Fix an nasty black hole, concerning computation of isRecursiveTyCon

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

diff --git a/compiler/typecheck/TcTyDecls.lhs b/compiler/typecheck/TcTyDecls.lhs
index 8b9c6f1..9b0e681 100644 (file)
--- a/compiler/typecheck/TcTyDecls.lhs
+++ b/compiler/typecheck/TcTyDecls.lhs
@@ -9,13 +9,6 @@ This stuff is only used for source-code decls; it's recorded in interface
 files for imported data types.
 
 \begin{code}
-{-# OPTIONS -w #-}
--- The above warning supression flag is a temporary kludge.
--- While working on this module you are encouraged to remove it and fix
--- any warnings in the module. See
---     http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
--- for details
-
 module TcTyDecls(
         calcRecFlags,
         calcClassCycles, calcSynCycles
@@ -38,6 +31,8 @@ import Digraph
 import BasicTypes
 import SrcLoc
 import Outputable
+import Util ( isSingleton )
+import List ( partition )
 \end{code}
 
 
@@ -109,7 +104,7 @@ synTyConsOfType ty
 \begin{code}
 calcSynCycles :: [LTyClDecl Name] -> [SCC (LTyClDecl Name)]
 calcSynCycles decls
-  = stronglyConnComp syn_edges
+  = stronglyConnCompFromEdgedVertices syn_edges
   where
     syn_edges = [ (ldecl, unLoc (tcdLName decl),
                           mk_syn_edges (tcdSynRhs decl))
@@ -121,7 +116,7 @@ calcSynCycles decls
 
 calcClassCycles :: [LTyClDecl Name] -> [[LTyClDecl Name]]
 calcClassCycles decls
-  = [decls | CyclicSCC decls <- stronglyConnComp cls_edges]
+  = [decls | CyclicSCC decls <- stronglyConnCompFromEdgedVertices cls_edges]
   where
     cls_edges = [ (ldecl, unLoc (tcdLName decl),
                           mk_cls_edges (unLoc (tcdCtxt decl)))
@@ -239,9 +234,18 @@ calcRecFlags boot_details tyclss
         -- loop.  We could program round this, but it'd make the code
         -- rather less nice, so I'm not going to do that yet.
 
+    single_con_tycons = filter (isSingleton . tyConDataCons) all_tycons
+        -- Both newtypes and data types, with exactly one data constructor
+    (new_tycons, prod_tycons) = partition isNewTyCon single_con_tycons
+        -- NB: we do *not* call isProductTyCon because that checks
+       --     for vanilla-ness of data constructors; and that depends
+       --     on empty existential type variables; and that is figured
+       --     out by tcResultType; which uses tcMatchTy; which uses
+       --     coreView; which calls coreExpandTyCon_maybe; which uses
+       --     the recursiveness of the TyCon.  Result... a black hole.
+       -- YUK YUK YUK
+
         --------------- Newtypes ----------------------
-    new_tycons = filter isNewTyConAndNotOpen all_tycons
-    isNewTyConAndNotOpen tycon = isNewTyCon tycon && not (isOpenTyCon tycon)
     nt_loop_breakers = mkNameSet (findLoopBreakers nt_edges)
     is_rec_nt tc = tyConName tc  `elemNameSet` nt_loop_breakers
         -- is_rec_nt is a locally-used helper function
@@ -252,16 +256,13 @@ calcRecFlags boot_details tyclss
         = concatMap (mk_nt_edges1 nt) (tcTyConsOfType (new_tc_rhs nt))
                         -- tyConsOfType looks through synonyms
 
-    mk_nt_edges1 nt tc
+    mk_nt_edges1 _ tc
         | tc `elem` new_tycons = [tc]           -- Loop
                 -- At this point we know that either it's a local *data* type,
                 -- or it's imported.  Either way, it can't form part of a newtype cycle
         | otherwise = []
 
         --------------- Product types ----------------------
-        -- The "prod_tycons" are the non-newtype products
-    prod_tycons = [tc | tc <- all_tycons,
-                        not (isNewTyCon tc), isProductTyCon tc]
     prod_loop_breakers = mkNameSet (findLoopBreakers prod_edges)
 
     prod_edges = [(tc, mk_prod_edges tc) | tc <- prod_tycons]
@@ -280,11 +281,13 @@ calcRecFlags boot_details tyclss
                 -- or it's imported.  Either way, it can't form part of a cycle
         | otherwise = []
 
+new_tc_rhs :: TyCon -> Type
 new_tc_rhs tc = snd (newTyConRhs tc)    -- Ignore the type variables
 
+getTyCon :: TyThing -> TyCon
 getTyCon (ATyCon tc) = tc
 getTyCon (AClass cl) = classTyCon cl
-getTyCon other       = panic "getTyCon"
+getTyCon _           = panic "getTyCon"
 
 findLoopBreakers :: [(TyCon, [TyCon])] -> [Name]
 -- Finds a set of tycons that cut all loops
@@ -292,7 +295,7 @@ findLoopBreakers deps
   = go [(tc,tc,ds) | (tc,ds) <- deps]
   where
     go edges = [ name
-               | CyclicSCC ((tc,_,_) : edges') <- stronglyConnCompR edges,
+               | CyclicSCC ((tc,_,_) : edges') <- stronglyConnCompFromEdgedVerticesR edges,
                  name <- tyConName tc : go edges']
 \end{code}
 
@@ -310,14 +313,14 @@ tcTyConsOfType ty
   where
      go :: Type -> NameEnv TyCon  -- The NameEnv does duplicate elim
      go ty | Just ty' <- tcView ty = go ty'
-     go (TyVarTy v)                = emptyNameEnv
+     go (TyVarTy _)                = emptyNameEnv
      go (TyConApp tc tys)          = go_tc tc tys
      go (AppTy a b)                = go a `plusNameEnv` go b
      go (FunTy a b)                = go a `plusNameEnv` go b
      go (PredTy (IParam _ ty))     = go ty
      go (PredTy (ClassP cls tys))  = go_tc (classTyCon cls) tys
      go (ForAllTy _ ty)            = go ty
-     go other                      = panic "tcTyConsOfType"
+     go _                          = panic "tcTyConsOfType"
 
      go_tc tc tys = extendNameEnv (go_s tys) (tyConName tc) tc
      go_s tys = foldr (plusNameEnv . go) emptyNameEnv tys