[erlang-questions] List comprehension puzzler

Lloyd R. Prentice <>
Thu Sep 22 03:33:41 CEST 2016


Hi Richard,

I finally had a chance to look closely at the ISBN validator function you sent me. It looks terrific, definitely addresses issues I would not have considered.

So many thanks for taking the time to point the way.

And thanks to all others who posted insights and suggestions.

All the best,

Lloyd

Sent from my iPad

> On Sep 21, 2016, at 9:07 PM, Richard A. O'Keefe <> wrote:
> 
> 
> 
>> On 21/09/16 11:23 PM,  wrote:
>> I'd like to point out that it's straightforward to write
>> >     ...
>> 
>> It's not much harder to write
>> 
>> length_between([_|Xs], L, U) when L > 0 ->
>>    length_between(Xs, L-1, U-1);
>> length_between([], L, U) ->
>>    L =< 0, 0 =< U;
>> length_between(_, _, _) ->
>>    false.
> 
> The third clause was *meant* to be
> 
>  length_between([], L, U)
>    when L =< 0, 0 =< U -> true;
> 
> Free code.  Worth every mill.
> Thanks to Fred Hébert for noticing this.
> Too much coffee, too late at night, and too much
> frustration with AirPort losing the signal every
> few seconds.
> 
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