[pro] "fhash"

[Daniel Weinreb]

Could you tell me where to find that?  Thanks. -- Dan

On Tue, Jun 14, 2011 at 3:50 AM, Alessio Stalla <alessiostalla at gmail.com>wrote:

> On Tue, Jun 14, 2011 at 9:37 AM, Marco Antoniotti
> <antoniotti.marco at disco.unimib.it> wrote:
> >
> > On Jun 13, 2011, at 21:18 , Daniel Weinreb wrote:
> >
> >> Friends,
> >>
> >> I wrote a little package for "fash hash tables", which provide an
> >> abstraction that is analogous to that of Common Lisp hash tables, but
> >> is faster for tables with few elements, and only slightly inferior for
> >> tables with many elements.
> >>
> >> I did this because performance analysis showed that our system was
> >> spending too much time in hash table operations, and using the new
> >> package helped.
> >>
> >> I have recently been cleaning this up, one reason being that I'd like
> >> to open source it.  The function names used to be things like getfhash
> >> and mapfhash.  Now they are like fhash:get and fhash:map-elements and
> >> so on.
> >>
> >> However, before I open-source it, I was to make sure it's "right".  It
> >> recently occurred to me that the package name "fhash" has problems.
> >>
> >> Here are pros and cons of changing it that I can see.
> >>
> >> Pro: I's not a hash table in the small-cardinality case; it's a linear
> >> lookup.  So the name is not actually accurate.
> >>
> >> Pro: Calling such a data structure a "hash table", even as Common Lisp
> >> does, is an abstraction violation.  Whether it works by hashing is an
> >> implementation detail.  The Java collection library calls this a Map.
> >> Python calls it a dictionary.  Clojure calls it a map.  Those are both
> >> better names.
> >
> > Actually, in Java the naming reflects the separation between abstraction
> and implementation.  AFAIU, clojure does not quite do this and neither does
> Python.
> >
> > I would advocate settling down on a Java-esque nomenclature with MAP or
> DICTIONARY as "names" for the abstraction and with different names for the
> implementations; e.g.,  DICTIONARY-TREE, DICTIONARY-FHASH,
> DICTIONARY-HASH-TABLE, you name it....
>
> AFAIK, Java started just like Lisp with the Hashtable class
> (implementation without interface) which later was deprecated in favor
> of Map (interface) + HashMap, TreeMap, ... (implementations).
> There is already a somewhat official API for extensible sequences,
> designed by Christophe Rhodes and implemented in SBCL and ABCL (and
> maybe others, I don't know). We could similarly have extensible maps,
> even though "sequence" is an already recognized abstraction in CL,
> while "map" is not.
>
> Alessio
>
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