# Executing boolean expressions on a list

Peter H|gfeldt <>
Fri Mar 14 03:29:49 CET 2003

```How about lists:all/2,

recursive(N, Es) ->
lists:all(fun(E) -> somef(N, E) end, Es)  ?

/Peter

On Thu, 13 Mar 2003, Shawn Pearce wrote:

> I find I'm writing a lot of:
>
> 	recursive(N, [H | T]) ->
> 		case somef(N, H) of
> 			true ->	recursive(N, T);
> 			false -> false
> 		end;
> 	recursive(N, []) ->
> 		true.
>
> 	somef(N, E) ->
> 		.... % return true or false.
>
> Is there a faster way to write recursive/2 ?  In some cases I have to hand
> around 2 or 3 args instead of just N, but usually they are just payload
> data to somef/2 (or whatever arity) to help it perform its test.  I'm
> just wondering if perhaps there's a faster way to express the case .. end
> in recursive/2.
>
> I'm trying to keep it tail-recursive.  I thought about:
>
> 	recursive(N, [H | T]) ->
> 		if
> 			somef(N, H) -> recursive(N, T);
> 			false -> false
> 		end;
> 	recursive(N, []) -> true.
>
> which I didn't like because of the formatting of the if statement, and:
>
> 	recursive(N, [H | T]) -> somef(N, H) and recursive(N, T);
> 	recursive(N, []) -> true.
>
> but was worried about order of evaluation on the and operator
> and not being able tail-recursive.
>
>
> Feedback from the Erlang pros is good.  ;-)
>
> --
> Shawn.
>
>   Q:	Minnesotans ask, "Why aren't there more pharmacists from Alabama?"
>   A:	Easy.  It's because they can't figure out how to get the little
>   	bottles into the typewriter.
>

```

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