On Thu, May 5, 2011 at 10:36 AM, Scott Kilpatrick wrote:

I'm looking for "real" code that uses the kind of GHC rewrite rule that specializes a polymorphic function with another one, as described here <http://www.haskell.org/ghc/docs/latest/html/users_guide/rewrite- rules.html#rule-spec>.  Can anyone point me to any popular packages in Hackage that make use of this?

I can't or rather won't go so far as point out specific Hackage packages. What I can give you is the output of grepping my 111k corpus, which resulted in 744 hits for RULES. Attached is the output of `find ~/bin -name "*.lhs" -exec grep -l "{-# RULES " {} \; -exec grep --after-context=3 "{-# RULES " {} \;`. Sample output: /home/gwern/bin/jaspervdj/blaze-builder/benchmarks/LazyByteString.hs {-# RULES "fromWriteReplicated/writeWord8" fromWriteReplicated writeWord8 = fromReplicateWord8 #-} /home/gwern/bin/bloomfilter/Data/BloomFilter.hs {-# RULES "Bloom insertB . insertB" forall a b u. insertB b (insertB a u) = insertListB [a,b] u #-} {-# RULES "Bloom insertListB . insertB" forall x xs u. insertListB xs (insertB x u) = insertListB (x:xs) u #-} {-# RULES "Bloom insertB . insertListB" forall x xs u. insertB x (insertListB xs u) = insertListB (x:xs) u #-} {-# RULES "Bloom insertListB . insertListB" forall xs ys u. insertListB xs (insertListB ys u) = insertListB (xs++ys) u #-} {-# RULES "Bloom insertListB . emptyB" forall h n xs. insertListB xs (emptyB h n) = fromListB h n xs #-} {-# RULES "Bloom insertListB . singletonB" forall h n x xs. insertListB xs (singletonB h n x) = fromListB h n (x:xs) #-} /home/gwern/bin/batterseapower/haskell-kata/DeforestFree.hs {-# RULES "reify/interpret" forall xs. interpret (reify xs) = xs #-} /home/gwern/bin/altaic/testsuite/tests/ghc-regress/simplCore/should_run/simplrun002.hs {-# RULES "foo" forall v . fst (sndSnd v) = trace "Yes" (fst v) #-} main :: IO () main = print (fst (sndSnd (True, (False,True)))) -- gwern http://www.gwern.net