On Mar 27, Ryan Culpepper wrote:
> Eli Barzilay wrote:
> > Here's a suggestion for a small addition to `scheme/base', with the
> > obvious meaning:
> >
> > (with-hash <hash> <key> <expr>)
> >
> > Lookup <key> in <hash> and return the found value. If there is
> > no value evaluate <expr>, store it in <hash> for the <key>, and
> > return it.
> > [...]
> >
> > Any objections?
>
> I don't like the name.
That's the best I could think of -- and the good point in it is that
it's a strong hint that it's a macro.
> I think you should make it a procedure (use the normal hash
> value/thunk convention) and name it 'hash-ref/default!' or something
> similarly descriptive.
That's actually a point that I forgot to mention. At some point,
Matthew made `hash-ref' accept a plain value for a default rather than
a thunk. The reason is that
(or (hash-ref t k #f) ...stuff..)
is faster than putting stuff in a thunk. This is especially important
with hash tables, when you're trying to speed things up.
> Also, how about making it generic instead and adding it to
> scheme/dict? I'd rather procedures for common usage patterns of
> dictionaries were put in scheme/dict than added to the base
> language.
That would of course be useful as a dict method too -- but there's no
contradiction in having both. (As with other methods that correspond
to specific functions -- you pay for the dispatch when you prefer a
generic code.)
On Mar 27, Henk Boom wrote:
>
> If the last argument were a thunk then it would almost make sense to
> just call it 'hash-ref!'. That feels like an oxymoron though =).
That *was* my first choice -- but I didn't want that name for a macro.
--
((lambda (x) (x x)) (lambda (x) (x x))) Eli Barzilay:
http://www.barzilay.org/ Maze is Life!
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