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.
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]
]
Why bother?
1) It reduces tedious code.
2) It makes it clear that you're collecting values.
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)
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) tail
dest]
marker: to set-word! word
at-marker?: does [mark/1 = 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) >= 3 [break]]]
collect zz [repeat i 10 [zz: i if i >= 3 [break]]]
collect zz [repeat i 10 [either i <= 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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