X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FhsSyn%2FHsExpr.lhs;h=78577072efb9c8982082bbf2bc79af73ea513727;hb=edc0bafd3fcd01b85a2e8894e5dfe149eb0e0857;hp=245631d789680d8cf873d97b567f66db29e32afe;hpb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516;p=ghc-hetmet.git

diff --git a/compiler/hsSyn/HsExpr.lhs b/compiler/hsSyn/HsExpr.lhs
index 245631d..7857707 100644
--- a/compiler/hsSyn/HsExpr.lhs
+++ b/compiler/hsSyn/HsExpr.lhs
@@ -132,7 +132,10 @@ data HsExpr id
   | HsCase      (LHsExpr id)
                 (MatchGroup id)
 
-  | HsIf        (LHsExpr id)    --  predicate
+  | HsIf        (Maybe (SyntaxExpr id)) -- cond function
+    		       		        -- Nothing => use the built-in 'if'
+					-- See Note [Rebindable if]
+                (LHsExpr id)    --  predicate
                 (LHsExpr id)    --  then part
                 (LHsExpr id)    --  else part
 
@@ -297,11 +300,18 @@ type PendingSplice = (Name, LHsExpr Id) -- Typechecked splices, waiting to be
                                         -- pasted back in by the desugarer
 \end{code}
 
-A @Dictionary@, unless of length 0 or 1, becomes a tuple.  A
-@ClassDictLam dictvars methods expr@ is, therefore:
-\begin{verbatim}
-\ x -> case x of ( dictvars-and-methods-tuple ) -> expr
-\end{verbatim}
+Note [Rebindable if]
+~~~~~~~~~~~~~~~~~~~~
+The rebindable syntax for 'if' is a bit special, because when
+rebindable syntax is *off* we do not want to treat
+   (if c then t else e)
+as if it was an application (ifThenElse c t e).  Why not?
+Because we allow an 'if' to return *unboxed* results, thus 
+  if blah then 3# else 4#
+whereas that would not be possible using a all to a polymorphic function
+(because you can't call a polymorphic function at an unboxed type).
+
+So we use Nothing to mean "use the old built-in typing rule".
 
 \begin{code}
 instance OutputableBndr id => Outputable (HsExpr id) where
@@ -414,7 +424,7 @@ ppr_expr exprType@(HsCase expr matches)
           nest 2 (pprMatches (CaseAlt `asTypeOf` idType exprType) matches <+> char '}') ]
  where idType :: HsExpr id -> HsMatchContext id; idType = undefined
 
-ppr_expr (HsIf e1 e2 e3)
+ppr_expr (HsIf _ e1 e2 e3)
   = sep [hsep [ptext (sLit "if"), nest 2 (ppr e1), ptext (sLit "then")],
          nest 4 (ppr e2),
          ptext (sLit "else"),
@@ -619,7 +629,8 @@ The legal constructors for commands are:
                 [Match id]      -- bodies are HsCmd's
                 SrcLoc
 
-  | HsIf        (HsExpr id)     --  predicate
+  | HsIf        (Maybe (SyntaxExpr id)) --  cond function
+  					 (HsExpr id)     --  predicate
                 (HsCmd id)      --  then part
                 (HsCmd id)      --  else part
                 SrcLoc
@@ -748,16 +759,16 @@ pprFunBind fun inf matches = pprMatches (FunRhs fun inf) matches
 pprPatBind :: (OutputableBndr bndr, OutputableBndr id)
            => LPat bndr -> GRHSs id -> SDoc
 pprPatBind pat ty@(grhss)
- = sep [ppr pat, nest 4 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
+ = sep [ppr pat, nest 2 (pprGRHSs (PatBindRhs `asTypeOf` idType ty) grhss)]
 --avoid using PatternSignatures for stage1 code portability
  where idType :: GRHSs id -> HsMatchContext id; idType = undefined
 
 
 pprMatch :: (OutputableBndr idL, OutputableBndr idR) => HsMatchContext idL -> Match idR -> SDoc
 pprMatch ctxt (Match pats maybe_ty grhss)
-  = herald <+> sep [sep (map pprParendLPat other_pats),
-                    ppr_maybe_ty,
-                    nest 2 (pprGRHSs ctxt grhss)]
+  = sep [ sep (herald : map (nest 2 . pprParendLPat) other_pats)
+        , nest 2 ppr_maybe_ty
+        , nest 2 (pprGRHSs ctxt grhss) ]
   where
     (herald, other_pats)
         = case ctxt of
@@ -997,8 +1008,8 @@ pprStmt (ExprStmt expr _ _)       = ppr expr
 pprStmt (ParStmt stmtss)          = hsep (map doStmts stmtss)
   where doStmts stmts = ptext (sLit "| ") <> ppr stmts
 
-pprStmt (TransformStmt stmts _ using by)
-  = sep (ppr_lc_stmts stmts ++ [pprTransformStmt using by])
+pprStmt (TransformStmt stmts bndrs using by)
+  = sep (ppr_lc_stmts stmts ++ [pprTransformStmt bndrs using by])
 
 pprStmt (GroupStmt stmts _ by using) 
   = sep (ppr_lc_stmts stmts ++ [pprGroupStmt by using])
@@ -1010,8 +1021,11 @@ pprStmt (RecStmt { recS_stmts = segment, recS_rec_ids = rec_ids
          , ifPprDebug (vcat [ ptext (sLit "rec_ids=") <> ppr rec_ids
                             , ptext (sLit "later_ids=") <> ppr later_ids])]
 
-pprTransformStmt :: OutputableBndr id => LHsExpr id -> Maybe (LHsExpr id) -> SDoc
-pprTransformStmt using by = sep [ ptext (sLit "then"), nest 2 (ppr using), nest 2 (pprBy by)]
+pprTransformStmt :: OutputableBndr id => [id] -> LHsExpr id -> Maybe (LHsExpr id) -> SDoc
+pprTransformStmt bndrs using by
+  = sep [ ptext (sLit "then") <+> ifPprDebug (braces (ppr bndrs))
+        , nest 2 (ppr using)
+        , nest 2 (pprBy by)]
 
 pprGroupStmt :: OutputableBndr id => Maybe (LHsExpr id)
                                   -> Either (LHsExpr id) (SyntaxExpr is)
@@ -1277,7 +1291,7 @@ pprStmtInCtxt ctxt stmt = hang (ptext (sLit "In a stmt of") <+> pprStmtContext c
 		    	  4 (ppr_stmt stmt)
   where
     -- For Group and Transform Stmts, don't print the nested stmts!
-    ppr_stmt (GroupStmt _ _ by using)     = pprGroupStmt by using
-    ppr_stmt (TransformStmt _ _ using by) = pprTransformStmt using by
-    ppr_stmt stmt                         = pprStmt stmt
+    ppr_stmt (GroupStmt _ _ by using)         = pprGroupStmt by using
+    ppr_stmt (TransformStmt _ bndrs using by) = pprTransformStmt bndrs using by
+    ppr_stmt stmt                             = pprStmt stmt
 \end{code}