[project @ 2003-06-27 21:17:24 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 d714ddd..f107451 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,55 +1,89 @@
 %
-% (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(..) )
+import Name            ( Name )
+import TcRnMonad
+import TcEnv           ( tcLookupGlobal_maybe )
+import TcMonoType      ( tcHsType )
+import TcSimplify      ( tcSimplifyDefault )
+import TcType           ( Type, mkClassPred, isTauTy )
+import PrelNames       ( numClassName )
+import Outputable
+import HscTypes                ( TyThing(..) )
 \end{code}
 
 \begin{code}
-tcDefaults :: [RenamedDefaultDecl]
-          -> TcM s [Type]          -- defaulting types to heave
+tcDefaults :: [DefaultDecl Name]
+          -> TcM [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 [] locn]
+  = returnM []                 -- Default declaration specifying no types
 
 tcDefaults [DefaultDecl mono_tys locn]
-  = tcAddSrcLoc locn $
-    mapTc tcMonoType mono_tys  `thenTc` \ tau_tys ->
+  = tcLookupGlobal_maybe numClassName  `thenM` \ maybe_num ->
+    case maybe_num of
+       Just (AClass num_class) -> common_case num_class
+       other                   -> returnM []
+               -- In the Nothing case, 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
+  where
+    common_case num_class
+      = addSrcLoc locn                 $
+       addErrCtxt defaultDeclCtxt      $
+       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 tau_tys
+
+tcDefaults decls@(DefaultDecl _ loc : _) =
+    addSrcLoc loc $
+    failWithTc (dupDefaultDeclErr decls)
 
-    case tau_tys of
-      [] -> returnTc []                -- no defaults
 
-      _  ->
-           -- Check that all the types are instances of Num
-           -- We only care about whether it worked or not
+tc_default_ty hs_ty 
+ = tcHsType hs_ty                              `thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)     `thenM_`
+   returnM ty
 
-       tcLookupClassByKey numClassKey                  `thenNF_Tc` \ num ->
-       tcSimplifyCheckThetas
-               [ (num, ty) | ty <- tau_tys ]           `thenTc_`
+defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
+                   $$ ptext SLIT("is an instance of class Num")
 
-       returnTc tau_tys
 
+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}
+