Subject: Re: [SWIPL] Type error vs. silent failure

From: Jan Wielemaker <[email-masked]>
Date: Fri, 26 Oct 2001 15:37:29 +0200

On Fri, 26 Oct 2001, Paulo Moura wrote:
>On Sexta, Outubro 26, 2001, at 12:01 , Jan Wielemaker wrote:
>
>> Gernot,
>>
>>> [ Sorry, must have been discussed in the past, but couldn't find 
>>> anything ]
>>
>> Not on this list, but in general, I assume it must be.
>>
>>> Is there any rational behind
>>>    nth1(a, [a,b,c], X).
>>> failing silently and
>>>    length([a,b,c], a).
>>> giving a type error?
>>
>> Not really, apart from the fact that length is part of the ISO standard
>> and the standard prescribes the tests to be made and the exceptions they
>> should raise, while nth1/3 isn't.
>
>Hum? I'm almost certain that length/2 is NOT in the ISO standard.

Oops, you're right.  The argument still holds for things that are
though as well as the remainder of my post is still explaining the
existing difference.

	Sorry --- Jan