[project @ 2004-01-05 09:35:39 by simonpj]

Buglet in desugaring instance declarations

diff --git a/ghc/compiler/deSugar/DsMeta.hs b/ghc/compiler/deSugar/DsMeta.hs
index 31a8a0d..4bcb32e 100644 (file)
--- a/ghc/compiler/deSugar/DsMeta.hs
+++ b/ghc/compiler/deSugar/DsMeta.hs
@@ -213,20 +213,24 @@ repTyClD (L loc d) = do { dsWarn (loc, hang msg 4 (ppr d)) ;
   where
     msg = ptext SLIT("Cannot desugar this Template Haskell declaration:")
 
-repInstD' (L loc (InstDecl ty binds _))
-       -- Ignore user pragmas for now
- = do  { cxt1 <- repContext cxt
-       ; inst_ty1 <- repPred (HsClassP cls tys)
-       ; ss <- mkGenSyms (collectHsBindBinders binds)
-       ; binds1 <- addBinds ss (rep_binds binds)
-       ; decls1 <- coreList decQTyConName binds1
-       ; decls2 <- wrapNongenSyms ss decls1
-               -- wrapNonGenSyms: do not clone the class op names!
-               -- They must be called 'op' etc, not 'op34'
-       ; i <- repInst cxt1 inst_ty1 decls2
+repInstD' (L loc (InstDecl ty binds _))                -- Ignore user pragmas for now
+ = do  { i <- addTyVarBinds tvs $ \tv_bndrs ->
+               -- We must bring the type variables into scope, so their occurrences
+               -- don't fail,  even though the binders don't appear in the resulting 
+               -- data structure
+               do {  cxt1 <- repContext cxt
+                  ; inst_ty1 <- repPred (HsClassP cls tys)
+                  ; ss <- mkGenSyms (collectHsBindBinders binds)
+                  ; binds1 <- addBinds ss (rep_binds binds)
+                  ; decls1 <- coreList decQTyConName binds1
+                  ; decls2 <- wrapNongenSyms ss decls1
+                  -- wrapNonGenSyms: do not clone the class op names!
+                  -- They must be called 'op' etc, not 'op34'
+                  ; repInst cxt1 inst_ty1 decls2 }
+
        ; return (loc, i)}
  where
-   (_, cxt, cls, tys) = splitHsInstDeclTy (unLoc ty)
+   (tvs, cxt, cls, tys) = splitHsInstDeclTy (unLoc ty)
 
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 --                     Constructors