[Caml-list] Monadic classes

["Christoph Höger" <christoph.hoeger@tu-berlin.de>]

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Dear all,

suppose, you have a state monad, i.e. a simple int counter:

let next s = (s+1, s) ;;

and now you want to make use of that state monad during class
construction:

class a s = let (s', _x) = next s in
            let (s'', _y) = next s' in
            object method x = _x ; method y = _y end ;;

class b s = let (s', _z) = next s in
            object method z = _z end ;;

What you can do, is single inheritance:

class c s = object inherit a s end ;;

(new c 2)#y ;; (* evaluates to: - : int = 3 *)


But to have a truly monadic class construction, I would have to
_return_ the state from the instantiated class and pass it on to the
second class, i.e. something like this:

class c s = object s' = inherit a s ; inherit b s' end ;;

Is something like this possible in OCaml?

regards,

Christoph

- -- 
Christoph Höger

Technische Universität Berlin
Fakultät IV - Elektrotechnik und Informatik
Übersetzerbau und Programmiersprachen

Sekr. TEL12-2, Ernst-Reuter-Platz 7, 10587 Berlin

Tel.: +49 (30) 314-24890
E-Mail: christoph.hoeger@tu-berlin.de
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