[REBOL] Re: Hashes in Rebol
From: knizhnik:garret:ru at: 9-Dec-2003 22:03
Hello Gregg,
Thank you very much for explanation.
Certainly it is very universal approach to treat everything as
series. But as all universal solutions is is not always convenient to
use:). If I remove exactly one element from the hash - what will be
result of such operation...
But actually I need hash table with integer key (object OID).
And here once again Rebol rules are not compatible with my
expectations:
== make hash! [1 "one" 2 "two"]
>> h select 1
** Script Error: select expected series argument of type: series port
Is it possible to have hash table with integer key?
Or I should first convert it to string?
Tuesday, December 9, 2003, 6:01:44 PM, you wrote:
GI> Hi Konstantin,
KK>> Why them are implemented in Rebol in such strange way?
GI> I think for consistency with other series types. REBOL's standard path
GI> notation is extremely convenient.
KK>> ...how can I
KK>> 1. Remove <key, value> pair from hash
KK>> 2. Change value associated with the particular key
>>> hash: make hash! []
GI> == make hash! []
>>> append hash [A 1 B 2 C 3 D 4]
GI> == make hash! [A 1 B 2 C 3 D 4]
>>> hash/b
GI> == 2
>>> hash/b: 22
GI> == make hash! [A 1 B 22 C 3 D 4]
>>> remove/part find hash 'b 2
GI> == make hash! [C 3 D 4]
>>> hash
GI> == make hash! [A 1 C 3 D 4]
GI> You can also use intermediate words as variables, along with the
GI> get-word! syntax in the path to evaluate them
>>> key: 'c
GI> == c
>>> hash/:key
GI> == 3
GI> But you can't set values that way.
>>> hash/:key: 33
GI> ** Syntax Error: Invalid word -- :key:
GI> ** Near: (line 1) hash/:key: 33
GI> You need to do something like the following:
>>> head change next find hash key 33
GI> == make hash! [A 1 C 33 D 4]
GI> Or write a little wrapper for that (no error handling in example!):
>>> my-replace: func [series key value][change next find series key value]
>>> head my-replace hash 'd 44
GI> == make hash! [A 1 C 33 D 44]
GI> Of course, you could make things work how you want, any number of
GI> ways. e.g.
GI> ; Keys don't *have* to be strings.
GI> ; If you assign a block to _data, it's up to you to make it a hash! if you want.
GI> dictionary: make object! [
GI> ; Odd items are keys, even items are values. I.e.
GI> ; [key1 value1 key2 value2...]
GI> _data: make hash! []
GI> clear: does [_data: make hash! []]
GI> count: does [(system/words/length? _data) / 2]
GI> length?: :count
GI> empty?: does [count = 0]
GI> keys: does [extract head _data 2]
GI> values: does [extract next head _data 2]
GI> item: func [key] [
GI> if has-key? key [_data/:key]
GI> ]
GI> has-key?: func [key] [
GI> found? find/skip _data key 2
GI> ]
GI> remove: func [key] [
GI> if has-key? key [system/words/remove/part find/skip _data key 2 2]
GI> ]
GI> change: func [key value] [
GI> either has-key? key [_data/:key :value][append _data reduce [key :value]]
GI> ]
GI> contains?: func [value /only] [
GI> either only [
GI> found? find/skip/only next _data value 2
GI> ][
GI> found? find/skip next _data value 2
GI> ]
GI> ]
GI> ]
GI> ;d: make dictionary []
GI> ;d/_data: ["A" 1 "B" 2 "C" 3 "D" 4]
GI> ;d/change 0.0.0 "black"
GI> ;d/item 0.0.0
GI> In your case that might be a good choice, but the main thing to look
GI> at for "normal" REBOL usage is how the model fits with standard REBOL
GI> idioms and style. REBOL is quite different from other languages, and
GI> sometimes trying to make it work like them will look good initially,
GI> because you're making it act in a familiar way. Sometimes, though, it
GI> will lead to inelegant solutions later because you just keep adding
GI> things, rather than stripping them away.
GI> The main thing to remember with REBOL is that everything is just
GI> data--a series of values--until it is evaluated.
GI> HTH!
GI> -- Gregg
--
Best regards,
Konstantin mailto:[knizhnik--garret--ru]
