[racket] Little Schemer, lat?

2015-01-02 23:58 GMT+01:00 Frank Weytjens <fweytjens.android at gmail.com>:
> Happy new year Racketeers,

> An empty list is a list, but is it a lat ?

> If you give an empty list as argument to the lat?-function, the answer is
> yes. But an atom must be a string of characters or numbers, or even one
> character, or a combination of special characters as long as it is not an (
> or an ). The empty list contains no characters at all, so it can not be a
> list of atoms.

> Then an empty list can be anything.

To some degree it is a matter of convention. This illustrates the
usual convention:

Is this is a list of (person) names?
     Alice, Bob, Charlie
Yes, all items on the list are names.

Is this a list of names?
     Alice, Bob, Cat
No, since Cat is not a name.

Is this (the empty list) a list of names?
     <nothing>
Yes, there are no non-names on the list.
In other words all items on the list are names, which makes it a list of names.

The empty list is also a list of cheeses.


--
Jens Axel Søgaard