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Re: request for a new function, say, `sequence'

From: Satyaki Das
Subject: Re: request for a new function, say, `sequence'
Date: Tue, 25 Mar 2003 17:44:02 -0800

Kenichi Handa <address@hidden> writes:

> In your example code, you united the implementaion of range
> and usage of the returned list.  In such a way, of course,
> it is natural that we can make a function that uses `range'
> more concise and efficient.

This should be done only if it doesn't affect the readability and
simplicity of the code.

> > Do you have a counter-example to this?
> How about the code something like this.
> (defvar dev-consonants
>   (append (range (decode-char 'ucs #x0915) (decode-char 'ucs #x0939))
>         (range (decode-char 'ucs #x0958) (decode-char 'ucs #x095F))))
> (defun dev-looking-at-syllable ()
>   (and (memq (following-char) dev-consonants)
>        (looking-at dev-syllable-pattern)))
> The first `memq' is to avoid the heavy `looking-at' in an
> unnecessary case.

This seems like a reasonable usage scenario for `range'. However
since you are doing this for efficiency reasons, isn't it more
efficient to compare with <= than to use memq to to compare it
with 45 separate integers?

> The defvar part can be written as:
> (defvar dev-consonants
>   (append (loop for x from (decode-char 'ucs #x0915) to (decode-char 'ucs 
> #x0939)
>               collect x)
>         (loop for x from (decode-char 'ucs #x0958) to (decode-char 'ucs 
> #x095F)
>               collect x)))

Or you could do it in one loop and collect with a when. But I
agree that this could easily get quite hairy if there are lots of
ranges to consider.

> but using `range' is much more handy and easier to read.


> > IMO, a new builtin function is needed if and only if it makes
> > writing code easier or makes it simpler.
> I'm not requesting a builtin function.

Sorry about the bad terminology. I meant a library function.

>                                         And, `range' surely
> makes writing code easier and makes the code simpler as well
> as dolist, dotimes, while, and etc. do.

Agreed. But I would be careful in its use, since it can
potentially cons a lot (if used inside of a loop for instance).

> > So I suggest that a more descriptive name be chosen -- for
> > instance something like `make-sequence-of-numbers'.
> I don't insist on having TYPE argument, always returning a
> list is ok.  So, for instance, make-number-list, is also
> acceptable.

Yes, this seems reasonable if you don't want the vectors and
string types.


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