Re: Getting Rewrite Rules from ModGuts

11 Apr 2019


      Thanks Brandon! Unfortunately, I don't think this is right (or at least it's not sufficient.) If I change the code to use:
    _ <- setSessionDynFlags $ gopt_set flags Opt_EnableRewriteRules
I still read in 0 rewrite rules.

(Unless I'm setting the wrong flag/not enough flags?)

Bill
...
On Apr 11, 2019, at 11:06 PM, Brandon Allbery  wrote:
You might need to enable optimization for RULES to get picked up at all.
On Thu, Apr 11, 2019 at 11:03 PM Bill Hallahan mailto:william.hallahan@yale.edu> wrote:
Hi,
I'm trying to use the GHC API (8.2.2) to extract the rewrite rules from a module, but have run into some difficulties.  I've written the following code (all code is also attached as files):
module Main where
import GHC
    import GHC.Paths
    import HscTypes
main :: IO ()
    main = do
        loadProj "Test.hs"
loadProj :: FilePath -> IO ()
    loadProj src = do
        modgutss <- runGhc (Just libdir) $ do
            flags <- getSessionDynFlags
            _ <- setSessionDynFlags flags
target <- guessTarget src Nothing
            _ <- setTargets [target]
            _ <- load LoadAllTargets
mod_graph <- getModuleGraph
            parsed_mods <- mapM parseModule mod_graph
            typed_mods <- mapM typecheckModule parsed_mods
            desug_mods <- mapM desugarModule typed_mods
return $ map coreModule desug_mods
let rules = map (\mg -> ( moduleNameString . moduleName $ mg_module mg
                                , length $ mg_rules mg)
                        ) modgutss
        print $ rules
return ()
It loads Test.hs (see below my signature) which contains a single rewrite rule.  Then, it obtains the ModGuts, and prints a tuple of the name of the module, and the length of the rule list.  I would expect this to be ("Test", 1), but, in fact, what gets printed is ("Test", 0).  For some reason, the ModGuts does not have the rewrite rule from the file.
I'm guessing I'm misunderstanding something about how the GHC API works.  If anyone has any advice about how to fix this code to load rewrite rules (or even where to begin looking) I would appreciate it!
Thanks,
Bill Hallahan
Test.hs:
    module Test where
import Prelude hiding (map)
map :: (a -> b) -> [a] -> [b]
    map f (x:xs) = f x:map f xs
    map _ [] = []
    {-# NOINLINE [0] map #-}
{-# RULES
     "map/map"   forall f g xs . map f (map g xs) = map (f . g) xs
      #-}
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-- 
brandon s allbery kf8nh
allbery.b@gmail.com mailto:allbery.b@gmail.com