On 16 March 2015 at 19:51, Maurizio Vitale
suppose I have a restricted IO monad, RIO that only exposes readFile. and then I have a monad SIO that will eventually provide a virtual file system from a map path->content, also with a readFile function returning SIO(String).
What is the way to write a function parseFile that can operate in both monads so that I can use SIO for testing? should I define a third monad CompileMonad that has instances for both RIO and SIO and then having parseFile :: CompileMonad ast?
You might be able to do something like, class MonadIO m => ProvidesReadFile m where readFile :: FilePath -> m String instance ProvidesReadFile RIO where readFile = readFileRIO -- the RIO specific readFile instance ProvidesReadFile SIO where readFile = readFileSIO -- the SIO specific readFile parseFile :: ProvidesReadFile m => FilePath -> m ast parseFile = do f <- readFile let ast = parse f -- the pure parser return ast -- works for both monads
Thanks,
Maurizio
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This is more suitable for the haskell-cafe. I am posting it there so that more people might comment on it. HTH. -- Regards Sumit Sahrawat