Hashtables are functions

In the same spirit as vectors, hashtables can be thought of as functions that map keys to values. muSE hashtables are presented exactly like that and don't need special accessor functions.

> (define rgb (mk-hashtable))
> (rgb 'red 255)
> (rgb 'green 255)
> (rgb 'blue 255)

If you load the above definitions, you can get an alist from the hash table using -
> (hashtable->alist rgb)
which will give
((red . 255) (green . 255) (blue . 255))
(The order is unspecified, though.)

You can retrieve the green component using (rgb 'green). If you supply a key that is not present in the hashtable, the function will return (). In muSE therefore, it is not possible to distinguish between a key with a value that is () and a key that is not present in the hashtable. This fact is used to remove a key from the hashtable if you pass () as the value argument. For example -

> (rgb 'green ())
> (hashtable->alist rgb)
((red . 255) (blue . 255))

This is not really a restriction and you can use a hashtable as a set by setting the value to any non-NIL value.

Hashtables accept integers, strings and symbols as keys. Therefore, you can use a hashtable like a sparse vector if need be, since they both have the same invocation interface.