Re: [Ocaml-lib-devel] [Batteries] First patch: Option, LazyList

[blue s. <blu...@gm...>]

On 5/21/08, David Teller <Dav...@un...> wrote:
> What should it do if there is more than one element in the enumeration ?
> Raise an error or just consume the first element ?

If think consuming the first element only is the saner decision. It's
the strategy used by monadic sums, and the C-ish bool_of_int
translation (0 -> false,  everythin else -> true, so there is an
information loss). Besides, it totally makes sense (when you think of
option as a failure/success representation) that Option.of_enum
(Enum.filter ...) behaves roughly as an Enum.find.


> If we have to write a bind, I'd keep it consistent with other
> OCaml-based binds, i.e. in the same order as Haskell.

And it's the order that pa_monad use. Agreed.
Below is a new patch with the usual parameters order.

Against option.mli :
32a33,35
> val bind : 'a option -> ('a -> 'b option) -> 'b option
> (** [bind None f] returns [None] and [bind (Some x) f] returns [f x] *)
>

Against option.ml :
26a27,30
> let bind opt f = match opt with
>         | None -> None
>         | Some v -> f v
>

Quick usage test :
# let may_sum a b = Option.bind a (fun a_val -> Option.bind b (fun
b_val -> Some (a_val + b_val)));;
val may_sum : int option -> int option -> int option = <fun>
# may_sum (Some 1) (Some 2), may_sum (Some 2) None;;
- : int option * int option = (Some 3, None)