[project @ 1998-12-02 13:17:09 by simonm]

[ghc-hetmet.git] / ghc / compiler / typecheck / TcDefaults.lhs

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 0296080..7335631 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,43 +1,43 @@
 %
-% (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 TcMonad
 import TcEnv           ( tcLookupClassByKey )
-import TcMonoType      ( tcMonoType )
+import TcMonoType      ( tcHsType )
 import TcSimplify      ( tcSimplifyCheckThetas )
 
-import PrelInfo                ( intTy, doubleTy, unitTy )
+import TysWiredIn      ( intTy, doubleTy )
+import Type             ( Type )
 import Unique          ( numClassKey )
+import ErrUtils                ( addShortErrLocLine )
+import Outputable
 import Util
 \end{code}
 
 \begin{code}
-tcDefaults :: [RenamedDefaultDecl]
+default_default = [intTy, doubleTy]        -- language-specified default `default'
+
+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 [DefaultDecl mono_tys locn]
+tc_defaults [DefaultDecl mono_tys locn]
   = tcAddSrcLoc locn $
-    mapTc tcMonoType mono_tys  `thenTc` \ tau_tys ->
+    mapTc tcHsType mono_tys    `thenTc` \ tau_tys ->
 
     case tau_tys of
       [] -> returnTc []                -- no defaults
@@ -46,10 +46,28 @@ tcDefaults [DefaultDecl mono_tys locn]
            -- Check that all the types are instances of Num
            -- We only care about whether it worked or not
 
-       tcLookupClassByKey numClassKey                  `thenNF_Tc` \ num ->
-       tcSimplifyCheckThetas DefaultDeclOrigin
-               [ (num, ty) | ty <- tau_tys ]           `thenTc` \ _ ->
+       tcAddErrCtxt defaultDeclCtxt            $
+       tcLookupClassByKey numClassKey          `thenNF_Tc` \ num ->
+       tcSimplifyCheckThetas
+               [{- Nothing given -}]
+               [ (num, [ty]) | ty <- tau_tys ] `thenTc_`
 
        returnTc tau_tys
 
+tc_defaults decls
+  = 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)
+  = vcat (item1 : map dup_item dup_things)
+  where
+    item1
+      = addShortErrLocLine locn1 (ptext SLIT("multiple default declarations"))
+
+    dup_item (DefaultDecl _ locn)
+      = addShortErrLocLine locn (ptext SLIT("here was another default declaration"))
 \end{code}