import HsSyn ( DefaultDecl(..) )
import Name ( Name )
import TcRnMonad
-import TcEnv ( tcLookupGlobal_maybe )
-import TcMonoType ( tcHsType )
+import TcEnv ( tcLookupClass )
+import TcHsType ( tcHsSigType, UserTypeCtxt( DefaultDeclCtxt ) )
import TcSimplify ( tcSimplifyDefault )
import TcType ( Type, mkClassPred, isTauTy )
import PrelNames ( numClassName )
import Outputable
-import HscTypes ( TyThing(..) )
\end{code}
\begin{code}
tcDefaults :: [DefaultDecl Name]
- -> TcM [Type] -- defaulting types to heave
+ -> TcM (Maybe [Type]) -- Defaulting types to heave
-- into Tc monad for later use
-- in Disambig.
-tcDefaults [] = returnM defaultDefaultTys
+tcDefaults []
+ = getDefaultTys -- No default declaration, so get the
+ -- default types from the envt;
+ -- i.e. use the curent ones
+ -- (the caller will put them back there)
+ -- It's important not to return defaultDefaultTys here (which
+ -- we used to do) because in a TH program, tcDefaults [] is called
+ -- repeatedly, once for each group of declarations between top-level
+ -- splices. We don't want to carefully set the default types in
+ -- one group, only for the next group to ignore them and install
+ -- defaultDefaultTys
tcDefaults [DefaultDecl [] locn]
- = returnM [] -- no defaults
+ = returnM (Just []) -- Default declaration specifying no types
tcDefaults [DefaultDecl mono_tys locn]
- = tcLookupGlobal_maybe numClassName `thenM` \ maybe_num ->
- case maybe_num of
- Just (AClass num_class) -> common_case num_class
- other -> returnM []
- -- In the Nothing case, Num has not been sucked in, so the
- -- defaults will never be used; so simply discard the default decl.
- -- This slightly benefits modules that don't use any
- -- numeric stuff at all, by avoid the necessity of
- -- always sucking in Num
- where
- common_case num_class
- = addSrcLoc locn $
- addErrCtxt defaultDeclCtxt $
- mappM tc_default_ty mono_tys `thenM` \ tau_tys ->
+ = addSrcLoc locn $
+ addErrCtxt defaultDeclCtxt $
+ tcLookupClass numClassName `thenM` \ num_class ->
+ mappM tc_default_ty mono_tys `thenM` \ tau_tys ->
- -- Check that all the types are instances of Num
- -- We only care about whether it worked or not
- tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys] `thenM_`
+ -- Check that all the types are instances of Num
+ -- We only care about whether it worked or not
+ tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys] `thenM_`
- returnM tau_tys
+ returnM (Just tau_tys)
tcDefaults decls@(DefaultDecl _ loc : _) =
addSrcLoc loc $
tc_default_ty hs_ty
- = tcHsType hs_ty `thenM` \ ty ->
+ = tcHsSigType DefaultDeclCtxt hs_ty `thenM` \ ty ->
checkTc (isTauTy ty) (polyDefErr hs_ty) `thenM_`
returnM ty