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AW: AW: AW: Several comments

This page is part of the web mail archives of SRFI 43 from before July 7th, 2015. The new archives for SRFI 43 contain all messages, not just those from before July 7th, 2015.

> They are like the empty set: they seem odd only until they seem second
> nature, at which point they are ordinary and boring.  Rather like
> zero, actually.
> What is slightly odder is a matrix of dimension zero; such a matrix
> necessarily has no elements.  This is unusual, because for any other
> dimension, a single-element matrix is possible.  That means that you
> can convert scalars to matrixes for any dimension but zero.
> Still, not a big deal.

All right then, from a mathematical point of view, zero-dimensional vectors
are nothing special.

But what about the usage of vectors as a type of data structure? In general,
vectors are allocated with a fixed length, in order to allow access to the
individual elements of the vector in constant time. In some programming
languages, the length of a vector is immutable, once defined, while other
programming languages allow vectors to be resized (R5RS does not). Still, I
would claim that vectors are not dynamical data structures that routinely
have length zero.

On the other hand, I have to admit that several functions defined by SRFI-43
will return zero-dimensional vectors on occasion.

Probably, I'm just too conservative. Anyway, I retract any objections
against defining the predicates vector-empty? and vector-nonempty?.


Michael Burschik