Reorganisation of the source tree

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

diff --git a/compiler/typecheck/TcDefaults.lhs b/compiler/typecheck/TcDefaults.lhs
new file mode 100644 (file)
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+++ b/compiler/typecheck/TcDefaults.lhs
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+%
+% (c) The AQUA Project, Glasgow University, 1993-1998
+%
+\section[TcDefaults]{Typechecking \tr{default} declarations}
+
+\begin{code}
+module TcDefaults ( tcDefaults ) where
+
+#include "HsVersions.h"
+
+import HsSyn           ( DefaultDecl(..), LDefaultDecl )
+import Name            ( Name )
+import TcRnMonad
+import TcEnv           ( tcLookupClass )
+import TcHsType                ( tcHsSigType, UserTypeCtxt( DefaultDeclCtxt ) )
+import TcSimplify      ( tcSimplifyDefault )
+import TcType           ( Type, mkClassPred, isTauTy )
+import PrelNames       ( numClassName )
+import SrcLoc          ( Located(..) )
+import Outputable
+\end{code}
+
+\begin{code}
+tcDefaults :: [LDefaultDecl Name]
+          -> TcM (Maybe [Type])    -- Defaulting types to heave
+                                   -- into Tc monad for later use
+                                   -- in Disambig.
+
+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 [L locn (DefaultDecl [])]
+  = returnM (Just [])          -- Default declaration specifying no types
+
+tcDefaults [L locn (DefaultDecl mono_tys)]
+  = setSrcSpan locn                    $
+    addErrCtxt defaultDeclCtxt         $
+    tcLookupClass numClassName         `thenM` \ num_class ->
+    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 (Just tau_tys)
+
+tcDefaults decls@(L locn (DefaultDecl _) : _) =
+    setSrcSpan locn $
+    failWithTc (dupDefaultDeclErr decls)
+
+
+tc_default_ty hs_ty 
+ = tcHsSigType DefaultDeclCtxt hs_ty           `thenM` \ ty ->
+   checkTc (isTauTy ty) (polyDefErr hs_ty)     `thenM_`
+   returnM ty
+
+defaultDeclCtxt =  ptext SLIT("when checking that each type in a default declaration")
+                   $$ ptext SLIT("is an instance of class Num")
+
+
+dupDefaultDeclErr (L _ (DefaultDecl _) : dup_things)
+  = hang (ptext SLIT("Multiple default declarations"))
+      4  (vcat (map pp dup_things))
+  where
+    pp (L locn (DefaultDecl _)) = 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}
+