[project @ 2002-03-18 15:21:59 by simonpj]

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

diff --git a/ghc/compiler/typecheck/TcDeriv.lhs b/ghc/compiler/typecheck/TcDeriv.lhs
index de7b2b3..da56ca9 100644 (file)
--- a/ghc/compiler/typecheck/TcDeriv.lhs
+++ b/ghc/compiler/typecheck/TcDeriv.lhs
@@ -14,11 +14,11 @@ import HsSyn                ( HsBinds(..), MonoBinds(..), TyClDecl(..),
                          collectLocatedMonoBinders )
 import RdrHsSyn                ( RdrNameMonoBinds )
 import RnHsSyn         ( RenamedHsBinds, RenamedMonoBinds, RenamedTyClDecl, RenamedHsPred )
-import CmdLineOpts     ( DynFlag(..), DynFlags )
+import CmdLineOpts     ( DynFlag(..) )
 
 import TcMonad
 import TcEnv           ( tcSetInstEnv, newDFunName, InstInfo(..), pprInstInfo,
-                         tcLookupClass, tcLookupTyCon, tcExtendTyVarEnv
+                         tcLookupTyCon, tcExtendTyVarEnv
                        )
 import TcGenDeriv      -- Deriv stuff
 import InstEnv         ( InstEnv, simpleDFunClassTyCon, extendInstEnv )
@@ -28,11 +28,11 @@ import TcSimplify   ( tcSimplifyDeriv )
 import RnBinds         ( rnMethodBinds, rnTopMonoBinds )
 import RnEnv           ( bindLocatedLocalsRn )
 import RnMonad         ( renameDerivedCode, thenRn, mapRn, returnRn )
-import HscTypes                ( DFunId, PersistentRenamerState )
+import HscTypes                ( DFunId, PersistentRenamerState, FixityEnv )
 
-import BasicTypes      ( Fixity, NewOrData(..) )
+import BasicTypes      ( NewOrData(..) )
 import Class           ( className, classKey, classTyVars, Class )
-import ErrUtils                ( dumpIfSet_dyn, Message )
+import ErrUtils                ( dumpIfSet_dyn )
 import MkId            ( mkDictFunId )
 import DataCon         ( dataConRepArgTys, isNullaryDataCon, isExistentialDataCon )
 import PrelInfo                ( needsDataDeclCtxtClassKeys )
@@ -47,15 +47,14 @@ import TyCon                ( tyConTyVars, tyConDataCons, tyConArity, newTyConRep,
                        )
 import TcType          ( TcType, ThetaType, mkTyVarTys, mkTyConApp, getClassPredTys_maybe,
                          isUnLiftedType, mkClassPred, tyVarsOfTypes, tcSplitFunTys, 
-                         tcSplitTyConApp_maybe, tcEqTypes, tyVarsOfTheta )
+                         tcSplitTyConApp_maybe, tcEqTypes )
 import Var             ( TyVar, tyVarKind )
 import VarSet          ( mkVarSet, subVarSet )
 import PrelNames
-import Util            ( zipWithEqual, sortLt, eqListBy )
+import Util            ( zipWithEqual, sortLt )
 import ListSetOps      ( removeDups,  assoc )
 import Outputable
 import Maybe           ( isJust )
-import List            ( nub )
 import FastString      ( FastString )
 \end{code}
 
@@ -148,6 +147,9 @@ type DerivEqn = (Name, Class, TyCon, [TyVar], DerivRhs)
                -- The Name is the name for the DFun we'll build
                -- The tyvars bind all the variables in the RHS
 
+pprDerivEqn (n,c,tc,tvs,rhs)
+  = parens (hsep [ppr n, ppr c, ppr tc, ppr tvs] <+> equals <+> ppr rhs)
+
 type DerivRhs  = ThetaType
 type DerivSoln = DerivRhs
 \end{code}
@@ -187,7 +189,7 @@ context to the instance decl.  The "offending classes" are
 tcDeriving  :: PersistentRenamerState
            -> Module                   -- name of module under scrutiny
            -> InstEnv                  -- What we already know about instances
-           -> (Name -> Maybe Fixity)   -- used in deriving Show and Read
+           -> FixityEnv        -- used in deriving Show and Read
            -> [RenamedTyClDecl]        -- All type constructors
            -> TcM ([InstInfo],         -- The generated "instance decls".
                    RenamedHsBinds)     -- Extra generated bindings
@@ -486,7 +488,7 @@ solveDerivEqns :: InstEnv
                                -- This bunch is Absolutely minimal...
 
 solveDerivEqns inst_env_in orig_eqns
-  = iterateDeriv initial_solutions
+  = iterateDeriv 1 initial_solutions
   where
        -- The initial solutions for the equations claim that each
        -- instance has an empty context; this solution is certainly
@@ -499,8 +501,14 @@ solveDerivEqns inst_env_in orig_eqns
        -- compares it with the current one; finishes if they are the
        -- same, otherwise recurses with the new solutions.
        -- It fails if any iteration fails
-    iterateDeriv :: [DerivSoln] ->TcM [DFunId]
-    iterateDeriv current_solns
+    iterateDeriv :: Int -> [DerivSoln] ->TcM [DFunId]
+    iterateDeriv n current_solns
+      | n > 20         -- Looks as if we are in an infinite loop
+               -- This can happen if we have -fallow-undecidable-instances
+               -- (See TcSimplify.tcSimplifyDeriv.)
+      = pprPanic "solveDerivEqns: probable loop" 
+                (vcat (map pprDerivEqn orig_eqns) $$ ppr current_solns)
+      | otherwise
       =        getDOptsTc                              `thenNF_Tc` \ dflags ->
         let 
            dfuns    = zipWithEqual "add_solns" mk_deriv_dfun orig_eqns current_solns
@@ -515,7 +523,7 @@ solveDerivEqns inst_env_in orig_eqns
        if (current_solns == new_solns) then
            returnTc dfuns
        else
-           iterateDeriv new_solns
+           iterateDeriv (n+1) new_solns
 
     ------------------------------------------------------------------
 
@@ -607,7 +615,7 @@ the renamer.  What a great hack!
 -- Generate the method bindings for the required instance
 -- (paired with class name, as we need that when renaming
 --  the method binds)
-gen_bind :: (Name -> Maybe Fixity) -> DFunId -> (Name, RdrNameMonoBinds)
+gen_bind :: FixityEnv -> DFunId -> (Name, RdrNameMonoBinds)
 gen_bind get_fixity dfun
   = (cls_nm, binds)
   where