The only solution I can come up with is to convert the array to a list
and then pattern-match like so:
match (Array.to_list [|1;2;3|]) with
x :: [] -> x
|[] -> -1

But this doesn't seem particularly efficient or elegant.

-deech

--- In ocaml_beginners <at> yahoogroups.com, "deech_99" <deech_99 <at> ...> wrote:
>
> Ocaml offers pattern matching on arrays, but it doesn't seem to behave
> like list pattern-matching.
>
> For instance, the following, where 'x' is the first element and '_' is
> the rest of the array doesn't work:
> # match [|1;2;3|] with [|x;_|] -> x;;
>
> Characters 0-33:
>
> match [|1;2;3|] with [|x;_|] -> x;;
>
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Warning P: this pattern-matching is not exhaustive.
>
> Here is an example of a value that is not matched:
>
> [| |]
>
> Exception: Match_failure ("", 100, -408).
>
> Is there some way to do this in Ocaml?
> -deech
>

•  1
  New Members

On Mon, Dec 01, 2008 at 12:33:31AM -0000, deech_99 wrote:
> Ocaml offers pattern matching on arrays, but it doesn't seem to behave
> like list pattern-matching.
>
> For instance, the following, where 'x' is the first element and '_' is
> the rest of the array doesn't work:
> # match [|1;2;3|] with [|x;_|] -> x;;

You can't do what you want to do.

The representation of lists (as singly-linked lists) allows you to
write:

match xs with x :: _ -> x

because that matches on the first cell of the list and binds 'x' to
the head and '_' to the tail. In C the equivalent would be:

struct list {
void *elem; /* bound to 'x' */
struct list *next; /* bound to '_' */
};

Arrays are represented as a flat array of elements in memory (just
like arrays in C). There is no head or tail of an array, only
elements. Thus:

match as with [| x; y |] -> ...

matches a two element array and binds 'x' to the first element and 'y'
to the second element. There is no constructor pattern-matching form
as with lists because there is no constructor / cons cell involved in
the representation.

Rich.

--
Richard Jones
Red Hat

•  1
  New Members