[project @ 2003-07-21 15:14:18 by ross]

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

diff --git a/ghc/compiler/typecheck/TcDefaults.lhs b/ghc/compiler/typecheck/TcDefaults.lhs
index 811f04b..f107451 100644 (file)
--- a/ghc/compiler/typecheck/TcDefaults.lhs
+++ b/ghc/compiler/typecheck/TcDefaults.lhs
@@ -1,67 +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 TcMonad
-import AbsSyn
+#include "HsVersions.h"
 
-import AbsPrel         ( intTy, doubleTy, unitTy )
-import AbsUniType      ( UniType
-                         IF_ATTACK_PRAGMAS(COMMA cmpUniType)
-                       )
-import CE              ( lookupCE, CE(..) )
-import E
-import Inst
-import Name
-import TcMonoType      ( tcMonoType )
-import TcSimplify      ( tcSimplifyCheckThetas )
-import TVE
-import Unique          ( numClassKey, Unique )
-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 :: E
-          -> [RenamedDefaultDecl]
-          -> TcM [UniType]         -- 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 e [DefaultDecl mono_tys locn]
-  = let
-       ce  = getE_CE  e
-       tce = getE_TCE e
-       tve = nullTVE
+tcDefaults [DefaultDecl [] locn]
+  = returnM []                 -- Default declaration specifying no types
 
-       num_clas = lookupCE ce (PreludeClass numClassKey (panic "tcDefaults"))
-    in
-    babyTcMtoTcM (mapB_Tc (tcMonoType ce tce tve) mono_tys) `thenTc` \ tau_tys ->
+tcDefaults [DefaultDecl mono_tys locn]
+  = 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
 
-       -- compensate for extreme parser hack: `default ()' actually
-       -- sends the *type* () through to here.  Squash it.
-    case tau_tys of
-      [ty] | ty == unitTy -> returnTc []
+tcDefaults decls@(DefaultDecl _ loc : _) =
+    addSrcLoc loc $
+    failWithTc (dupDefaultDeclErr decls)
 
-      _  -> -- (Back to your regularly scheduled programming...)
 
-           -- Check that all the types are instances of Num
+tc_default_ty hs_ty 
+ = tcHsType hs_ty                              `thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)     `thenM_`
+   returnM ty
 
-       tcSimplifyCheckThetas (DefaultDeclOrigin locn)
-                        [ (num_clas, ty) | ty <- tau_tys ] `thenTc` \ _ ->
-           -- We only care about whether it worked or not
+defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
+                   $$ ptext SLIT("is an instance of class Num")
 
-       returnTc tau_tys -- caller will bung them into Tc monad
 
-tcDefaults _ (_:_)
-  = error "ERROR: You can only have one `default' declaration per module."
-    -- ToDo: proper error msg.
+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}
+