%
-% (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 Ubiq
-
-import HsSyn ( DefaultDecl(..), MonoType,
- HsExpr, HsLit, ArithSeqInfo, Fake, InPat)
-import RnHsSyn ( RenamedDefaultDecl(..) )
-import TcHsSyn ( TcIdOcc )
-
-import TcMonad hiding ( rnMtoTcM )
-import Inst ( InstOrigin(..) )
-import TcEnv ( tcLookupClassByKey )
-import TcMonoType ( tcMonoType )
-import TcSimplify ( tcSimplifyCheckThetas )
+#include "HsVersions.h"
-import PrelInfo ( intTy, doubleTy, unitTy )
-import Unique ( numClassKey )
-import Util
+import HsSyn ( DefaultDecl(..), LDefaultDecl )
+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 SrcLoc ( Located(..) )
+import Outputable
\end{code}
\begin{code}
-tcDefaults :: [RenamedDefaultDecl]
- -> TcM s [Type] -- defaulting types to heave
+tcDefaults :: [LDefaultDecl 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 [DefaultDecl mono_tys locn]
- = tcAddSrcLoc locn $
- mapTc tcMonoType mono_tys `thenTc` \ tau_tys ->
+tcDefaults [L locn (DefaultDecl [])]
+ = returnM (Just []) -- Default declaration specifying no types
- case tau_tys of
- [] -> returnTc [] -- no defaults
+tcDefaults [L locn (DefaultDecl mono_tys)]
+ = setSrcSpan 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)
- _ ->
- -- Check that all the types are instances of Num
- -- We only care about whether it worked or not
+tcDefaults decls@(L locn (DefaultDecl _) : _) =
+ setSrcSpan locn $
+ failWithTc (dupDefaultDeclErr decls)
- tcLookupClassByKey numClassKey `thenNF_Tc` \ num ->
- tcSimplifyCheckThetas DefaultDeclOrigin
- [ (num, ty) | ty <- tau_tys ] `thenTc` \ _ ->
- returnTc tau_tys
+tc_default_ty hs_ty
+ = tcHsSigType DefaultDeclCtxt 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")
+
+
+dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
+ = hang (ptext SLIT("Multiple default declarations"))
+ 4 (vcat (map pp dup_things))
+ where
+ pp (L locn (DefaultDecl _)) = 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}
+