#include "HsVersions.h"
-import HsSyn ( HsDecl(..), DefaultDecl(..) )
-import RnHsSyn ( RenamedHsDecl )
-
-import TcMonad
-import TcEnv ( tcLookupClassByKey )
+import HsSyn ( DefaultDecl(..) )
+import Name ( Name )
+import TcRnMonad
+import TcEnv ( tcLookupGlobal_maybe )
import TcMonoType ( tcHsType )
-import TcSimplify ( tcSimplifyCheckThetas )
-
-import TysWiredIn ( integerTy, doubleTy )
-import Type ( Type )
-import Unique ( numClassKey )
-import ErrUtils ( addShortErrLocLine )
+import TcSimplify ( tcSimplifyDefault )
+import TcType ( Type, mkClassPred, isTauTy )
+import PrelNames ( numClassName )
import Outputable
-import Util
+import HscTypes ( TyThing(..) )
\end{code}
\begin{code}
-default_default = [integerTy, doubleTy ]
-
-tcDefaults :: [RenamedHsDecl]
- -> TcM s [Type] -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+ -> TcM [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 default_default
-
-tc_defaults [DefaultDecl mono_tys locn]
- = tcAddSrcLoc locn $
- mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
-
- case tau_tys of
- [] -> returnTc [] -- no defaults
-
- _ ->
- -- Check that all the types are instances of Num
- -- We only care about whether it worked or not
- tcAddErrCtxt defaultDeclCtxt $
- tcLookupClassByKey numClassKey `thenNF_Tc` \ num ->
- tcSimplifyCheckThetas
- [{- Nothing given -}]
- [ (num, [ty]) | ty <- tau_tys ] `thenTc_`
-
- returnTc tau_tys
-
-tc_defaults decls@(DefaultDecl _ loc : _) =
- tcAddSrcLoc loc $
+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 [] -- 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 ->
+
+ -- 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
+
+tcDefaults decls@(DefaultDecl _ loc : _) =
+ addSrcLoc loc $
failWithTc (dupDefaultDeclErr decls)
+tc_default_ty hs_ty
+ = tcHsType 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")
4 (vcat (map pp dup_things))
where
pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
+
+polyDefErr ty
+ = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty)
\end{code}
+