Re: if expression and match expression

Zitat von "Jeremy Yallop [email protected] [ocaml_beginners]"  
<[email protected]> (Fri, 9 Oct 2015 15:13:35 +0100)

> On 9 October 2015 at 14:56, Hendrik Boom [email protected]
> [ocaml_beginners] <[email protected]> wrote:
>> So you'd recommend something like
>>
>> let rec has_element2 l e =
>> match l with
>> | [] -> false
>> | h::t -> h = e or has_element2 (List.tl l) e
>> ;;
>
> List.tl should usually be avoided, too, since it fails on empty lists.
> It's better to use the variable that's bound to the tail of the list
> by pattern matching.

It's at leastmore elegant.
But in the code above, if   "List.tl l" would fail,
then l would be empty, and that means, that the first pattern would
match; and the List.tl would not be called.

But calling  List.tl here would mean doubled extraction of the value,
and therefore be unnecessary computation: the "h::t" already deperated
into head and tail, and then List.tl is called *again*, which means
this could have been avoided - just reuse the "tl" from the match.

Ciao,
    Oliver