Re: [Chicken-users] Question regarding "length"

[Kon Lovett]

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On May 29, 2006, at 2:38 PM, Alejandro Forero Cuervo wrote:

> > What is the list length of (1 . 2) anyway? Only 1 makes sense.
>
> Hmm, I think throwing an error, ―just like (length 'foo) does―, would
> make more sense than returning 1 for (length '(1 . 2)).

Yes, if length were re-defined to accept improper & circular lists.  
But, since 1) length is less than 1% of core procedure calls in my  
corpus of scheme code (~5000 files), 2) generally used after  
determination of list kind, 3) procedure contracts generally state  
with which kind of list they will work, and 4) scheme procedures are  
not required to be bullet-proof - caveat emptor, I don't feel compelled.

SRFI-1 states for an implementation "It is an error to pass a value  
to length which is not a proper  list (finite and nil-terminated)"  
and "In particular, this means an  implementation may diverge or  
signal an error when length is  applied to a circular list." It  
doesn't say "must signal an error" for an improper list nor "must  
signal an error for a circular list." Chicken meets these conditions.

If coding to the "standard" one must take the above into account  
anyway. Having chicken 'length' barf won't change that.

> Same goes for a circular list: throwing an error would make more sense
> than failing to return, the small overhead required to detect circular
> lists considered.
>
> Alejo.
> http://azul.freaks-unidos.net/

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