Re: [Gauche-devel] seq-null?, seq-empty?, collection-null? or collection-empty?

[Jens T. <ka...@be...>]

Shiro Kawai <sh...@la...> writes:

> From: Jens Thiele <ka...@be...>
>
>> I first was looking for seq-empty? and seq-null? Only, after I didn't
>> find it I thought: "hmm maybe look for collection-empty/null?"
>> 
>> My usage often would be to replace null? with seq-empty/null?, using
>> (ref <> 0) as car replacement and (subseq <> 1) as cdr replacement.
>
> Although symmetry to lists is nice, you usually want to avoid
> that pattern, since subseq may take O(n) time and/or space;
> you'll never know.
>
> I tend to think it would be better to provide a wrapper;
> that is, 
>
>  (first <sequence>) -> element
>  (rest <sequence>) -> <wrapped-sequence>
>
> where <wrapped-sequence> wraps any concrete sequence type.
> For a vector, it can hold the original vector and an index,
> hence it's O(1).  

ups - i somehow thought subseq does that in some way

> Still it would be slower than the implicit
> iterator constructs such as fold and for-each, which are
> recommended over this first/rest idiom.

i see - thanks!
... leaving to grep for subseq ... ;-)