[project @ 2005-08-12 08:10:50 by simonmar]

[ghc-hetmet.git] / ghc / compiler / coreSyn / CoreUtils.lhs

diff --git a/ghc/compiler/coreSyn/CoreUtils.lhs b/ghc/compiler/coreSyn/CoreUtils.lhs
index 53761d5..a8c7eae 100644 (file)
--- a/ghc/compiler/coreSyn/CoreUtils.lhs
+++ b/ghc/compiler/coreSyn/CoreUtils.lhs
@@ -450,17 +450,20 @@ idAppIsCheap id n_val_args
   | n_val_args == 0 = True     -- Just a type application of
                                -- a variable (f t1 t2 t3)
                                -- counts as WHNF
-  | otherwise = case globalIdDetails id of
-                 DataConWorkId _ -> True                       
-                 RecordSelId _ _ -> True       -- I'm experimenting with making record selection
-                 ClassOpId _     -> True       -- look cheap, so we will substitute it inside a
-                                               -- lambda.  Particularly for dictionary field selection
-
-                 PrimOpId op   -> primOpIsCheap op     -- In principle we should worry about primops
-                                                       -- that return a type variable, since the result
-                                                       -- might be applied to something, but I'm not going
-                                                       -- to bother to check the number of args
-                 other       -> n_val_args < idArity id
+  | otherwise 
+  = case globalIdDetails id of
+       DataConWorkId _ -> True
+       RecordSelId _ _ -> n_val_args == 1      -- I'm experimenting with making record selection
+       ClassOpId _     -> n_val_args == 1      -- look cheap, so we will substitute it inside a
+                                               -- lambda.  Particularly for dictionary field selection.
+               -- BUT: Take care with (sel d x)!  The (sel d) might be cheap, but
+               --      there's no guarantee that (sel d x) will be too.  Hence (n_val_args == 1)
+
+       PrimOpId op   -> primOpIsCheap op       -- In principle we should worry about primops
+                                               -- that return a type variable, since the result
+                                               -- might be applied to something, but I'm not going
+                                               -- to bother to check the number of args
+       other         -> n_val_args < idArity id
 \end{code}
 
 exprOkForSpeculation returns True of an expression that it is