[project @ 1999-12-20 10:34:27 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 3d40162..a3c292b 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,55 +1,81 @@
 %
-% (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
 
-IMP_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}
+