%
-% (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
+
#include "HsVersions.h"
-module TcDefaults ( tcDefaults ) where
+import HsSyn ( HsDecl(..), DefaultDecl(..) )
+import RnHsSyn ( RenamedHsDecl )
import TcMonad
-import AbsSyn
-
-import AbsPrel ( intTy, doubleTy, unitTy )
-import AbsUniType ( UniType
- IF_ATTACK_PRAGMAS(COMMA cmpUniType)
- )
-import CE ( lookupCE, CE(..) )
-import E
-import Inst
-import Name
-import TcMonoType ( tcMonoType )
+import TcEnv ( tcLookupClassByKey_maybe )
+import TcMonoType ( tcHsType )
import TcSimplify ( tcSimplifyCheckThetas )
-import TVE
-import Unique ( numClassKey, Unique )
+
+import TysWiredIn ( integerTy, doubleTy )
+import Type ( Type )
+import Unique ( numClassKey )
+import ErrUtils ( addShortErrLocLine )
+import Outputable
import Util
\end{code}
\begin{code}
-tcDefaults :: E
- -> [RenamedDefaultDecl]
- -> TcM [UniType] -- defaulting types to heave
+default_default = [integerTy, doubleTy]
+
+tcDefaults :: [RenamedHsDecl]
+ -> TcM s [Type] -- defaulting types to heave
-- into Tc monad for later use
-- in Disambig.
+tcDefaults decls = tc_defaults [default_decl | DefD default_decl <- decls]
-tcDefaults _ []
- = returnTc [intTy, doubleTy] -- language-specified default `default'
+tc_defaults [] = returnTc default_default
-tcDefaults e [DefaultDecl mono_tys locn]
- = let
- ce = getE_CE e
- tce = getE_TCE e
- tve = nullTVE
+tc_defaults [DefaultDecl [] locn]
+ = returnTc [] -- no defaults
- num_clas = lookupCE ce (PreludeClass numClassKey (panic "tcDefaults"))
- in
- babyTcMtoTcM (mapB_Tc (tcMonoType ce tce tve) mono_tys) `thenTc` \ tau_tys ->
+tc_defaults [DefaultDecl mono_tys locn]
+ = tcLookupClassByKey_maybe numClassKey `thenNF_Tc` \ maybe_num ->
+ case maybe_num of {
+ Nothing -> -- 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
+ returnTc [] ;
- -- compensate for extreme parser hack: `default ()' actually
- -- sends the *type* () through to here. Squash it.
- case tau_tys of
- [ty] | ty == unitTy -> returnTc []
+ Just num -> -- The common case
- _ -> -- (Back to your regularly scheduled programming...)
+ tcAddSrcLoc locn $
+ mapTc tcHsType mono_tys `thenTc` \ tau_tys ->
-- Check that all the types are instances of Num
-
- tcSimplifyCheckThetas (DefaultDeclOrigin locn)
- [ (num_clas, ty) | ty <- tau_tys ] `thenTc` \ _ ->
-- We only care about whether it worked or not
+ tcAddErrCtxt defaultDeclCtxt $
+ tcSimplifyCheckThetas
+ [{- Nothing given -}]
+ [ (num, [ty]) | ty <- tau_tys ] `thenTc_`
- returnTc tau_tys -- caller will bung them into Tc monad
+ returnTc tau_tys
+ }
-tcDefaults _ (_:_)
- = error "ERROR: You can only have one `default' declaration per module."
- -- ToDo: proper error msg.
+tc_defaults decls@(DefaultDecl _ loc : _) =
+ tcAddSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)
+
+
+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)
+ = 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
\end{code}
+