%
-% (c) The AQUA Project, Glasgow University, 1993-1995
+% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[TcDefaults]{Typechecking \tr{default} declarations}
\begin{code}
-#include "HsVersions.h"
-
module TcDefaults ( tcDefaults ) where
-import TcMonad
-import AbsSyn
+#include "HsVersions.h"
-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 TcSimplify ( tcSimplifyCheckThetas )
-import TVE
-import Unique ( numClassKey, Unique )
-import Util
+import HsSyn ( DefaultDecl(..) )
+import Name ( Name )
+import TcRnMonad
+import TcEnv ( tcLookupClass )
+import TcHsType ( tcHsSigType, UserTypeCtxt( DefaultDeclCtxt ) )
+import TcSimplify ( tcSimplifyDefault )
+import TcType ( Type, mkClassPred, isTauTy )
+import PrelNames ( numClassName )
+import Outputable
\end{code}
\begin{code}
-tcDefaults :: E
- -> [RenamedDefaultDecl]
- -> TcM [UniType] -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+ -> TcM (Maybe [Type]) -- Defaulting types to heave
-- into Tc monad for later use
-- in Disambig.
-tcDefaults _ []
- = returnTc [intTy, doubleTy] -- language-specified default `default'
+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 e [DefaultDecl mono_tys locn]
- = let
- ce = getE_CE e
- tce = getE_TCE e
- tve = nullTVE
+tcDefaults [DefaultDecl [] locn]
+ = returnM (Just []) -- Default declaration specifying no types
- num_clas = lookupCE ce (PreludeClass numClassKey (panic "tcDefaults"))
- in
- babyTcMtoTcM (mapB_Tc (tcMonoType ce tce tve) mono_tys) `thenTc` \ tau_tys ->
+tcDefaults [DefaultDecl mono_tys locn]
+ = addSrcLoc 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] `thenM_`
+
+ returnM (Just tau_tys)
- -- compensate for extreme parser hack: `default ()' actually
- -- sends the *type* () through to here. Squash it.
- case tau_tys of
- [ty] | ty == unitTy -> returnTc []
+tcDefaults decls@(DefaultDecl _ loc : _) =
+ addSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)
- _ -> -- (Back to your regularly scheduled programming...)
- -- Check that all the types are instances of Num
+tc_default_ty hs_ty
+ = tcHsSigType DefaultDeclCtxt hs_ty `thenM` \ ty ->
+ checkTc (isTauTy ty) (polyDefErr hs_ty) `thenM_`
+ returnM ty
- tcSimplifyCheckThetas (DefaultDeclOrigin locn)
- [ (num_clas, ty) | ty <- tau_tys ] `thenTc` \ _ ->
- -- We only care about whether it worked or not
+defaultDeclCtxt = ptext SLIT("when checking that each type in a default declaration")
+ $$ ptext SLIT("is an instance of class Num")
- returnTc tau_tys -- caller will bung them into Tc monad
-tcDefaults _ (_:_)
- = error "ERROR: You can only have one `default' declaration per module."
- -- ToDo: proper error msg.
+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
+
+polyDefErr ty
+ = hang (ptext SLIT("Illegal polymorphic type in default declaration") <> colon) 4 (ppr ty)
\end{code}
+