Re: [Caml-list] composing functions...

[Pietro Abate <Pietro.Abate@anu.edu.au>]

Let's see if I'm able to apply these 4 days of reading about monads...

module ListMonadMake(T:sig type t end) =
struct
    type mt = T.t list
    let return x = [x]
    let join mm = List.flatten mm
    let map f m = List.map f m
    let bind m f = join (map f m)
    let mzero = []
    let mplus = List.append
end

module LM = ListMonadMake(struct type t = int end);;
open LM ;;

let apply1 (a,b,c) = [a;b;int_of_char c] ;;
let apply2 a = [a] ;;

let compose f1 f2 m = bind (bind (return m) f2) f1;;
let f v = compose apply1 apply2 v ;;
f (1,2,'a');;
- : int list = [1; 2; 97]

does this help ? I'm still learning, but I see a lot of potential
here... How do people encode monads in ocaml ? Can you use objects
to build monads similarly to Haskell ?

:)
pp

On Thu, Dec 01, 2005 at 01:55:38PM +1300, Jonathan Roewen wrote:
> Hi,
> 
> I'm getting a bit stuck, and am wondering if there's anyway to compose
> a bunch of functions together easily without having to pre-maturely
> apply any of them.
> 
> My current idea is trying to use objects, like:
> 
> class virtual ['a] composable = object (self)
>   method compose a b = self#apply a @ b
>   method virtual apply : 'a -> int list
> end;;
> 
> class c1 = object
>   inherit ['a] composable
>   method apply (a,b,c) -> [a;b;int_of_char c]
> end;;
> 
> class c2 = object
>   inherit ['a] composable
>   method apply a -> [a]
> end;;
> 
> let o1 = new c1 and o2 = new c2;;
> 
> I can do something like let f a1 a2 = o1#compose a1 (o2#compose a2
> []);; and get a list back...
> 
> But what I'm wondering is if it's possible to make a generic compose
> function that takes say a list of either classes or object instances,
> and return a new function that I can apply the bunch of tuples to.
> 
> Theory: let f = compose [o1;o2];; f a1 a2;; maybe it's not worth the
> hassle (if it's even possible).
> 
> Jonathan
> 
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