orCond :: Condition -> Condition -> Condition
orCond c1 c2 tc
= case c1 tc of
- Nothing -> Nothing -- c1 succeeds
- Just {} -> c2 tc -- c1 fails, try c2
--- orCond produced just one error message, namely from c2
--- Getting two can be confusing. For a zero-constructor
--- type with a standalone isntance decl, we previously got:
--- Can't make a derived instance of `Bounded (Test a)':
--- `Test' has no data constructors
--- and
--- `Test' does not have precisely one constructor
+ Nothing -> Nothing -- c1 succeeds
+ Just x -> case c2 tc of -- c1 fails
+ Nothing -> Nothing
+ Just y -> Just (x $$ ptext (sLit " and") $$ y)
+ -- Both fail
andCond :: Condition -> Condition -> Condition
andCond c1 c2 tc = case c1 tc of
cond_isEnumeration :: Condition
cond_isEnumeration (_, rep_tc)
- | null (tyConDataCons rep_tc) = Just (no_cons_why rep_tc)
| isEnumerationTyCon rep_tc = Nothing
| otherwise = Just why
where
- why = quotes (pprSourceTyCon rep_tc) <+>
- ptext (sLit "has non-nullary constructors")
+ why = sep [ quotes (pprSourceTyCon rep_tc) <+>
+ ptext (sLit "is not an enumeration type")
+ , nest 2 $ ptext (sLit "(an enumeration consists of one or more nullary constructors)") ]
+ -- See Note [Enumeration types] in TyCon
cond_isProduct :: Condition
cond_isProduct (_, rep_tc)