Re: [q-lang-users] Special values or failing functions

[Alexander N. <AN...@sp...>]

Hello Albert,

Friday, May 18, 2007, 12:52:10 AM, you wrote:

AG> Alexander Nickolsky wrote:
>> len []    = 0;
>> len [[H|Hs]|T] = _FAIL_;
>> len [H|T]      = 1+len T;
>> 
>> so semantics of _FAIL_ would be : rewrite the current match with
>> itself and return.
>> So, 'fail' applies to the left side, but _FAIL_ applies to the right side.

AG> I don't grok this last sentence. Should 'len [[1,2],3]' return 'len
AG> [[1,2],3]' itself, or _FAIL_, or what? And what should 'len [1,[2,3]]'
AG> return?

I mean 'fail' acts as if the current rule's left side did not match.
_FAIL_ is a regular function. I think 'len [[1,2],3]' should
return 'len [[1,2],3]'. As it has been already mentioned, () is
a great no-value designator.


-- 
Best regards,
 Alexander                            mailto:AN...@sp...