an erlang monad?
Wed Mar 2 21:15:06 CET 2005
Den 2005-03-02 18:25:47 skrev Matthias Kretschmer <>:
> This is something I use monads for, too. Hiding some sort of state or
> other information (serialization of operation or doing i/o is not that
> much of a concern using Erlang :-)). I wrote a little parse_transform'er
> to make the notation easier:
> 1 = mreturn(1),
> X = Action3,
> this would be roughly like (assuming MT.>>= is an infix operation):
> Action0 MT.>>= fun (_) ->
> Action1 MT.>>= fun (_) ->
> MT.return(1) MT.>>= fun (1) ->
> Action2 MT.>>= fun (_) ->
> Action3 MT.>>= fun (X) ->
> Action4 MT.>>= fun (_) ->
> Action5(X) end end end end end
> trying to resemble basically Haskell's do-notation -- except that
> instead of "X <- Action" "X = Action" (the MT is the monad type
> specification -- basically a tuple containing the "bind"/">>=",
> "return", etc. functions).
Great! Couple this with John Hughes' ?DELAY and ?FORCE macros,
and you've almost got yourself a real language (except for the
lack of static typing, of course) ;-)
> This way you may even drop the fun (D) -> ... end and just write the
> expressions, using appropriate monad values for reading and writing the
> state (e.g. wrapping the basic dictionary operations).
I played around for a while with macros in order to avoid
having to write fun(D) -> ... end all the time, but eventually
I gave up.
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