%
-% (c) The AQUA Project, Glasgow University, 1993-1995
+% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
-module TcDefaults ( tcDefaults ) where
+module TcDefaults ( tcDefaults, defaultDefaultTys ) where
#include "HsVersions.h"
import HsSyn ( HsDecl(..), DefaultDecl(..) )
-import RnHsSyn ( RenamedHsDecl(..), RenamedDefaultDecl(..) )
+import RnHsSyn ( RenamedHsDecl )
import TcMonad
-import Inst ( InstOrigin(..) )
-import TcEnv ( TcIdOcc, tcLookupClassByKey )
+import TcEnv ( tcLookupGlobal_maybe )
import TcMonoType ( tcHsType )
import TcSimplify ( tcSimplifyCheckThetas )
-import TysWiredIn ( intTy, doubleTy, unitTy )
-import Type ( Type )
-import Unique ( numClassKey )
-import ErrUtils ( addShortErrLocLine )
+import TysWiredIn ( integerTy, doubleTy )
+import TcType ( Type, mkClassPred )
+import PrelNames ( numClassName )
import Outputable
-import Util
+import HscTypes ( TyThing(..) )
\end{code}
\begin{code}
-default_default = [intTy, doubleTy] -- language-specified default `default'
+defaultDefaultTys = [integerTy, doubleTy]
tcDefaults :: [RenamedHsDecl]
- -> TcM s [Type] -- defaulting types to heave
+ -> 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 [] = returnTc defaultDefaultTys
-tc_defaults [DefaultDecl mono_tys locn]
- = tcAddSrcLoc locn $
- mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
-
- case tau_tys of
- [] -> returnTc [] -- no defaults
+tc_defaults [DefaultDecl [] locn]
+ = 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_`
+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 $
+ mapTc tcHsType 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 -}]
+ [ mkClassPred num_class [ty] | ty <- tau_tys ] `thenTc_`
+
+ returnTc tau_tys
- returnTc tau_tys
-tc_defaults decls
- = failWithTc (dupDefaultDeclErr decls)
+tc_defaults decls@(DefaultDecl _ loc : _) =
+ tcAddSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)
defaultDeclCtxt = ptext SLIT("when checking that each type in a default declaration")
dupDefaultDeclErr (DefaultDecl _ locn1 : dup_things)
- = vcat (item1 : map dup_item dup_things)
+ = hang (ptext SLIT("Multiple default declarations"))
+ 4 (vcat (map pp dup_things))
where
- item1
- = addShortErrLocLine locn1 (ptext SLIT("multiple default declarations"))
-
- dup_item (DefaultDecl _ locn)
- = addShortErrLocLine locn (ptext SLIT("here was another default declaration"))
+ pp (DefaultDecl _ locn) = ptext SLIT("here was another default declaration") <+> ppr locn
\end{code}
+