Defining lenses and prisms without depending on lens.

lensnprism.hs

streams :: forall f. Functor f => ((StdStream,StdStream,StdStream) -> f (StdStream,StdStream,StdStream)) -> CreateProcess -> f CreateProcess 
streams f c = setStreams c <$> f (getStreams c)
    where 
    getStreams c = (std_in c,std_out c, std_err c)
    setStreams c (s1,s2,s3) = c { std_in  = s1 
                                , std_out = s2 
                                , std_err = s3 
                                } 

pipe3 :: (StdStream,StdStream,StdStream)
pipe3 = (CreatePipe,CreatePipe,CreatePipe)

handle3 :: forall m. Applicative m => ((Handle, Handle, Handle, ProcessHandle) -> m (Handle, Handle, Handle, ProcessHandle)) -> (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle) -> m (Maybe Handle, Maybe Handle, Maybe Handle, ProcessHandle)
handle3 f quad = case impure quad of
    Left l -> pure l
    Right r -> fmap justify (f r)
    where    
    impure (Just h1, Just h2, Just h3, phandle) = Right (h1, h2, h3, phandle) 
    impure x = Left x
    justify (h1, h2, h3, phandle) = (Just h1, Just h2, Just h3, phandle)