make head/build rule apply to all types, not just Bool.

diff --git a/GHC/List.lhs b/GHC/List.lhs
index 0d43453..705fdc9 100644 (file)
--- a/GHC/List.lhs
+++ b/GHC/List.lhs
@@ -63,7 +63,7 @@ badHead = errorEmptyList "head"
 -- This rule is useful in cases like 
 --     head [y | (x,y) <- ps, x==t]
 {-# RULES
-"head/build"   forall (g::forall b.(Bool->b->b)->b->b) . 
+"head/build"   forall (g::forall b.(a->b->b)->b->b) .
                head (build g) = g (\x _ -> x) badHead
 "head/augment" forall xs (g::forall b. (a->b->b) -> b -> b) . 
                head (augment g xs) = g (\x _ -> x) (head xs)