Getting Rewrite Rules from ModGuts

[Roland Senn]

Hi Bill,

You may try to set the DynFlag Opt_IgnoreInterfacePragmas to False.
If set to True,, which is the default, GHC doesn't load a lot of
optimization stuff.
Good luck and kind regards

Roland

Am Donnerstag, den 11.04.2019, 23:02 -0400 schrieb Bill Hallahan:
> 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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