\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
-module TcDefaults ( tcDefaults ) where
+module TcDefaults ( tcDefaults, defaultDefaultTys ) where
#include "HsVersions.h"
import TcMonad
import TcEnv ( tcLookupGlobal_maybe )
import TcMonoType ( tcHsType )
-import TcSimplify ( tcSimplifyCheckThetas )
+import TcSimplify ( tcSimplifyDefault )
import TysWiredIn ( integerTy, doubleTy )
-import Type ( Type )
-import PrelNames ( numClassKey )
+import TcType ( Type, mkClassPred, isTauTy )
+import PrelNames ( numClassName )
import Outputable
+import HscTypes ( TyThing(..) )
\end{code}
\begin{code}
-default_default = [integerTy, doubleTy]
+defaultDefaultTys = [integerTy, doubleTy]
tcDefaults :: [RenamedHsDecl]
-> TcM [Type] -- defaulting types to heave
-- in Disambig.
tcDefaults decls = tc_defaults [default_decl | DefD default_decl <- decls]
-tc_defaults [] = returnTc default_default
+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 {
+ case maybe_num of
Just (AClass num_class) -> common_case num_class
- other -> returnTc [] ;
+ 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
-- always sucking in Num
where
common_case num_class
- = tcAddSrcLoc locn $
- mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
+ = tcAddSrcLoc locn $
+ tcAddErrCtxt defaultDeclCtxt $
+ mapTc tc_default_ty mono_tys `thenTc` \ tau_tys ->
-- Check that all the types are instances of Num
-- We only care about whether it worked or not
- tcAddErrCtxt defaultDeclCtxt $
- tcSimplifyCheckThetas
- [{- Nothing given -}]
- [ (num_class, [ty]) | ty <- tau_tys ] `thenTc_`
+ tcSimplifyDefault [mkClassPred num_class [ty] | ty <- tau_tys] `thenTc_`
returnTc tau_tys
- }
tc_defaults decls@(DefaultDecl _ loc : _) =
tcAddSrcLoc loc $
failWithTc (dupDefaultDeclErr decls)
+tc_default_ty hs_ty
+ = tcHsType hs_ty `thenTc` \ ty ->
+ checkTc (isTauTy ty) (polyDefErr hs_ty) `thenTc_`
+ returnTc 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}