On 5/10/06, Gregg Irwin <[EMAIL PROTECTED]> wrote:
>
> Hi All!
>
> I've posted this before--never got much response--but I'll try again,
> since I really want to pester Carl to add something like this to R3 if
> others think it would be useful.
>
> What is it?
>
> A function to collect values into a block, so you can avoid the
> local/copy/append/return dance in functions. e.g.
>
> fn: func [series /local res] [
> res: copy []
> foreach val series [append res val]
> res
> ]
>
> It was inspired by Brett Handley and Romano Paolo Tenca. I just
> came up with a different approach that worked better for me.
>
I like that topic. Hard to find the one true universal solution. :)
> How does it work?
>
> It takes a word and a block as arguments. Anytime the word appears
> as a set-word! in the block, the value assigned to it is
> "collected".
>
> The above func would look like this:
>
> fn: func [series] [
> collect v [foreach val series [v: val]
> ]
>
Looks good.
> Why bother?
>
> 1) It reduces tedious code.
>
> 2) It makes it clear that you're collecting values.
>
[rebol []
{
Once i used this, its inspired by Carl convention to use 'emit,
and is short:
}
collect: func [out code /local emit] [
emit: func [val] [
repend out val
]
do bind code 'local
]
probe collect copy [] [
foreach val [1 2 3 4] [
emit val * 2
]
]
{
Now i prefer something like this
(interface debatable, quick patch of forskip. How about [val series body] ?=
):
}
change-each: func [
[throw catch] 'word [word!] body [block!] /local orig result
] [
if not any [
series? get word
port? get word
] [throw make error! {change-each expected word argument to
refer to a series or port
!}]
orig: get word
while [not tail? get word] [
change/only get word do body
set word next get word
]
set word orig
]
data: copy [1 2 3 4]
probe change-each data [
data/1 * 2
]
?? data
{
But adds only one value per loop, while the other version , like yours, all=
ows
collect[emit [<html><body>] foreach val data[emit val] emit [</body></html=
>]]
}
wait 4 quit
]
> What are the downsides?
>
> It's a subtle dialect that overrides the meaning of set-words.
> (I've been using it for quite a while now, so I can't judge how
> unnatural it feels to others)
>
Thats one reason to use 'emit instead of set-words.
> Where's the code?
>
> collect: func [
> [throw]
> {Collects block evaluations.}
> 'word "Word to collect (as a set-word! in the block)"
> block [any-block!] "Block to evaluate"
> /into dest [series!] "Where to append results"
> /only "Insert series results as series"
> /local code marker at-marker? marker* mark replace-marker rules
> ] [
> block: copy/deep block
> dest: any [dest make block! []]
> ; "not only" forces the result to logic!, for use with PICK.
> ; insert+tail pays off here over append.
> ; FIRST BACK allows pass-thru assignment of value.
> code: compose [first back (pick [insert insert/only] not only) ta=
il dest]
> marker: to set-word! word
> at-marker?: does [mark/1 =3D marker]
> ; We have to use change/part since we want to replace only one
> ; item (the marker), but our code is more than one item long.
> replace-marker: does [change/part mark code 1]
> marker*: [mark: set-word! (if at-marker? [replace-marker])]
> parse block rules: [any [marker* | into rules | skip]]
> do block
> head :dest
> ]
>
> Got any examples?
>
> collect zz []
> collect zz [repeat i 10 [if (zz: i) >=3D 3 [break]]]
> collect zz [repeat i 10 [zz: i if i >=3D 3 [break]]]
> collect zz [repeat i 10 [either i <=3D 3 [zz: i][break]]]
> dest: copy []
> collect/into zz [repeat n 10 [zz: n * 100]] dest
> collect zz [for i 1 10 2 [zz: i * 10]]
> collect zz [for x 1 10 1 [zz: x]]
> collect zz [foreach [a b] [1 2 3 4] [zz: a + b]]
> collect zz [foreach w [a b c d] [zz: w]]
> collect zz [repeat e [a b c %.txt] [zz: file? e]]
> iota: func [n [integer!]][collect zz [repeat i n [zz: i]]]
> iota 10
> collect zz [foreach x first system [zz: to-set-word x]]
> x: first system
> collect zz [forall x [zz: length? x]]
> x: first system
> collect zz [forskip x 2 [zz: length? x]]
> collect/only zz [foreach [a b] [1 2 3 4] [zz: a zz: b zz: reduce =
[a b a + b]]]
> collect/only zz [
> foreach [a b] [1 2 3 4] [
> zz: a zz: b zz: reduce [a b a + b]
> foreach n reduce [a b a + b] [zz: n * 10]
> ]
> ]
>
> dest: copy ""
> collect/into zz [repeat n 10 [zz: n * 100 zz: " "]] dest
>
> dest: copy []
> collect/into zz [
> foreach [num blk] [1 [a b c] 2 [d e f] 3 [g h i]] [
> zz: num
> collect/only/into yy [
> zz: blk
> foreach word blk [zz: yy: num yy: word]
> yy: blk
> ] dest
> ]
> ] dest
>
> Comments?
>
> This is where you come in.
>
> Is it something worth asking RT to include?
>
> How could it be improved?
>
>
> -- Gregg
>
> --
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>
>
--=20
-Volker
"Any problem in computer science can be solved with another layer of
indirection. But that usually will create another problem." David
Wheeler
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