Re: [Caml-list] Lexicographic sort

[Laurent Vibert <lvibert@irisa.fr>]

On Thu, 30 Jan 2003, Francois Pottier wrote:

> 
> Hi,
> 
> I just found a nice way of writing lexicographic sort in O'Caml
> using Luc Maranget's recent extension of pattern syntax, which
> allows a single identifier to be bound in several alternatives.
> 
> For instance, here is code that sorts integer triples:
> 
>   let compare (major1, middle1, minor1) (major2, middle2, minor2) =
>     match major1 - major2, middle1 - middle2, minor1 - minor2 with
>     | 0, 0, d
>     | 0, d, _
>     | d, _, _ ->
> 	d
> 
> Quite beautiful. Perhaps this is obvious to many, but I thought
> I'd post it.
> 

Warning, from the Caml manual,
http://pauillac.inria.fr/ocaml/htmlman/manual014.html
``Or'' patterns :
If both matchings succeed, it is undefined which set of bindings is 
selected

eg. if (0,0,d) and (d,_,_) succeed, you don't hnow the result...
yes in this case, it works, but in some other, it doesn't :
let f = function (_::l) | l -> l
in f [1;2] 

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