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

[Shiro K. <sh...@la...>]

From: Jens Thiele <ka...@be...>
Subject: Re: [Gauche-devel] seq-null?, seq-empty?, collection-null? or collection-empty?
Date: Fri, 25 Jun 2010 19:36:01 +0200

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

> Regarding collections-empty? I am not sure about the use cases, though i
> remember at least once looking for hash-table-empty? Unfortunately I
> can't remember in what context.
> 
> jens
> 
> PS: just as side-note: i also would prefer -empty? over -null? and I
> think it is a bit unfortunate that there is such a mix:
> 
> from the info index:
> 9 matches for "null\?\|empty\?" in buffer: *info*
>     205:* attlist-null?:                         SSAX data types.     (line 142)
>    1223:* hook-empty?:                           Hooks.               (line  39)
>    1934:* null?:                                 List predicates.     (line  10)
>    2149:* queue-empty?:                          Queue.               (line  25)
>    2205:* rbtree-empty?:                         Red black tree.      (line  42)
>    2929:* stream-null?:                          Stream library.      (line  22)
>    3060:* string-null?:                          SRFI-13 String predicates.
>    3632:* tree-map-empty?:                       Treemaps.            (line  31)
>    3977:* vector-empty?:                         Vector library.      (line  34)

Yeah I do prefer 'empty?', too.  The 'null?' came from existing
standard and/or library.

--shiro