid fun ty_theta_prs'
+ -- Make two ad-hoc checks
+ ; doStupidChecks orig fun ty_theta_prs'
-- Now do normal instantiation
; go True fun ty_theta_prs' }
subst_pr (tvs, theta)
= (map (substTyVar subst) tvs, substTheta subst theta)
- inst_stupid (HsVar fun_id) ((tys,_):_)
- | Just con <- isDataConId_maybe fun_id
- = addDataConStupidTheta orig con tys
- inst_stupid _ _ = return ()
-
go _ fun [] = return fun
go True (HsVar fun_id) ((tys,theta) : prs)
\begin{code}
-checkBadTagToEnumCall :: Id -> [TcType] -> TcM ()
-checkBadTagToEnumCall fun_id tys
- | fun_id `hasKey` tagToEnumKey
+doStupidChecks :: InstOrigin
+ -> HsExpr TcId
+ -> [([TcType], ThetaType)]
+ -> TcM ()
+-- Check two tiresome and ad-hoc cases
+-- (a) the "stupid theta" for a data con; add the constraints
+-- from the "stupid theta" of a data constructor (sigh)
+-- (b) deal with the tagToEnum# problem: see Note [tagToEnum#]
+
+doStupidChecks orig (HsVar fun_id) ((tys,_):_)
+ | Just con <- isDataConId_maybe fun_id -- (a)
+ = addDataConStupidTheta orig con tys
+
+ | fun_id `hasKey` tagToEnumKey -- (b)
= do { tys' <- zonkTcTypes tys
; checkTc (ok tys') (tagToEnumError tys')
}
- | otherwise -- Vastly common case
- = return ()
where
ok [] = False
ok (ty:tys) = case tcSplitTyConApp_maybe ty of
Just (tc,_) -> isEnumerationTyCon tc
Nothing -> False
+doStupidChecks orig fun tv_theta_prs
+ = return () -- The common case
+
+
tagToEnumError tys
= hang (ptext SLIT("Bad call to tagToEnum#") <+> at_type)
2 (vcat [ptext SLIT("Specify the type by giving a type signature"),