The body of the explicit verb is considered to be a list of lines, i. e.
a rank-2 array of characters.
Henry Rich
On 7/27/2019 7:50 PM, Linda Alvord wrote:
It seems not to matter that 1 is in parentheses:
g=:13 :'1 x}y'
1 3 5 g i.10
0 1 2 1 4 1 6 7 8 9
g
4 : '1 x}y'
But hee is a surprise.
Itemize (,:y) shows up.
5!:4 <'g'
┌─ 4
── : ─┴─ ,:'1 x}y'
$'1 x}y'
5
$,:'1 x}y'
1 5
Why is this here?
Linda
-----Original Message-----
From: Programming <[email protected]> On Behalf Of Roger
Hui
Sent: Saturday, July 27, 2019 1:06 AM
To: [email protected]
Subject: Re: [Jprogramming] Learning Tacit Programming
13 : '(1) x}y' or 13 : '1 x}y' can not be made tacit because they use a function
argument (x) as an operand. Similarly 13 : '+/"y x' or 13 : '+/"x y' can not
be made tacit either.
Why not, you might ask? The sequence for an operator is that you _first_ derive a
function, and _then_ the function is applied to function arguments x and/or y . When you
say x} or +/"x or +/"y , at that point you don't yet have the function
argument.
On Fri, Jul 26, 2019 at 9:40 PM Devon McCormick <[email protected]> wrote:
I am intrigued by tacit programming but agree with Henry that you
should drink the Kool-Aid with slow, measured sips.
I continue to rely heavily on "13 : .." (to the dismay of tacit
die-hards) but still puzzle over why certain expressions cause it to give up,
e.g.
13 : '(1) x}y'
4 : '(1) x}y'
Yet this works
x=. 2 4 6
y=. i.10
(1) x}y
0 1 1 3 1 5 1 7 8 9
Whereas these do not:
x ((1) [}]) y
0 1 2 3 4 5 6 7 8 9
x ((1)& [}]) y
0 6 2 3 4 5 6 7 8 9
On Fri, Jul 26, 2019 at 11:53 PM Henry Rich <[email protected]> wrote:
Yes, you have to think differently.
Please, don't make a fetish of tacit programming. The important
thing about becoming a J programmer is training yourself to look at
the whole problem rather than working with atoms. That is, getting
over the loop mindset.
Problem: You have an array a and you want to apply a linear function
y=3x+1 to every atom. How do you do it?
0. (3 * a) + 1
Bravo! You didn't have to loop. Full marks.
1. 1 + 3 * a
Piu bravo! You are thinking right to left.
2. (1 + 3&*) a
Bravissimo! You have written a little bit of tacit code. You could
also have written (1 + 3 * ]) a
3. 1 3 p. a
Congratulations, you have reached master level. Let the interpreter
sweat the details.
My very first J program was a model of texture processing for a
computer-graphics system. I imbibed the tacit liquor too deeply,
and wrote the whole thing as a sequence of tacit verbs, 50 of them.
It worked. It was absolutely unmaintainable. Don't go there.
Use tacit verbs for problems whose spec is mathematically unchangeable.
For everything else, use explicit verbs.
Henry Rich
On 7/26/2019 7:20 PM, The3DSquare Josh Yang wrote:
I was wondering if you guys have any resources for learning tacit
programming in J. I've been struggling with tacit programming,
probably because all the other programming languages are mainly explicit.
Something
like "Tacit programming for the explicit programmer" would be
great
since I
often fail to derive the tacit equivalent of a series of explicit
eeaxpressions (especially when there are mutable variables).
I know I need to think differently, but having some guidance would
help greatly.
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