Re: if expression and match expression

First of all,
There was a typo in my very initial question.
my has_element1 should be

let rec has_element1 l e =
match l with
| [] -> false
| h::t -> if e = h then true else has_element1 t e;;

Anyway,, Seems everyone got my point. :-) First time to post this
group and very new to ocaml.

I did with ( ) for my second match.

utop[91]> let rec has_element2 l e =
match l with
| [] -> false
| h::t -> ( match h with
            | e -> true
	    | _ -> has_element2 t e
          )
;;


val has_element2 : 'a list -> 'b -> bool = <fun>
Characters 107-108:
Warning 11: this match case is unused.
utop[92]> has_element2 [2;3;4] 10;;
- : bool = true
utop[93]>

Still getting the same warning message with the same result. 


On 10/08 11:19 PM, Hendrik Boom [email protected] [ocaml_beginners] wrote:
> On Thu, Oct 08, 2015 at 08:12:48PM -0700, [email protected] [ocaml_beginners] wrote:
> > Code first:
> >  
> > 
> >  let rec has_element1 l e =
> > match l with
> > | [] -> false
> > | h::t -> if e = h then true else false
> > ;;
> > 
> > let rec has_element2 l e =
> > match l with
> > | [] -> false
> > | h::t -> match h with
> >           | e -> true
> >       | _ -> has_element2 (List.tl l) e
> > ;;
> > 
> >  
> > 
> >  has_element1 works as I expected. 
> > 
> >  And I rewrite has_element1 with replacing 'if expressing' with 'match. 
> > 
> >  But has_element2 always return 'true' and it gives me warning: 'Warning 11: this match case is unused'
> >  
> > 
> >  Questions: 
> > 
> >   (1) Why does my has_element2 always return true? Match expression I 
> > used in has_element2 not the same as if expression in has_element1?
> 
> How is the poor compiler to know whether the last alternative belongs 
> with the first or the second match?  Try inserting ( before the second 
> match keyword and putting its ")" where it belongs.
> 
> I think this may be a language design problem.  But the problem ends up 
> being caught in the type analysis, so it's probably only confusing.
> 
> When OCaml misbehaves I usually find it enlightening to be explicit 
> about types and parentheses.
> 
> -- hendrik

Seungjin Kim