Re: if expression and match expression

Zitat von "Oliver Bandel [email protected] [ocaml_beginners]"  
<[email protected]> (Fri, 09 Oct 2015 16:29:22 +0200)

> 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.

typo: I meant: - just reuse the "t" from the match.

(I also prefer "hd" and "tl" over "h" and "t" ...)

Ciao,
    Oliver