\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
-module TcDefaults ( tcDefaults, defaultDefaultTys ) where
+module TcDefaults ( tcDefaults ) where
#include "HsVersions.h"
-import HsSyn ( HsDecl(..), DefaultDecl(..) )
-import RnHsSyn ( RenamedHsDecl )
-
-import TcMonad
-import TcEnv ( tcLookupGlobal_maybe )
-import TcMonoType ( tcHsType )
+import HsSyn ( DefaultDecl(..), LDefaultDecl )
+import Name ( Name )
+import TcRnMonad
+import TcEnv ( tcLookupClass )
+import TcHsType ( tcHsSigType, UserTypeCtxt( DefaultDeclCtxt ) )
import TcSimplify ( tcSimplifyDefault )
-
-import TysWiredIn ( integerTy, doubleTy )
import TcType ( Type, mkClassPred, isTauTy )
import PrelNames ( numClassName )
+import SrcLoc ( Located(..) )
import Outputable
-import HscTypes ( TyThing(..) )
\end{code}
\begin{code}
-defaultDefaultTys = [integerTy, doubleTy]
-
-tcDefaults :: [RenamedHsDecl]
- -> TcM [Type] -- defaulting types to heave
+tcDefaults :: [LDefaultDecl Name]
+ -> TcM (Maybe [Type]) -- Defaulting types to heave
-- into Tc monad for later use
-- in Disambig.
-tcDefaults decls = tc_defaults [default_decl | DefD default_decl <- decls]
-tc_defaults [] = returnTc defaultDefaultTys
-
-tc_defaults [DefaultDecl [] locn]
- = returnTc [] -- no defaults
-
-tc_defaults [DefaultDecl mono_tys locn]
- = tcLookupGlobal_maybe numClassName `thenNF_Tc` \ maybe_num ->
- case maybe_num of
- Just (AClass num_class) -> common_case num_class
- other -> returnTc []
- -- 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
- = tcAddSrcLoc locn $
- tcAddErrCtxt defaultDeclCtxt $
- mapTc tc_default_ty mono_tys `thenTc` \ tau_tys ->
+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 [L locn (DefaultDecl [])]
+ = returnM (Just []) -- Default declaration specifying no types
+
+tcDefaults [L locn (DefaultDecl mono_tys)]
+ = setSrcSpan 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] `thenTc_`
+ -- 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_`
- returnTc tau_tys
+ returnM (Just tau_tys)
-tc_defaults decls@(DefaultDecl _ loc : _) =
- tcAddSrcLoc loc $
+tcDefaults decls@(L locn (DefaultDecl _) : _) =
+ setSrcSpan locn $
failWithTc (dupDefaultDeclErr decls)
tc_default_ty hs_ty
- = tcHsType hs_ty `thenTc` \ ty ->
- checkTc (isTauTy ty) (polyDefErr hs_ty) `thenTc_`
- returnTc ty
+ = tcHsSigType DefaultDeclCtxt hs_ty `thenM` \ ty ->
+ checkTc (isTauTy ty) (polyDefErr hs_ty) `thenM_`
+ returnM ty
defaultDeclCtxt = ptext SLIT("when checking that each type in a default declaration")
$$ ptext SLIT("is an instance of class Num")
-dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
+dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
= hang (ptext SLIT("Multiple default declarations"))
4 (vcat (map pp dup_things))
where
- pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
+ pp (L locn (DefaultDecl _)) = ptext SLIT("here was another default declaration") <+> ppr locn
polyDefErr ty
= hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty)