[REBOL] TECHNICAL ESSAY/CHALLENGE(s) - "Expression Based"? Re:(3)
From: joel:neely:fedex at: 3-Oct-2000 8:04
Another fine response!
[Al--Bri--xtra--co--nz] wrote:
> This is a bit shorter, but still not as nice as the Rebol way as
> used in System and View.
> [
> Rebol [
> File: %Tally.r
> ]
>
> tally: make object! [
> tot: 0
> zero: does [tot: 0]
> up: func [/by n [number!]] [print "up!" tot: tot + either by [n] [1]]
> down: func [/by n [number!]] [print "down!" tot: tot - either by [n]
> [1]]
> now?: does [tot]
> ]
>
> bunchanums: [3 1 35 8 4 5 52 42 19 13 32 43 81 2 6 34 46]
>
> ; A better name for this function would be appreciated.
> mpc: func [Block [block!]] [
> make path! compose Block
> ]
>
Not very inspired, but I'd suggest compose-path as the best I
can come up with.
> ; A better name for this function would be appreciated.
> dr: func [Block [block!]] [
> do reduce Block
> ]
>
Well, inspired by repend I might suggest do-re-me but then I'd
have the entire von Trapp family (and Julie Andrews) accusing me of
theft of "intellectual property"! ;-)
Seriously, we could take inspiration from LISP and call this
function apply as it allows one to apply a (dynamically
determined) function to a (dynamically determined) argument list.
Or perhaps eval would fit???
> use [diffs] [
> diffs: make tally []
> evens: make tally []
> odds: make tally []
> foreach num bunchanums [
> dr [mpc [diffs (either even? num ['up] ['down]) by] num]
> dr [mpc [(either even? num ['evens] ['odds]) up by] num]
> ]
> print ["diffs/now?" diffs/now?]
> print ["evens/now?" evens/now?]
> print ["odds/now?" odds/now?]
> ]
>
> ]
> >> do %Tally.r
[...tracing output snipped...]
> diffs/now? 26
> evens/now? 226
> odds/now? 200
>
All told, I think the two functions above are quite nice! They
certainly handle the diffs case well. I'm a little less cheerful
about how they handle the evens/odds case however, in that they
require that I have a NAME for an object, in order to construct
a path to the needed object/method.
Gabriele's do-in allows me to get at a method of an object with
only the object itself (and the name of the method) in hand, not
requiring a name for the object. This becomes more of an issue
if we generalize my dinky example to other ways we might have
worked with a collection of tally instances. Given Gabriele's
do-in and my tally and data:
>> do-in: func [obj [object!] code [block!]] [do bind/copy code in
obj 'self]
>> tally: make object! [
[ tot: 0
[ zero: does [tot: 0]
[ up: func [/by n [number!]] [tot: tot + either by [n] [1]]
[ down: func [/by n [number!]] [tot: tot - either by [n] [1]]
[ now?: does [tot]
[ ]
>> bunchanums: [3 1 35 8 4 5 52 42 19 13 32 43 81 2 6 34 46]
== [3 1 35 8 4 5 52 42 19 13 32 43 81 2 6 34 46]
...we can say...
>> use [tallies] [
[ tallies: copy []
[ loop 3 [append tallies make tally []]
[ foreach num bunchanums [
[ do-in pick tallies (num // 3 + 1) [up/by num]
[ ]
[ foreach tally tallies [print tally/now?]
[ ]
132
212
82
...without needing to name the members of tallies.
At any rate, between you and Gabriele, we now have nicer solutions
to BOTH variations of my question!
Thanks!
> AllenK has a better grasp of the ideal Rebol way to do this. But
> he says it is difficult to explain. More about this later, or you
> could pester Allen.
> :-)
>
Hey, Allen! Are you there?
Please chime in before Andrew makes me pester you! ;-)
-jn-
