%
-% (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
+#include "HsVersions.h"
-import HsSyn ( DefaultDecl(..), MonoType,
- HsExpr, HsLit, ArithSeqInfo, Fake, InPat)
-import RnHsSyn ( RenamedDefaultDecl(..) )
-import TcHsSyn ( TcIdOcc )
+import HsSyn ( HsDecl(..), DefaultDecl(..) )
+import RnHsSyn ( RenamedHsDecl )
-import TcMonad hiding ( rnMtoTcM )
-import Inst ( InstOrigin(..) )
-import TcEnv ( tcLookupClassByKey )
-import TcMonoType ( tcMonoType )
+import TcMonad
+import TcEnv ( tcLookupClassByKey_maybe )
+import TcMonoType ( tcHsType )
import TcSimplify ( tcSimplifyCheckThetas )
-import TysWiredIn ( intTy, doubleTy, unitTy )
+import TysWiredIn ( integerTy, doubleTy )
+import Type ( Type )
import Unique ( numClassKey )
+import ErrUtils ( addShortErrLocLine )
+import Outputable
import Util
\end{code}
\begin{code}
-tcDefaults :: [RenamedDefaultDecl]
+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]
+
+tc_defaults [] = returnTc default_default
-tcDefaults []
- = returnTc [intTy, doubleTy] -- language-specified default `default'
+tc_defaults [DefaultDecl [] locn]
+ = returnTc [] -- no defaults
-tcDefaults [DefaultDecl mono_tys locn]
- = tcAddSrcLoc locn $
- mapTc tcMonoType 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 [] ;
- case tau_tys of
- [] -> returnTc [] -- no defaults
+ Just num -> -- The common case
+
+ 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 -}]
+ [ (num, [ty]) | ty <- tau_tys ] `thenTc_`
+
+ returnTc tau_tys
+ }
+
+tc_defaults decls@(DefaultDecl _ loc : _) =
+ tcAddSrcLoc loc $
+ failWithTc (dupDefaultDeclErr decls)
- tcLookupClassByKey numClassKey `thenNF_Tc` \ num ->
- tcSimplifyCheckThetas
- [ (num, ty) | ty <- tau_tys ] `thenTc_`
- returnTc tau_tys
+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}
+