Re: [Caml-list] short-circuit in Real World Ocaml ch 3 deserves a comment

[Nicolas Braud-Santoni <nicolas@braud-santoni.eu>]

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On 19/11/2013 16:05, Jean Saint-Remy wrote:
> The example code using pattern matching appears to be a "let rec"
> short-circuit which I believe deserves a comment in the book. It
> appears to be puzzling, we are binding a "zero" to the head of the
> list in order to drop it? I think it is a fine example of OCaml that
> should be encouraged, not just an isolated case.
>
> let rec drop_zero ls = match ls with
>   | [] -> []
>   | 0 :: tl -> drop_zero tl
>   | hd :: tl -> hd :: drop_zero tl
> ;;

Hi,

It isn't a « short circuit » : the list is pattern matched, and if it
matches `0 :: tl`, then the result is `drop_zero tl`.
The head of the list (0) is effectively dropped by not including it on
the right hand side.

And, as far as I know, it is rather idiomatic to use pattern matching in
the way (when matching over suitable datatypes).


Regards,
Nicolas


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