[REBOL] Re: Linguistic influences
From: joel:neely:fedex at: 12-May-2002 6:46
Hi, Ladislav,
Ladislav Mecir wrote:
> 1) I didn't want to criticize the ineffectivity of the algorithm.
> I would rather say, that what matters to me may be a "naturality"
> of the algorithm.
>
FWIW, the algorithm wasn't the point of my note. I really wish I
had chosen a different example. The real point I wanted to focus
on was the contrast between deeply nested expressions vs. a long
sequence of word-setting expressions to build up the result in an
incremental fashion, and the differences in "mental bookkeeping"
required to read and understand each.
> 3) Volker is right, that the introduction of iteration using
> FOREACH simplifies the code. For the comparison purposes, here
> is an iterative version of FLAT-APPEND:
>
> flat-append: func [
> series [series! port!]
> value [any-type!]
> ] [
> either block? get/any 'value [
> foreach element value [
> flat-append :series get/any 'element
> ]
> ] [
> insert/only tail :series get/any 'value
> ]
> :series
> ]
>
Actually, that's still recursive! You refactored the "horizontal"
recursion into the FOREACH, but left the "vertical" recursion in
place. Here's a completely iterative version of the flattener:
nb-flatten: func [
b [block!]
/local front result
][
result: copy []
while [not empty? b][
either block? front: first b [
b: compose [(front) (next b)]
][
insert tail result front
b: next b
]
]
result
]
> 4) I noticed a paradox: the most effective way of assembling blocks
> is to use APPEND (or INSERT TAIL), but we do not have it as a native.
>
Good observation!
-jn-
--
; Joel Neely joeldotneelyatfedexdotcom
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