Chris Kuklewicz wrote:
Brian Hulley wrote:
Hi, I'm designing an API for a simple graphics window, and am trying to [snip]
There should be no overhead for a newtype. The above can be shortened to one line:
newtype VertexM a = VertexM (IO a) deriving (Functor,Monad,MonadIO)
Thanks - that certainly saves a lot of typing! :-)
(Needs ghc -fglasgow-exts, I expect)
Also, in:
foreign import ccall duma_vertex3f :: Float -> Float -> Float -> IO ()
vertex3f :: Float -> Float -> Float -> VertexM () vertex3f x y z = liftIO $ duma_vertex3f x y z
is there a penalty involved in calling vertex3f (from another module) or will the worker/wrapper optimization ensure that machine code in the other module just calls duma_vertex3f directly since the liftIO operation is just an irrelevance at the machine code level?
I doubt there is a penalty. [snip] In particular -ddump-simpl has been helpful for some people, and you want -ddump-stg, perhaps.
I've just now tried compiling with -ddump-stg but this is difficult (for me) to understand so I tried with -ddump-simpl as you suggested, and compared the outputs when compiling with and without the -O2 optimization flag. With -O2 enabled, __ccall_GC duma_vertex3f is indeed called directly instead of vertex3f, from a different module, so that proves that different monads can indeed be used to wrap IO operations without any performance penalty at all. What a great language and compiler!!! :-) One little thing I wondered about when looking at the -ddump-simpl output: for each C API function, there is a warning of the form: warning: implicit declaration of function `duma_vertex3f' Do you know what this means? It doesn't seem to matter as everything compiles and runs ok but it would be interesting to know. Thanks, Brian.