Re: [Chicken-users] hash-tables

[Felix Winkelmann]

Am Mon, 24 Nov 2003 11:04:31 +0100 hat address@hidden 
<address@hidden> geschrieben:

> From      : "Felix Winkelmann" address@hidden
> > For short data-sets an association-list will likely be more efficient.
> > Since Chicken uses a copying garbage-collector, one cannot 
> > (unfortunately)
> > just take the address of an object in the heap and use that as a 
> > hash-code
> > (which would be damn fast), so the hash-code has to be computed from
> > the contents of the data. Actually, I exclusively use a-lists, unless
> > I know it's going to be a big table. Doing some benchmarking for your
> > particular application might be worthwhile.
>
> I guess there are time routines for benchmarking purpose, but in the 
> manual I
> find time routines more related to the calendar. What should I use for 
> benchmarks?

[syntax] (time EXP1 ...)
  Evaluates EXP1 ... and print elapsed time and memory information. The 
result of the last expression is returned.

> > > 2) I see in the manual that "get" and "put!" can have a "property"
> > > argument; what's that?
> > >
> >
> > The property may be anything, but it will be compared using `eq?'.
>
> So ??  I do not get the purpose of properties from this reply.

You can put multiple properties under a specific hash-table key.
This is just a thin wrapper around hash-tables that contain
a-lists as values. This is somewhat similar to the "disembodied"
property lists of Common LISP.

(define t (make-hash-table))

(put! t 'michele 'country 'it)
(put! t 'michele 'name 'simionato)

(get t 'michele 'country)   ==>   it


cheers,
felix